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DRAFT PROPOSAL FOR A NEW GUIDELINE

Mysid Two-Generation Test Guideline

April 2013

INTRODUCTION

1. This guideline describes a two-generation test with an estuarine mysid that considers reproductive 

fitness in parents and offspring as an integrated measure of toxicant exposure. It also enables measurement of a 

suite of other endpoints that allow for diagnostic and definitive evaluation of endocrine disrupting chemicals 

(EDCs) or other types of reproductive toxicants (Verslycke et al 2004). This guideline is intended to be 

applicable to the mysid, Americamysis bahia, but could be adapted to other mysid species. The mysid twogeneration test is a relatively long-term (normally 60-d or longer) assay that assesses early development, 

growth, and reproduction in two generations (F0 and F1). The two-generation test described in this guideline 

is an extension of existing standard practice for conducting a mysid life-cycle test (ASTM 2005; McKenney 

1986, 1998; and Nimmo et al 1977, 1978). 

2. The test is intended to serve as a definitive test with an aquatic arthropod for collecting 

concentration-response information on adverse effects suitable for use in ecological risk assessment. 

Specifically, the design enables the collection of both organismal toxicity data and information concerning 

various aspects of the reproductive biology and life-stage viability. The former is useful as a basis for better 

understanding comparative toxicological relationships across biological groups and/or extrapolation across 

species (McKenney 1986, 1996), while the latter are critical to application of population models to risk 

assessment scenarios (Raimondo and McKenney 2005a,b).

3. The two-generation test is initiated with newly-released <24 hours old (F0 generation) offspring that 

are grown to maturity and then their offspring collected (F1 generation). The F1 generation is also grown to 

maturity and their offspring enumerated (F2 generation). Development, sexual maturation, reproduction, and 

growth are observed in the F0 and F1 generations. Measurements are made of a number of endpoints in both 

F0 and F1 generations reflective of functional endocrine regulation of development, growth, and reproduction, 

including sex ratio, time to maturity, time to brood release, and interbrood duration (which, when combined 

with growth rates, are reflective of the molting process).

PRINCIPLE OF THE TEST

An overview of the methodology and relevant test conditions is provided in Table 1 (Annex 1). 

4. Parental mysid exposure (F0) - For the recommended species (Americamysis bahia), the test protocol 

is initiated with healthy newly released mysids less than 24 hours old. The test is conducted with a minimum 

of five chemical concentrations, as well as appropriate controls, with a minimum of three experimental units 

(replicates) per treatment. In general, each replicate tank contains two retention baskets, each holding 20

mysids per basket (one basket housing animals used for reproduction observations and a second basket for 

growth and optional biochemical measurements). With the appearance of a marsupial pouch on females, 

mature females are isolated as pairs with males (smaller individuals without marsupial pouches) in separate 
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brood cups. The exposure of these F0 mysids is terminated after the second brood release is complete (or 7 

days past the median second brood release in controls). Toxicant and control treatments are delivered to the 

mysids in water which is delivered by a continuous flow apparatus (e.g., infusion pumps) (McKenney 1982) or 

an exposure apparatus using intermittent flow (e.g., proportional diluter) (McKenney 1998). Daily 

observations are assessed and recorded for each individual on mortality, sex determination, reproductive 

condition of female (marsupial pouch with or without developing embryos), and number of young released in 

each of the first two broods. At weekly intervals (Day 7 and Day 14) animals from the growth baskets are 

subsampled for growth measurements (length and dry weight; see section 34 for details).

5. F1 generation – Offspring (F1) from the parental generation (F0) are collected each morning from the 

brood cups and transferred immediately to baskets (labeled with the date), which are housed within separate 

tanks for each of the F0 exposure conditions. Optimally, two groups of 15 F1 juveniles are selected and 

maintained within separate baskets for each of the F0 exposure conditions (one housing animals used for 

reproduction observations and a second basket for growth and optional biochemical measurements). 

Observations are assessed for each individual and recorded daily on mortality, sex determination, reproductive 

condition of female (marsupial pouch with or without developing embryos), and number of young released in 

each of the first two broods. F1 adults may be discarded or saved for subsequent measurements (e.g., if stagespecific survival is measured for population modeling) after release of their second brood. At weekly intervals 

(Day 7 and Day 14) animals from the growth baskets are subsampled for growth measurements (length and dry 

weight).

DATA ENDPOINTS

The test method includes study variables and biological endpoints which are recorded per 

mysid or composite of mysids, per breeding pair, or per replicate tank (i.e. growth or reproduction 

basket). These endpoints were divided among three categories:

(i) Study Parameters (F0, F1)

a. Study day 

b. Exposure duration

c. Pairing day

(ii) Reproduction (F0, F1) (11)

d. Sex ratio (per tank; i.e. both growth and reproduction baskets)

e. Time to maturity (per tank; i.e. both growth and reproduction baskets)

f. Time to first brood release (per breeding pair)

g. Time to second brood release (per breeding pair)

h. Interbrood duration, time between release of first and second brood (per breeding pair)

i. Number of young per female in the first brood (per breeding pair)

j. Number of young per female in the second brood (per breeding pair)

k. Total number of young in the first two broods per female (per breeding pair)

l. Total number of offspring per female (per breeding pair)

m. Percentage of females that are reproductively active in the first two broods (per 

breeding pairs)

n. Total reproduction days in the first two broods (per breeding pairs)
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o. Sex ratio (per replicate tank)

p. Number of young per female per reproductive day in the first two brood (per breeding 

pair)

(iii) Survival (F0, F1) (10)

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a. Survival rate for all animals including both the growth and reproduction animals at days 7, 14 

and termination (per tank)

b. Gender-specific mortality (per breeding pairs)

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The survival rates were adjusted for the non-treatment related deaths and animals removed from growth baskets for 

morphometric measurements. 

(iv) Growth (F0, F1) (8)2

a. Length at day 0 (per mysid)

b. Length at day 7 (per mysid)

c. Length at day 14 (per mysid)

d. Length at termination. (per mysid)

e. Weight at day 0 (per mysid)

f. Weight at day 7 (per mysid)

g. Weight at day 14 (per mysid)

h. Weight at termination (per mysid)

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Day 14 and terminal weights and lengths are reported by gender.

DESCRIPTION OF THE METHOD

Test animals and assay system

Test animals

7. The test should be started with newly released mysids (<24 hours old). The mysid Americamysis 

bahia Molenock, 1969 (formerly Mysidopsis bahia) is the organism specified for these tests. Mysids should 

originate from laboratory cultures in order to ensure the individuals are of similar age, appearance, size, and 

experimental history. All organisms used for a particular test should have originated from the same culture 

population. Mysids used for establishing laboratory cultures may be purchased commercially or collected 

from appropriate natural areas. Because of similarities with other mysid species, taxonomic verification 

should be obtained from the commercial supplier, by experienced laboratory personnel, or conducted by an 

outside expert. Records should be kept regarding the source of the initial stock and culturing techniques.

8. Mysids should not be used for a test:

(a) If more than 10 percent of the stock culture die or show signs of stress during the 14 days 

preceding the test;

(b) If they exhibit abnormal behavior;

(c) If they or the brood stock have been used in a previous test, either in a treatment or in a control 

group.
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9. Care and handling. 

(a) Mysids should be cultured in dilution water under similar environmental conditions to those used 

in the test. Optimal test conditions of 26 ± 1° C and 20 ± 2 o

/oo S are recommended based on 

previously determined optimal salinity-temperature conditions for survival (McKenney 1994), growth 

(McKenney and Celestial 1995), and reproduction (McKenney 1996). The brood stock must be 

maintained in dilution water at the test temperature for at least 14 days prior to the start of the test. 

(b) Organisms should be handled as little as possible. When handling is necessary it should be done as 

gently, carefully, and quickly as possible. When removing retention baskets containing mysids from 

aquaria, rotate the basket gently back and forth and then slowly remove it from the water. 

Immediately examine the mesh on the inside of the basket and gently rinse any stranded mysids off the 

mesh. During culturing and acclimation, mysids should be observed carefully for signs of stress, 

physical damage, and mortality. Dead and abnormal individuals should be discarded. Organisms that 

touch dry surfaces or are dropped or injured during handling should be discarded. 

(c) Fine mesh dip nets are best for removing gravid female mysids from brood stock tanks. Wide bore 

pipettes or smooth glass tubes equipped with rubber bulbs can be used for transferring <24-hour-old 

mysids. Care should be exercised to avoid bubbles in the pipette because they might allow mysids to 

become lodged on the side of the pipette. 

10. Feeding. During the test, the mysids should be fed the same diet as used during culturing and 

acclimation. Any food utilized should support survival, growth, and reproduction of the mysids. A 

recommended food is live Artemia spp. nauplii provided ad libitum. Fish fed nauplii obtained at 24-h-post 

hydration of cysts showed pronounced increases in growth compared to 48-h Artemia (Ablett and Richards 

1980), and accordingly, it is recommended that 24-hour-old nauplii be used to feed both cultured and test 

mysids. Variations in survival, growth, and reproduction of A. bahia have been found in connection with 

different geographic sources and strains of Artemia (Johns et al 1981), and these variations in mysid 

performance have been correlated with differing fatty acid profiles and the availability of essential fatty acids 

in the Artemia nauplii (Léger at al 1985, 1986). For these reasons, use of reference Artemia cysts for which 

fatty-acid content has been determined are recommended for use in the mysid two-generation protocol 

(Sorgeloos 1980; Léger et al 1986). The fatty-acid profile of the brine shrimp may be improved enhanced by 

exposing them to supplements that provide additional highly unsaturated fatty acids (HUFA), especially 

docosahexaenoic acid (DHA), and eicosapentaenoic acid (EpA), both of which are relatively poor in natural 

strains of Artemia (Hanaee et al. 2005). Hanaee et al. (2005) found that enriching Artemia cysts increased the

HUFA content of nauplii about 1.6 times and the DHA and EpA content by 1.2 and 84 times, respectively.

Culturing newly hatched Artemia with nutritional supplements suitable for aquaculture (e.g. SELCO) and to 

reduce pathogen transfer (e.g. SANOCARE) according to manufacturers’ recommendations is recommended. 

Nauplii concentrations shown to maximize reproduction in A. bahia (McKenney 1987) should be used as a 

guideline, and concentrations should be adjusted so that nauplii are continually available in baskets (nauplii 

can be found in the basket the next day). Densities of nauplii (per ml) from Artermia cultures (prepared daily 

from hydrated cysts) should be determined by replicate counts of aliquots pipetted onto filter paper. Based on 

these densities, various volumes of nauplii are fed twice or three times per day to mysids in accordance with 

the following regime: rations for growth baskets and survival/reproduction baskets should be approximately 

3600 nauplii/basket on days 1-3, 4500 on days 4-6, 5400 on days 7-9, 6300 on days 10-12, and 7400 on days 

>12, while brood cups are fed approximately 1800 nauplii/cup throughout the test. Feeding should be adjusted 

appropriately based on flow rates in aquaria, reproductive output, and presence of unconsumed Artemia 30 

minutes after feeding. Adequate feeding can often be determined observationally based on the color change to 

mysids due to the presence of Artemia in the alimentary canal. All treatments and controls should receive, as 

near as reasonably possible, the same ration of food. 
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11. Acclimation. 

(a) Any change in the temperature and chemistry of the water used for holding or culturing the test 

organisms to those of the test water should be gradual. Within a 24-h period, changes in water 

temperature should not exceed 3 o

C, while salinity changes should not exceed 3 ppt. 

(b) During acclimation, mysids should be maintained in facilities with background colors and light 

intensities similar to those of the testing areas.

Water

12. Natural or artificial seawater is acceptable as dilution water if mysids will survive and successfully 

reproduce in it for the duration of the culturing, acclimating, and testing periods without showing signs of 

stress, such as reduced growth or fecundity. Mysids should be cultured and tested in dilution water of the same 

origin. Natural seawater should be filtered through a filter with a pore size of < 20 μm prior to use. Artificial 

seawater can be prepared by adding commercially available formulations or by adding specific amounts of 

reagent-grade chemicals to reagent water (deionized, distilled, or reverse osmosis water).

13. The temperature, salinity, pH, and dissolved oxygen should be measured in the dilution water at the 

beginning of each test. Thereafter, the temperature of the exposure water should be monitored continuously 

and salinity daily, while pH and dissolved oxygen concentrations are to be measured at least weekly in the 

exposure water within each replicate chamber. Measurement of total organic carbon (TOC) in the dilution 

water at the beginning of the test may also be desirable and is necessary for testing with cationic substances. 

The dilution water should have the following characteristics at test initiation: 

(a) Dissolved oxygen should be between 80 and 100 percent saturation. If necessary, the dilution 

water can be aerated before the addition of the test material. 

(b) Salinity should be between 18 and 22 o

/oo S.

(c) The pH should be between 7.6 and 8.2 

(d) With cationic test material the TOC should be less than or equal to 5 mg/L. 

Assay system

14. The design and materials used for the exposure system are optional; basically, any system that enables 

conformance with the performance-based criteria described below related to chemical delivery, water quality, 

and animal health is acceptable. Glass, stainless steel, or other chemically inert material should be used for 

construction of the test system. The dimensions of the test chambers must be such that the animals can interact 

in a fashion conducive with successful reproduction. 

15. Proportional diluters, metering pumps, or other suitable systems should be used to deliver test material 

to the test chambers. The choice of a specific delivery system depends on the specific properties and 

requirements of the test material. The system shall be calibrated before each test. Calibration includes 

determining the flow rate through each chamber and the concentration of the test material in each test chamber

(within 20% of nominal). If actual concentrations differ by greater than 20%, the cause should be identified in 

order to bring the concentrations closer to nominal.
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16. A closed flow-through system may be used to test volatile compounds when more than 20 percent of 

the test material would be lost through volatility. A description of the design of this type of system should be 

included in the study report.

17. Mixing chambers containing test material should not be aerated.

18. Test chambers should be constructed of chemically inert material and be of suitable capacity. Mysid 

juveniles should be held in retention baskets constructed of 15-cm glass Petri dish bottoms to which a 15 cm 

high cylinder of nylon mesh screen (250-350 μm mesh) has been attached with aquarium grade (without 

fungicides) silicone adhesive, within test chambers to facilitate observations and eliminate loss through 

outflow water. (Note: Finer mesh screen reduces the chances of mysids being lost or becoming impinged, but 

can lead to greater accumulation of debris and the need for additional cleaning.) Upon maturing, gravid 

females are paired with males and isolated in brood cups constructed of 10-cm glass Petri dish bottoms to 

which a 15-cm high cylinder of nylon mesh screen (250-350 μm mesh) is attached. In addition, an appropriate 

test material delivery system is required. The delivery system, test chambers, retention baskets, and brood 

cups should be constructed so that the mysids remain submerged and are not unacceptably stressed by 

crowding or turbulence. The test system used should ensure a good exchange of water between the test 

chambers and retention baskets. A simple overflow drain or similar system that reduces the likelihood of 

impingement as may occur with a self-starting siphon is recommended.

19. Facilities should be well ventilated and free of fumes and disturbances that may affect test organisms. 

Construction materials and equipment that may contact the stock solution, test solution, or dilution water 

should not contain substances that can be leached or dissolved into aqueous solutions in quantities that can 

affect the test results. Construction materials and equipment that contact stock or test solutions should be 

chosen to minimize sorption of test materials. 

20. Test material delivery systems and test tanks should be cleaned using appropriate decontamination 

procedures before each test. Dead brine shrimp and other debris in the test chambers, retention baskets, and 

brood cups should be removed daily. Based on daily observations of water flow through the screens of these 

containers, mysids should be transferred to clean retention baskets or brood cups when water flow is restricted. 

Practice has shown that, in general, mysids require transferring to clean retention chambers and brood cups at 

least weekly.

Range-finding test

21. Preliminary testing is recommended to determine the appropriate concentrations to use in the mysid 

two-generation toxicity test. The form of preliminary testing will depend upon existing toxicological 

information available on the test material. Ideally, the results of a 96-hour toxicity test with mysids would be 

available. If data from an acute test are available, test concentrations are selected where the highest 

concentration in the definitive test is selected to be equal to the lowest concentration that caused adverse

effects in the acute test or 1/5 the LC50 (EC50). The results of the acute toxicity test used to support the 

selection of the chronic test concentrations must be reported along with the results of the definitive test. 

Alternatively, a pared-down life-cycle range-finding test where exposure continues for a period sufficient to 

allow estimation of the appropriate two-generation test concentrations is performed(e.g. 5 breeding pairs at 3 

dose levels + controls carried through a 21 day exposure). The test organisms are exposed to a series of 

widely-spaced concentrations of the test chemical (e.g., 1, 10, 100 mg/L). No replicates are required and 

nominal concentrations of the test material are acceptable. The number of test organisms used, details of 
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observations, and duration of exposure do not have to be as rigorous as for definitive testing. However, the 

range-finding test will be most useful if performed in a manner similar to the intended definitive test. Results 

of range-finding tests, if conducted, must be reported along with the results of the definitive test. 

Definitive test

Experimental design

Test concentrations

22. Normally, five treatment concentrations are used. The highest concentration to be used should be

selected based on existing information or preliminary range-finding tests and should not cause significant acute 

mortality, but should be expected to adversely affect one or more sublethal endpoints. Subsequent 

concentrations/doses used should be stepped down by at least a factor of 2. The use of five test concentrations 

in this fashion not only enables at least some consideration of unexpected dose-response relationships, but 

should provide for sufficient information for the determination of a No Observed Effect Concentration 

(NOEC) or an ECx. 

Controls

23. Every test includes controls consisting of the same dilution water, conditions, procedures, and test 

population, except no test material is added. Carrier (solvent) controls are required if a solvent is used; the 

concentration should be the same in all treatments except the dilution water control.

Replicates and number of test organisms

24. Parental mysids (F0). A minimum of three replicate tanks per treatment are required. The test is 

initiated with 20 newly-released mysid juveniles (< 24 hours old) assigned to reproduction retention baskets 

within each replicate tank. Within the three replicate tanks, one additional retention basket is initiated with 20

newly released mysid juveniles to be subsampled weekly for growth measurements. Upon reaching maturity 

(approximately 13-16 days), a pair consisting of one male and one sexually mature female are randomly 

assigned to separate brood cups within each replicate (with a maximum of 7 m/f pairs possible per replicate). 

Individuals in the reproduction retention baskets not paired in brood cups will be maintained and observed for 

survival and sex determination within the retention baskets until they are paired or until the F0 portion of the 

test is terminated (following release of the second brood or one week after the median day of release of the 

second brood of the controls). Unused mysids from the growth retention baskets may be used to complete the 

male: female pairings when the sex ratio in the reproduction basket is skewed to prevent obtaining 7 pairs. In 

addition, remaining males from the growth retention basket may be used to replace male members of a 

reproductive pair that die prior to the end of the study. In these cases, the additional male must be accounted 

for in survival estimates (see Data Reporting section below). 

25. F1 generation. Offspring from the second brood (F1”) or a combination of the first brood (F1’) and 

second (F1’’) are transferred to their respective test chambers for all treatments (dependent on availability of 

15 young from each treatment on the same day). A “brood” includes all offspring released from a female from 

the release of the first offspring for four days (though typically, all individuals are released within 24 hrs). The 

typical gestational interval is 5 to 9 days, so offspring released more than four days after the beginning of a 

brood release would be considered part of a different brood. The test of the F1 generation is initiated with 15 
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newly-released mysid juveniles (< 24 hours old) assigned to F1 generation reproduction retention baskets 

within a separate tank for each of the F0 exposure conditions. Mixing of young released on the same day, but 

across replicate brood cups, is encouraged to minimize reproduction between siblings. The ages of offspring 

in given baskets should be tracked to know when to take growth measurements (i.e., to know when Day 7 and 

Day 14 are). An additional F1 generation retention basket is initiated with up to 15 newly-released mysid 

juveniles if available within each replicate treatment level to be subsampled weekly for growth measurements. 

Priority is given to filling the reproduction retention baskets first, and then the growth baskets. F1 offspring 

should be randomly placed into chambers designated as reproduction or growth. Subsampling for the growth 

measurements on days 7 and 14 should correspond to the age of the individuals placed in the growth baskets of 

a given replicate and not the initiation of the F1 generation. Upon reaching maturity (approximately 13-16 

days), a pair of one male and one gravid female are randomly assigned to separate F1 generation brood cups 

within each replicate (with a maximum of 7 m/f pairs possible per replicate). Individuals in the F1 generation 

reproduction retention baskets not paired in brood cups will be maintained and observed for survival and sex 

determination within the F1 generation retention baskets until they are paired or until the test is terminated 

(following release of the second brood or one week after the median day of release of the second brood of the 

controls). Unused mysids from the growth retention basket may be used to complete the male:female brood 

cup pairings to obtain seven pairs if the sex ratio in the reproduction basket is skewed. In addition, remaining 

males from the growth retention basket may be used to replace male members of a reproductive pair that die 

prior to the end of the study. In these cases, the additional male must be accounted for in survival estimates 

(see Data Reporting section below). 

Administration of test substance and analytical determination

Exposure via water

26. From a practical perspective, only variations on the aqueous route are appropriate for exposing 

mysids to a test substance. The biggest challenge with water exposure is preparing aqueous solutions of high 

concentration relative to solubility limitations of the test substances in the water (OECD 2000). Organic 

solvents are often used as carriers to assist in delivering a test substance in water. While it is preferred not to 

use a solvent carrier, water exposures can be conducted either with or without a solvent carrier for the test 

chemical of concern. When a chemical is relatively soluble in water (ionic compounds), a solvent is not 

required to enhance water solubility for preparation of stock solutions; however, much of the toxicity testing 

historically conducted with aquatic animals and sparingly soluble nonionic chemicals has utilized carrier 

solvents. 

27. The use of liquid-liquid and solid-liquid saturators to generate solvent-free stock solutions for 

aqueous testing has been reported in recent years, and methods have been described using these approaches to 

test chemicals with widely varying physicochemical properties, including some considered to be very insoluble 

in water (Kahl et al., 1999; Makynen et al, 2000).

28. When the characteristics of the test substance make use of saturators impractical (when the chemical is 

very insoluble, unstable in a saturator system, or expensive/limited in availability) and it is necessary to utilize 

solvents to generate stock solutions for aqueous testing, the recommended solvent carrier is triethylene glycol 

at a concentration ≤ 50 μl/L. Exposure of Americamysis bahia through an entire life cycle to triethylene glycol 

concentrations as high as 1000 mg/l (20,000 times higher than triethylene glycol concentrations recommended 
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in this guideline) had no effect on the survival or reproduction of exposed organisms (Montgomery et al 1985). 

In general, the toxicity of other solvents has not been fully evaluated in chronic tests. Hence, it is essential that 

any test utilizing a carrier solvent, other than triethylene glycol at low μl/L concentrations, include both 

solvent-exposed and non-exposed controls.

Analytical determination

29. Regardless of the exposure technique utilized for this assay, supporting analytical chemistry is 

critical to (i) ensure chemical purity, (ii) document that the test chemical is reaching the mysids, and (iii) 

confirm system performance. In water exposures, concentrations of the (parent) chemical should be measured 

in the stock solution(s) and in each of the test treatments prior to the introduction of test organisms at the start 

of the assay. After test organisms are introduced into the exposure system on Day 0 of the test, and throughout 

the remainder of the exposure period for the F0 mysids, concentrations of the (parent) chemical should be 

measured at least weekly in each of the test treatments. Should this test also expose the F1 generation, 

analytical determination for this generation will follow the procedures described above for the F0 generation. 

Adequate detection and half-life of the parent compound in aquatic media must to be determined before 

initiation of the study to accurately measure exposure concentrations of test chemical.

PERFORMANCE OF THE TEST

Test initiation and conduct

Chemical exposure

30. The exposure portion of the test should not be initiated until all aspects of the delivery system are 

confirmed to have been functioning properly for 48 hours. This includes verification of stable test material 

concentrations and environmental conditions such as temperature, salinity, and dissolved oxygen 

concentrations. The exposure duration for the parental cohort (F0) is approximately a month, with sufficient 

time for healthy females to produce a minimum of two broods. Exposure for the F0 mysids begins when < 24-

hour-old individuals are randomly transferred into the test aquaria from the stock cultures. 

31. At initiation, 20 <24-hour-old individuals are randomly transferred into nylon screen baskets in each 

replicate chamber, such that each treatment group receives a minimum of 60 mysids for use in the 

reproduction portion of the test. An additional 20 mysids are randomly assigned to similar baskets within each 

replicate chamber for use in obtaining growth measurements. Each replicate will contain a total of 40 mysids 

split into two baskets of 20 mysids, one for use in reproduction pairing and one for growth measurements, and 

there will be a minimum of three replicates per treatment. 

32. Fifteen Day 0 mysids are collected from the stock culture and their length determined. These mysids 

are separated into nine groups of five mysids, and then each group is placed on a screen, rinsed in deionized 

water, placed in a pre-weighed aluminum tin, and dried in an oven at 60°C for 48 h. Dried mysid samples are 

kept in a desiccator for at least an additional 48 hours (to allow for cooling of the sample) prior to weighing to 

the nearest 1.0 μg on a microbalance.
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33. The mysids held in both the reproduction and growth baskets are fed newly hatched (< 24-hour-old) 

brine shrimp (Artemia sp.) nauplii ad libitum daily (e.g., at the recommended densities described in Section 

10).

34. At two time intervals (Day 7 and Day 14), mysids are sampled from the growth baskets. On Day 7, 

six mysids are removed from each replicate growth basket and their length determined. These six mysids are 

separated into three groups of two mysids and then each group, placed on a screen, rinsed with deionized 

water, placed in three pre-weighed aluminum tins, and dried in an oven at 60°C for 48 h. On Day 14, the 

remaining mysids (at least three) -- those not sampled at Day 7, those not used to complete reproduction 

pairings, and those not reserved for optional biochemical analyses -- are removed from the growth basket in 

each of the three replicate tanks for all treatment levels and their length determined. Each mysid is then 

individually placed on a screen, rinsed with deionized water, placed in a pre-weighed aluminum tin, and dried 

in an oven at 60°C for 48 h. Dried mysid samples are kept in a desiccator for at least an additional 48 hours (to 

allow for cooling of the sample) prior to weighing to the nearest 1.0 μg on a microbalance. The weight 

observations should be recorded separately for males, females, and immature individuals. Data analyses 

should also be conducted relative to each sex. 

35. When developing embryos can be discerned within an individual female, this ovigerous female is 

paired with one male and the pair is isolated in a separate brood cup within the same replicate chamber. 

Selection of the largest males for placement in the brood cups will reduce the possibility of mistakenly pairing 

the female with an immature female, which would result in a delay of second brood release until after the 

mistake was realized and corrected. Mysids that are not paired should remain in the survival/reproduction 

baskets until only 3 or fewer remain at which time they are transferred to a separate brood cup. 

36. Offspring of the F0 mysids are collected and transferred to aquaria with clean dilution water (for tests 

exposing only the F0 generation) or the same toxicant treatments to which they were exposed during the F0 

generation (for tests exposing mysids through both generations). Care should be taken when transferring 

animals from treatment groups with test chemical to minimize any transfer of test material.

37. Groups of 15 <24-hour-old offspring (F1) from either the first (F1’) or second brood (F1”) of the F0 

mysids are isolated in reproduction baskets (as described in Section 34), which are placed within the F1 tanks 

for the respective exposure conditions of the F0 generation. Mixing of young released on the same day, but 

across replicate chambers, is encouraged to minimize reproduction between siblings. Additional groups of 15 

Day-0 F1 mysids, if available, are randomly assigned to growth baskets within F1 tanks of the same exposure 

treatment of their parents. Leftover Day 0 mysids from each parental exposure condition are collected in 

groups of 5, their length measured, placed on a screen, rinsed with deionized water, placed in pre-weighed 

aluminum tins, and dried in an oven at 60°C for 48 h. Dried mysid samples are kept in a desiccator at least 48 

hours prior to weighing to the nearest 1.0 μg on a microbalance. 

38. The mysids are fed newly hatched (< 24-hour-old) brine shrimp (Artemia sp.) nauplii ad libitum 

(e.g., at the recommended densities described in section 10).

39. At two time intervals for the F1 mysids (Day 7 and Day 14), mysids are sampled from the growth 

baskets. On Day 7, optimally six mysids are removed from each replicate growth basket and their length 

determined. These six mysids are separated into three groups of two mysids and then each group is placed on 

a screen, rinsed with deionized water, placed in three pre-weighed aluminum tins, and dried in an oven at 60°C 

for 48 h. On Day 14, the remaining mysids (at least three) -- those not sampled at Day 7, those not used to 
11

complete reproduction pairings, and those not reserved for optional biochemical analyses -- are removed and 

their length determined. Each mysid is then placed individually on a screen, rinsed with deionized water, 

placed in a pre-weighed aluminum tin, and dried in an oven at 60°C for 48 h. Dried mysid samples are kept in 

a desiccator prior to weighing to the nearest 1.0 μg on a microbalance. The weight observations should be 

recorded separately for males, females, and immature individuals. Data analyses should also be conducted 

relative to each sex. 

40. When developing embryos can be discerned within an individual F1 female, this ovigerous female is 

paired with one male and the pair are isolated in a separate brood cup within the same F1 tank. Selection of 

the largest males for placement in the brood cups will reduce the possibility of mistakenly pairing the female 

with an immature female, which would result in a delay of second brood release until after the mistake was 

realized and corrected. Mysids that are not paired should remain in the reproduction baskets until only 3 or 

fewer remain at which time the are transferred to a separate brood cup identified by replicate within the F1 

tank (receiving clean seawater) for that specific exposure condition. 

41. Offspring of the F1 mysids are enumerated daily until 7 days after the median day of release of the 

second brood (F1”) at which time the test is terminated. 

Observations 

42. Daily assessment of survival in both the growth and reproductive chambers, and reproductive output 

of the reproductive pairs will be made throughout the test. Mortalities will be recorder each day, and when 

possible (i.e. after maturity), the sex of the dead animal will be recorded. If a male member of a reproductive 

pair dies before the second brood is released, he can be replaced by a male from the growth chamber. Survival 

data must be adjusted accordingly (see explanation in data reporting section below). If a female member of a 

reproductive pair dies during the study, she will not be replaced. Mortalities that are clearly non-treatment 

related (e.g. handling accidents) will be distinguished from possible treatment-related mortality (see data 

reporting section and example spreadsheet). The default assumption will be that mortality is due to treatment 

related effects. Daily reproductive output will be recorded to calculate number of offspring/female/d. Unless 

unacceptable water quality excursions and/or disease occur, observed mortality in untreated control animals 

during the chemical exposure phase of the test is generally <25%. In animals exposed to the test chemical, 

overt lethality may occur, particularly in later portions of the assay not reflective of the initial (shorter) rangefinding test.

PERFORMANCE CRITERIA

43. The following criteria are for judging test data acceptability:

• Water quality characteristics should remain within the tolerance limits depicted in Tables 1 and 2;

• There should be documentation (via appropriate analytical chemistry) of purity of the test material, as well 

as delivery of chemical to the test mysids (e.g., concentrations of the chemical in test water);

• There should be at least 70% survival of control animals in all test phases over the duration of the chemical 

exposure.

• At least 75% of the females in the F0 and F1 controls must produce young.

• The average total number of young produced per control female in the first two broods is at least eight.
12

DATA REPORTING

Treatment and interpretation of results

45. Normality can be formally assessed using the Shapiro-Wilk test (Shapiro and Wilk (1965). It was 

assessed from residuals (results of subtracting treatment group means from individual values). Screened 

potential outliers were included in the tests. Outliers can be tested in one generation analyses using Tukey’s 

outlier rule on the untransformed data. Outliers were assessed from residuals (results of subtracting treatment 

group means from individual values) to avoid confounding outliers and treatment effects. Any response more 

than 1.5 times the interquartile range above the third quartile (75th percentile) or below the first quartile (25th

percentile) is considered an outlier by Tukey’s rule. All statistical outliers should be screened to determine if 

there is a non-biological explanation for the outlier response. Unless there is a valid reason for exclusion, 

outliers should be included in data analyses. If data deviate substantially from the assumption of normality, 

data may be transformed (e.g. log transformation, square root transformation, arc sin transformation) and 

retested. If the normality assumption is accepted for either the untransformed or the transformed data 

heterogeneity of variances among the concentration groups was assessed with Levene’s test with absolute 

residuals (Box, 1953). Unless there is a basis for exclusion, screened outlier test should be included in the 

Levene’s tests. If the normality assumption was invalid for both the untransformed and the transformed data 

heterogeneity of variances among the concentration groups was not assessed as the nonparametric procedures 

are appropriate for data analyses. If assumptions of normality and homoscedascity are upheld, data from each 

generation should be analyzed using and analysis of variance (ANOVA) may be used to determine differences 

among treatment and control groups. If one or both tests fail, a nonparametric statistic such as a KruskalWallis test should be used to compare treatment groups. The appropriate multiple comparisons procedure 

should be selected to compare each treatment level to the control (e.g., Dunnett’s procedure for parametric 

data, Dunn’s test for nonparametric data). Mysid generational data should be analyzed according procedures 

followed for each generation and described above to compare the effects in the F0 and F1 generations. 

Comparisons of the F0 and F1 generations can be performed with a two way mixed effects ANOVA model, 

including generation, concentration group, and the interaction of generation and concentration as fixed effects 

and replicate (concentration, generation) as a random effect, allowing unequal variances between the two 

generations. 

46. It is strongly recommended that a statistician be involved in both the design and analysis of the test 

results since the test guideline allows for some variation in experimental design. 

47. Any endpoints that are significantly affected by the test chemical should be reported as such. 

48. Mortality among mating pairs must be distinguished from mating pairs that produced no offspring. 

If a male member of the reproductive pair dies before production of the second brood, he is replaced by a male 

from the growth retention basket if there are sufficient animals. If the female member of the pair dies before 

release of the second brood, she is not replaced and the number of offspring produced for any brood after her 

death should be identified in the data record as “NA” (not applicable) and not included in calculations of 

number of offspring/female. If neither the male or female member of the breeding pair dies, but produce no 

offspring, the number of offspring in the data record should be recorded as 0 (zero).

49. If males from the growth retention basket were used to replace dead males in the reproduction 

chambers, the mortality must be included in the survival calculations (see Annex 4 for more detail).
13

50. Median day of brood release should be based on values from reproductive pairs that survived to 

produce a brood and produced some offspring. 

Test report

51. The test report must include the following:

Name of investigator, laboratory, and dates of test.

Test substance:

- The report must include a detailed description of the test substance, including information on its 

CAS number, source, lot number and purity. 

- Additional information should be provided, when available, such as its solubility in water, 

octanol-water partition coefficient, vapor pressure, toxicity to other aquatic organisms (both 

targeted pests and non-target species), etc.

Test species:

- Information must be provided on the mysids used in the test. If the mysids were field-collected, 

this information must include the location and dates of collection; the salinity and temperature 

conditions at the time of collection, and the acclimation history of the animals when returned to 

the laboratory. If the mysids were purchased, this information must include the dates of shipment 

and receipt, and the supplier’s name and address. If the test mysids were cultured in the 

laboratory, the information must include the original collection location and date, and pertinent 

history of the cultured mysids. Age range of juvenile mysids used to begin the test (within how 

many hours of release by parental female) must be reported. 

- Any observed abnormalities in reproductive behavior or performance of control mysids must also 

be reported.

Test conditions:

- The report must specify the conditions under which the test was performed. These include: 

• information on the source, treatment of, and basic chemical characteristics of the dilution 

water;

• means and ranges for water temperature, salinity, dissolved oxygen concentrations, and pH;

• the photoperiod and light quality used during the exposure;

• the number of replicates and the replicate chamber size; number of females and males per 

replicate;

• information on Artemia used to feed the mysids during the exposure, including supplier and 

lot number, analyses for relevant contaminants (e.g., PCBs, PAHs, and organochlorine 

pesticides) and fatty acids, hydration protocol, and daily feeding regime;

• the basic nature of exposure (i.e., flow-through) in addition to specific information related to 

the exposure type (e.g., whether continuous or intermittent flow-through water delivery type, 
14

flow rate, daily number of volume exchanges of dilution water or water displacement 

percentages over time);

• use of solvent or dispersant if any, the specific solvent or dispersant and the concentrations to 

which the mysids were exposed; the type, manufacturer, and purity of solvent or dispersant; if 

the exposure route was by injection, the carrier and stock infusion rate (μl/hour) and water 

delivery rate (L/hr); and

• the type of controls and the nominal toxicant concentrations; mean and range of toxicant 

concentrations (μl/L or nl/L) for each test treatment and control measured; copies of chemical 

analysis reports.

Results:

- The results must include data for the control, solvent control when used, and treatment-exposed 

mysids. Include the nominal test concentrations, the results of all analyses to determine the 

concentration of the test substance in the test chambers, the recovery efficiency of the method,

and the limit of detection.

- The table of results must include the mean, standard deviation, and range for each test endpoint 

from the replicates employed in the test. Results from appropriate statistical analyses such as an 

ANOVA (parametric) or a Kruskal-Wallis (nonparametric) test of each of the various test 

endpoints across the various treatments and a multiple means comparison test (e.g., Dunnett’s or 

William’s procedure) (Dunnett 1955, 1964; Williams 1971, 1972) that allows statistical 

significance of means should be included. If an ECx is used, a rationale for the “x” value 

chosen, the regression model used, and confidence bounds around the estimate should be 

presented.
15

LITERATURE

(1) Ablett RF and Richards RH. (1980) Suitability of twenty-four-hour and forty-eight-hour unfed 

Artemia as an early foodstuff for ‘0’ group Dover sole (Solea solea L.) production. Aquaculture

19:371-377.

(2) ASTM (2005) Standard guide for conducting life-cycle toxicity tests with saltwater mysids. In: Annual 

book of ASTM standards, Vol. 11.05. American Society for Testing of Materials. E1191-03a. 

Philadelphia, PA.

(3) Dunnett CW (1955) A multiple comparisons procedure for comparing several treatments with a 

control. J Amer Statist Assoc 50:1096-1121.

(4) Dunnett CW (1964) New tables for multiple comparisons with a control. Biometrics 20: 482-491.

(5) Hanaee, J., N. Agh, M. Hanaee, A. Delazar, and S.D. Sarker. 2005. Studies on the Enrichment of

Artemia urmiana Cysts for Improving Fish Food Value. Animal Feed Science and Technology 

120:107-112.

(6) Johns DM, Berry WJ, and Walton W. (1981) International study on Artemia. XVI. Survival, growth 

and reproduction potential of the mysid, Mysidopsis bahia Molenock fed various geographic strains of 

the brine shrimp, Artemia. J Exp Mar Biol Ecol 53:209-219.

(7) Kahl MD, Russom CL, DeFoe DL, Hammermeister DE. (1999) Saturation units for use in aquatic 

bioassays. Chemosphere 39:539-551.

Léger P, Sorgeloos P, Millamena OM, and Simpson KL. (1985) International study on Artemia. 

XXV. Factors determining the nutritional effectiveness of Artemia: The relative impact of chlorinated 

hydrocarbons and essential fatty acids in San Francisco Bay and San Pablo Bay Artemia. J Exp Mar 

Biol Ecol 93:71-82.

(8) Léger P, Bengtson DA, Simpson KL, and Sorgeloos, P. (1986) The use and nutritional value of 

Artemia as a food source. Oceanogr Mar Biol Ann Rev 24:521-623.

(9) Makynen EA, Kahl MD, Jensen KM, Tietge JE, Wells KL, Van Der Kraak G, and Ankley GT. (2000) 

Effects of the mammalian antiandrogen vinclozolin on development and reproduction of the fathead 

minnow (Pimephales promelas). Aquat Toxicol 48:461-475.

(10) McKenney CL, Jr. (1982) Interrelationships between energy metabolism, growth dynamics, and 

reproduction during the life cycle of Mysidopsis bahia as influenced by sublethal endrin exposure. In: 

Physiological Mechanisms of Marine Pollutant Toxicity, WB Vernberg, A. Calabrese, FP Thurberg 

and FJ Vernberg, Eds., Academic Press, New York, pp. 447-476.

(11) McKenney CL, Jr. (1986) Influence of the organophosphate insecticide fenthion on Mysidopsis bahia

exposed during a complete life cycle. I. Survival, reproduction, and age-specific growth. Dis quat 

Org 1:131-139.
16

(12) McKenney CL, Jr. (1987) Optimization of Environmental Factors during the Life Cycle of 

Mysidopsis bahia. Environ Res Brief, EPA/600/M-87/004, U.S. EPA, Cincinnati, OH, 6 p.

(13) McKenney CL, Jr. (1994) Resistance patterns to salinity and temperature in an estuarine mysid 

(Mysidopsis bahia) in relation to its life cycle. Comp Biochem Physiol 109A:199-208.

(14) McKenney CL, Jr. (1996) The combined effects of salinity and temperature on various aspects of the 

reproductive biology of the estuarine mysid, Mysidopsis bahia. Invertebr Reprod Dev 29(1): 9-18.

(15) McKenney CL, Jr. and Celestial DM. (1995) Interactions among salinity, temperature, and age on 

growth of the estuarine mysid Mysidopsis bahia reared in the laboratory through a complete life cycle. 

I. Body mass and age-specific growth rate. J Crust Biol 15:169-178.

(16) McKenney CL, Jr. and Celestial DM. (1996) Modified survival, growth and reproduction in an 

estuarine mysid (Mysidopsis bahia) exposed to a juvenile hormone analogue through a complete life 

cycle. Aquat Toxicol 35(1):11-20.

(17) McKenney CL, Jr. (1998) Physiological dysfunction in estuarine mysids and larval decapods with 

chronic pesticide exposure. In: Microscale Testing in Aquatic Toxicology: Advances, Techniques, and 

Practice, PG Wells, K Lee, and C Blaise, Eds., CRC Press, Boca Raton, FL, Chapter 32, pp. 465-476.

(18) Montgomery RM, Forester J and D’Asaro CN. (1985) Effects of triethylene glycol on Mysidopsis 

bahia (Crustacea: Mysidacea) and Menidia peninsulae (Pisces: Atherinidae). In: Aquatic Toxicology 

and Hazard Assessment: Eighth Symposium, ASTM STP 891, RC Bahner and DJ Hansen, Eds., 

American Society for Testing and Materials, Philadelphia, PA, pp. 270-276.

(19) Nimmo DR, Bahner LH, Rigby RA, Sheppard JM and Wilson AJ, Jr. (1977) Mysidopsis bahia: an 

estuarine species suitable for life-cycle toxicity tests to determine the effects of a pollutant. In: Aquatic 

Toxicology and Hazard Evaluation, ASTM STP 634. FL Mayer and JL Hamelink, Eds., American 

Society for Testing and Materials, Philadelphia, PA, pp. 109-116. 

(20) Nimmo DR, Hamaker TL and Sommers CA. (1978) Entire life cycle toxicity test using mysids 

(Mysidopsis bahia) in flowing water. In: Bioassay Procedures for the Ocean Disposal Permit 

Program, EPA-600/9-78-010, U.S. Environmental Protection Agency, Environmental Research 

Laboratory, Gulf Breeze, FL, pp. 64-68. 

(21) OECD. (2000) Guidance Document on Aquatic Toxicity Testing of Difficult Substances and 

Mixtures. OECD Environmental Health and Safety Publications, Series on Testing and Assessment 

No.23. ENV/JM/MONO(2000)6.

(22) OECD. (2004) Current Approaches in the Statistical Analysis of Ecotoxicity Data: A Guidance to 

Application. Environmental Health and Safety Publications. Series on Testing and Assessment No. 54. 

ENV/JM/MONO(2006)18/ANN. 140pp.

(23) Raimondo S and McKenney CL, Jr. (2005a) Projecting population-level responses of mysids exposed 

to an endocrine disrupting chemical. Integr Comp Biol. 45(1):151-157.
17

(24) Raimondo S and McKenney CL, Jr. (2005b) Projected population-level effects of thiobencarb 

exposure on the mysid, Americamysis bahia, and extinction probability in a concentration-decay 

exposure system. Environ Tox Chem. 24(3):564-572.

(25) Sprague JB. (1969) Review paper: Measurement of pollutant toxicity to fish I. Bioassay methods for 

acute toxicity. Water Res 3:793-821.

(26) Sorgeloos P. (1980) Availability of reference Artemia cysts. Mar Ecol Progr Ser 3:363-364.

(27) Verslycke TA, Fockedey N, McKenney CL, Jr., Roast, SD, Jones, MB, Mees, J and Janssen, CR. 

(2004) Mysid crustaceans as potential test organisms for the evaluation of environmental endocrine 

disruption: a review. Environ Tox Chem 23 (5): IN PRESS.

(28) Williams DA (1971) A test for the differences between treatment means when several dose levels are 

compared with a zero dose control. Biometrics 27: 103-117.

(29) Williams DA (1972) The comparison of several dose levels with a zero dose control. Biometrics 28: 

510-531.
18

ANNEX 1

Table 1. Test Conditions For The Mysid Two-Generation Test Guideline

1. Recommended species Mysid (Americamysis bahia)

2. Test type Continuous or intermittent flow-through

3. Water temperature 26 ± 1oC 

4. Illumination quality Fluorescent bulbs (wide spectrum)

5. Salinity 20 ± 2 o/oo

6. Photoperiod 14 h light, 10 h dark, with 15-30 minute transition period

7. Loading rate Minimum of 30 animals per replicate tank (two baskets with 15 animals/basket)

8. Test replicate chamber size Minimum of 98x15x18 cm 

9. Test replicate solution volume ≈21 liters (when water depth is at its greatest)

10. Volume exchanges of test 

solutions

Provide no less than 90% water replacement in 8-12 hours (Sprague 1969) for 

continuous-flow systems or a minimum of 70% water displacement every 5 hours using 

an intermittent-flow system with self-starting excurrent siphons (McKenney 1986)

11. Age of test organisms at initiation < 24 hours

12. No. of mysids per test vessel F0: Minimum of 40/replicate; 20/retention basket; 2 (1 male & 1 female)/ brood cup

F1: Minimum of 30/replicate; 15/retention basket; 2 (1 male & 1 female)/ brood cup

13. No. of treatments ≥ 5 (plus appropriate controls)

14. No. replicates per treatment ≥3 

15. No. of mysids per test 

concentration (start)

Minimum of 40/replicate; 3 replicates/treatment; 120 mysids per test concentration

16. Feeding regime 24-hour old brine shrimp nauplii at recommended densities (refer to section 10)

17. Aeration None unless DO reaches <60% saturation

18. Dilution water Natural or artificial seawater acceptable to saltwater mysids; uniform quality during test; 

should not affect test outcome; same source as culture water.

If natural, must use 0.25 micron-filtered

Must allow satisfactory survival, growth, and reproduction in controls

If solvent used, < 0.05 ml/L concentration; use solvent controls

19. Exposure period Trans-generational test: 7 days after median day of release of second brood in controls 

(F0 only)

Two-generation test: 7 days after median day of release of second brood in F1 controls

20. Primary endpoints Survival, (F0, F1); 

Growth -length & dry weight, (Days 0, 7 and 14 for F0 and F1);

Time to maturation, (F0, F1)

Time to first brood release, (F0, F1)

Time to second brood release, (F0, F1)

Interbrood duration, (F0, F1)

Number of young per female in each of the first two broods (F0, F1)

Number of total young in the first two broods in each replicate population (F0, F1)

Sex ratio (F0, F1)

Percentage of females that are reproductively active (F0, F1)

21. Optional endpoints Optional biochemical measurements

22. Test acceptability Dissolved oxygen >60% of saturation; mean temperature of 26 ± 1oC; mean salinity of 

20 o/oo S ± 2 o/oo S; ≥70% survival of each generation of mysids in control treatments; 

successful reproduction in at least 75% of control females with an average total of at 

least 8 young in the first two broods
19

ANNEX 2

Table 2. Recommended ranges of water quality characteristics for culturing and testing 

Water characteristic Preferred range Method of measurement

Temperature (oC) 24.0-26.0 Alcohol or electronic thermometer

Dissolved oxygen (mg/L) >4.9 mg/L (>60% saturation) Iodometric or membrane electrode

pH 7.6-8.2 Electronic meter

Salinity 18-22 o/oo S Optical or digital salinometer

If test material is cationic: 

Total organic carbon (mg/L) <5 TOC analyzer
20

ANNEX 3

Mysid Two-generation Test Method Schematic
21

Annex 4:

Table of endpoints

Endpoint Comments

Nominal concentration 

Measured concentration

per tank

Survival (day 0-7) %

per tank

surviving mysids in growth + reproductionchambers

total mysids in growth + reproduction chambers

Survival (day 0-14) %

Per tank

surviving mysids in growth + reproductionchambers

(total in growth − mysids removed for growth measures at day 7) + total reproduction chambers

Survival (0-termination)%

Per tank

surviving mysids in growth + reproductionchambers

(total in growth − mysids removed for growth measures at day 7 and 14 ) + total reproduction chambers

Female mortality %

Per tank

Number of breeding pair females that died

total number of females in all breeding pairs

Male mortality %

Per tank

Number of males that died

total number of males in all breeding pairs

Dry Weight (day 0) μg

per 5 mysids

Dry Weight (day 7) μg

Per 2 mysids

Dry Weight M (day 14)μg

per mysid

Dry Weight F (day 14)μg

per mysid

Dry Weight M (termination)

μg

per mysid

Dry Weight F (termination) 

μg

per mysid

Length (day 0) mm

per mysid

Length (day 7) mm

per mysid
22

Length Male (day 14) mm

per mysid

Length Female (day 14) mm

per mysid

Length M (termination) mm

per mysid

Length F (termination) mm

per mysid

Day of termination

per tank

Median time to maturation 

per tank 

Day when brood pouch is first observed; observation based on reproductive basket only

Median day of 1st brood 

release 

per tank

Days after study initiation; observation based on reproductive basket only

Median day of 2nd brood 

release 

per tank

Days after study initiation; observation based on reproductive basket only

Interbrood duration 

per breeding pair

#offspring/F 1st brooda

per breeding pair

Number of surviving offspring in 1st brood

females in breeding pairs

#offspring/F 2nd brooda 

per breeding pair

Number of surviving offspring in 2nd brood

females in breeding pairs

Total # offspring in first 2 

broods

per breeding pair

Number of surviving offspring in 1st + 2nd broods

females in breeding pairs that survived and produced 2 broods

Total # offspring/ F 

Per tank

Total number of surviving offspring in any brood

all breeding pair females

Percentage of 

reproductively active F

Per tank

number of pairs producing offspring

total females in all breeding pairs

Study day 

per tank (or treatment)

Study day = 0 on the day the treatment cohort is established (and mysids are < 24 hr old)

Pairing day 

per tank

Number of days after initiation of study when reproductive pairs are established
23

Exposure duration (day)

Per tank

Until release of 2nd brood for all treatment groups or 7 days after the release of the 2nd brood of the control 

group

Reproductive days 

Per breeding pair

Day of termination – day of first brood release

# young/F/reproductive day

Per breeding pair

Female sex ratio %a

Per tank

number of F in growth basket + number of F in reproduction basket

Total number of individuals in growth basket + total number of individuals in reproduction basket a Sex ratio is calculated after sex can be determined for individuals in a treatment growth (i.e. after females have developed a 

marsupial pouch)

If there are no offspring for a brood, brood size is recorded as zero if female is still living, and “NA” (recorded as missing) 

for if female died without releasing the brood. 

Percentage of females reproductively active and sex ratio are reported per tank. The other reproductive endpoints are 

reported per mating pair.