IJERD – International Journal of Environmental and Rural Development (2015) 6-2

Research article
erdPeriodic Fertilization Using Urea and Chicken Manure as
Source of Natural Productivity in a Biofloc System during the
Nursery of Pacific White Shrimp Litopenaeus vannamei
MARIA DANESA S. RABIA*
Research, Development and Extension Office
Bohol Island State University, Calape Campus, Calape, Bohol, Philippines
Email: senillo_danesa@yahoo.com

JOMEL G. BAOBAO
Research, Development and Extension Office
Bohol Island State University, Calape Campus

GUILLERMO P. TUTOR
Research, Development and Extension Office
Bohol Island State University, Calape Campus

ERNESTO C. RULIDA
Research, Development and Extension Office
Bohol Island State University, Calape Campus
Received 5 March 2015

Accepted 11 September 2015(*Corresponding Author)

Abstract The effect of periodic fertilization on natural productivity, growth and survival during
the nursery of Litopenaeus vannamei under a zero water exchange set up was investigated.
Nursery culture was carried out for 15 days in 2 m3 indoor concrete tanks with stocking densityof one post larvae (PL)·liter-1 using PL 16 shrimp. Urea and chicken manure were initiallyapplied a week before stocking and added weekly to maintain green water condition. There wasno significant difference in the phytoplankton densities and microbial flocs in the twotreatments. The results demonstrated that the weekly periodic application of urea in a zerowater exchange set up was not viable while fertilization using chicken manure improved feed
conversion rate as well as shrimp survival and production.
Keywords fertilizer, natural productivity, specific growth rate, post larvae

INTRODUCTION
World aquaculture has dramatically grown in the last 50 years. From a production of less than a million
tonnes in the early 1950s, production in 2006 had risen to 51.7 million tonnes excluding aquatic plants(FAO, 2008). In terms of value, shrimp was by far the largest commodity representing 17% of the total
value of international-traded fishery products in 2006 (FAO, 2009). From 2000 to 2005, its global
market had expanded from less than $1 billion to $5.8 billion (FAO, 2008). Since then the increase in
shrimp production has been brought about by so many factors, as it is the intensification of culture
systems. Advancements in aquaculture engineering and biotechnology amongst others have triggered
the transformation from extensive to intensive culture of shrimps. Introduction of new aquaculture
species in certain regions is another major factor. An example is the introduction of the Pacific white
shrimp Litopenaeus vannamei to Asia. In 1996, L. vannamei was introduced on a commercial scale inmainland China and Taiwan and subsequently spreaded to the Philippines and other neighbouring
countries (FAO, 2004).
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However, the intensification of shrimp aquaculture is coupled with pollution, environmental
degradation, and occurrence of diseases caused by heavy effluent discharge and pathogen
contamination of water supply. Thus, reducing waste outputs of shrimp aquaculture operations isessential to ensure a long-term sustainability. According to McIntosh et al., (2001), this could beachieved by improving feed and water management, application of water treatment to wastewater andadoption of zero or minimal water exchange. The latter is the soundest possible option because it does
not only control effluent discharge but also reduces introduction of water borne pathogens byincreasing biosecurity of the cultured organism (Gomez-Jimenez, 2005). The bioflocs technology is an
important discovery in the zero water exchange or closed system of shrimp farming. Bioflocs
technology (BFT) is a system wherein heterotrophic bacteria, algae, and other microorganisms aregrown in flocs controlled conditions within the culture period (Jorand et al., 1995; Avnimelech, 2009).
The microbial biomass or bioflocs utilize dissolved and particulate nitrogenous compounds in thewater coming from the waste of the cultured organism; the assimilation of these compounds is
stimulated by addition of carbon sources to the system (Avnimelech, 1999). The presence of bioflocs
does not only improve water quality but also serves as additional food for the cultured organism. The
BFT represents a sustainable way of producing food by the production of new biomass grown on the
nutrient waste and is used as an alternative food source (Crab et al., 2007). Studies on zero waterexchange during the nursery culture of L. vannamei showed several benefits. Baloi et al., (2010)
reported higher survival of L. vannamei post larvae cultured using reclaimed water from a superintensive zero-water exchange pond in tanks without water exchange for seven days. Widanarni et al.,(2010) demonstrated that the optimum carbon-nitrogen ratio 2:1 using the biofloc technology in L.
vannamei nursery production obtained the best shrimp growth, yield and feed efficiency.
Another strategy to improve sustainability while increasing shrimp production is to promotenatural productivity in the culture system. Natural food production in an aquatic system is enhanced byfertilization. Inorganic and organic fertilizers supply nutrients needed to increase primary productivity
that supports the maintenance of other communities occupying higher trophic levels. Stahl (1979)
reported that natural food alone consisting primarily of a mixture of organic detritus and soil, produced
growth rates in freshwater prawn Macrobrachium rosenbergii post larvae better than commercial
production ponds. Anderson et al., (1987) demonstrated that 53–77% of the growth of juvenile L.
vannamei raised in earthen ponds was due to the assimilation of in situ natural pond biota. PorchasCornejo et al., (2011) reported that promotion of natural feed had a positive effect on weight gain,
survival and final biomass of L. vannamei. Martinez-Cordova et al., (1998) found out that the growthand biomass of L. vannamei were higher in fertilized ponds despite lower feeding rate. L. vannamei
grown extensively (without supplemental feeding) in fertilized ponds resulted to moderate to highsurvival rates (Jaspe et al., 2010). However, research on the use of different fertilizers in a zero waterexchange set up during the nursery of L. vannamei is limited.
OBJECTIVE
This study determined the effects of periodic fertilization on natural productivity, growth and survivalin the nursery of L. vannamei under a zero water exchange set up. Specifically, the following indiceswere measured: water quality – dissolved oxygen, pH, salinity; natural productivity – phytoplankton
and zooplankton count and microbial floc; growth – specific growth rate in terms of weight and length,
feed consumption rate; yield or production – survival.
MATERIALS AND METHODS
Experimental design and set up: The experiment utilized a complete randomized design with twotreatments: inorganic fertilizer (urea) and organic fertilizer (chicken manure). Rearing of L. vanammeiⒸISERD122

IJERD – International Journal of Environmental and Rural Development (2015) 6-2

post larvae lasted for 15 days (from PL 16 to PL 30). It was conducted in the facilities of the Central
Bangus Hatchery located in Pangangan Island, Calape, Bohol. The experiment used six (2 m3) indoor
concrete tanks assigned to the two treatments. The tanks were chlorinated and washed prior, whichwere provided with 7-10 cm mud substrate. Tea seed was added at 100 ppm to eradicate naturally
occurring predators in the mud and lime was applied at 100 ppm subsequently. Chicken manure andurea were applied initially at 1250 kg·ha-1 and 100 kg·ha-1 a week before stocking and added weekly at
a rate of 625 kg·ha-1 and 50 kg·ha-1, respectively to maintain green water condition. Tanks were filledwith seawater with a salinity range of 30-35 ppt. Pond green water was inoculated in the tanks toprovide initial algal population. Each tank was equipped with aeration line to provide sufficientdissolved oxygen level.
Stocking and feeding: L. vannamei post larvae (PL 14) were purchased from a private hatchery (DobeExport International). The shrimps were acclimatized in a ten-tonner rectangular tank with same
salinity and temperature of the hatchery water and were fed to satiation twice a day. Stocking in theexperimental tanks was done early morning on the third day after obtaining the fry at a rate of 1
individual·liter-1. Initial weight and length of the shrimps were 17.85 mg and 1.49 cm. First feeding
was done a day after stocking based on 2.5% body weight. Subsequent feeding was adjusted based on
the actual body weight. Feeding ration was administered four times a day at 8 am, 10 am, 1 pm, and 4pm.
Water quality and natural productivity monitoring: Phytoplankton and microbial-floc population in
the rearing water were monitored weekly and physico-chemical parameters such as temperature,salinity, dissolved oxygen, and pH were checked daily. Temperature and dissolved oxygen wasmeasured using portable DO meter, pH with portable pH meter, and salinity with a refractometer.
Dominant phytoplankton, zooplanktons, and microbial flocs were counted weekly using a standard
haemacytometer under a compound microscope.
Growth and survival monitoring: Weight of the shrimps was monitored weekly to assess growth andadjustment of the feed ration. The shrimps were harvested after 15 days and counted individually. One
hundred (100) representative samples from each tank were weighed using 1.0 g precision electronicbalance and length measured using Vernier caliper to the nearest 0.01 cm. To estimate the specificgrowth rate (SGR), food consumption rate (FCR), and survival rate (SR), the following formulas wereused: SGR = [(ln final weight − ln initial weight) /days] ×100. Where: ln = natural logarithm of final
and initial weight. FCR = weight of feeds consumed/weight gained and SR = (recovered stocks/total
stocks) × 100.
Statistical analysis: To determine significant differences in the water quality parameters, microbial
floc and phytoplankton counts, growth, survival, yield, and FCR between treatments, T-test forindependent sample was used.
RESULTS AND DISCUSSION
Water Quality
Good water quality is essential in the success of shrimp nursery operation. Table 1 shows the minimum,
maximum, and mean levels of these parameters all throughout the duration of the culture period. The
mean daily values recorded during the experiment fall under the optimum range for culture of L.
vannamei. Moreover, the results of all the water quality parameters showed no significant difference
between the two treatments. The mean salinities of the two treatments were at 37.1 ppt and 36.7 ppt,
respectively. Ponce-Palafox et al., (1997) found out that the optimum range for best survival andgrowth of L. vannamei was between 33-40 ppt. Dissolved oxygen is one of the most important waterⒸISERD123

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quality parameters, minimum DO standard for good growth of shrimps is at 3 ppm (Fast and Boyd,
1992). The mean dissolved oxygen concentrations of the two treatments were at 5.0 ppm and 5.1 ppm,
respectively. The temperature readings were relatively stable throughout the culture period in all theexperimental tanks, which fall under the optimum temperature for shrimps at 26°C to 33°C. Mean pH
in the two treatments was at 7.6 and 7.5 with very minimal fluctuation until the end of the experiment.
The recorded pH, fall under the optimum pH in aquaculture systems, at 7.5 to 8.5 values.
Table 1 Dissolve Oxygen, pH, temperature and salinity of water in Pacific white shrimp(L. vannamei) nursery culture with different fertilizers
Treatment/Parameters

Salinity (ppt)
Min

Max

Mean

Dissolved Oxygen

Temperature (oC)

Min

Min

Max

Mean

pH

Max

Mean

Min

Max

Mean

4.8
5.2
5.0a
26.7
29.0
Inorganic Fertilizer (Urea) 33.7 40.0 37.1a
Organic Fertilizer
32.0 39.0
36.7a
4.5
5.7
5.1a
26.4
29.0
(Chicken Manure)
Means with different letters indicate significant differences between treatments (P<0.05).

27.6a

7.6

10.2

8.1a

27.6a

7.5

10.2

7.6a

Phytoplankton and Microbial Flocs
Phytoplankton play a significant role in stabilizing the whole pond ecosystem and in minimizing thefluctuations of water quality. A suitable phytoplankton population enriches the system with oxygen
through photosynthesis during day light hours and lowers the levels of CO2, NH3, NO2, and H2S.
During the first week of the experiment there was no significant difference in the phytoplankton
densities between the two treatments (Table 2). Common phytoplankton observed were diatoms and
Chaetoceros species. A day after the 3rd fertilization, the algae bloomed, manifested by dark green
coloration of the water in the tanks applied with urea. Mean phytoplankton count in these tanks
increased from 372,500 + 2,500 cells·ml-1 to 513,333 + 11,273 cells·ml-1 and was significantly higher
compared to the tanks fertilized with chicken manure. Generally, the phytoplankton densities all
throughout the experiment were relatively low compared to the healthy phytoplankton abundance
reported by Cordova et al. (1998) in ponds applied with organic and inorganic fertilizer at 530,000980,000 cells·m-1. The denseness could be attributed to the use filtered seawater. Pond green water was
only added in the tanks to provide initial algal population.
Phytoplankton aggregates with microorganisms in the aquaculture system to form microbial flocs.
Bio-flocs or the microbial flocs are a mixture of microorganisms (bacteria, phytoplankton, andzooplankton), algae, and other particles (Jorand et al., 1995). Typical flocs are irregular by shape, havea broad distribution of particle sizes, which are fine, easily compressible, highly porous, and permeable
to fluids (Lee Chen, 2004). Microbial floc or flocculated particles were observed to be increasing as
shown in Table 2. The build-up rates of the floc on the 2nd week followed the standard community
succession principle wherein from a clear water condition, algal bloom follows, and bacterial
communities are established when the water turns to brown. Build up of flocculated particles in the two
week time was relatively low.
The microbial flocs observed in the experiment were visibly large and distinct under the
microscope. Optimum water quality conditions were important in maintaining healthy population of
microbial flocs and these were met during the experiment. High dissolved oxygen in the system was
not only essential for the shrimps but also for the metabolic activity of the cells and structure of the
microbial flocs. A trend towards larger and more compact flocs at higher dissolved oxygen
concentrations was noted by Wilen and Balmer (1999). Temperature was also important in microbial
floc morphology. Krishna and Van Loosdrecht (1999) observed that higher temperatures (30-35°C)
resulted in bulking of the sludge due to the excessive production of extracellular polysaccharide, thusintermediate water temperature of 20-25°C would be best to obtain stable microbial flocs. Similarly,ⒸISERD124

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pH has an effect on microbial floc; according to Mikkelsen et al., (1996) changes in pH determine thestability of bio-flocs present in the system.
Table 2 Mean phytoplankton and microbial floc count in the water of Pacific white shrimp(L.vannamei) nursery culture with different fertilizers
Treatment
Inorganic Fertilizer (Urea)

Phytoplanktons (cell density ml-1)
Initial
Day 7
372,500 + 2,500 a
513,333+ 11,273a

Microbial Flocs (cell density ml-1)
InitialDay 7
723 + 13a
797+ 17a

Organic Fertilizer (Chicken Manure) 365,833 + 3,819 a
423,333 + 3819 b
732 + 38a
Means with different letters indicate significant differences between treatments (P<0.05).

836+ 15a

Growth and Survival
A day after the 3rd fertilization, the algae bloomed in the tanks applied with urea which resulted to massmortality of all stocks. However, the fatality could not be attributed to the increase in phytoplankton
density because it was relatively lower compared to a healthy phytoplankton bloom (Cordova et al.,1998). Furthermore, dissolved oxygen remained at its optimum level and apparently was not the causeof mortality. One possible reasons of the fatality could be the increase of NH3 in the system triggeredby the addition of urea. In the experiment conducted by Das et al., (2005) application of organic andinorganic fertilizer increased inorganic nutrients including ammonia. Application of inorganic fertilizer
gave peak values of nitrogen species such as ammonia, nitrite and nitrate earlier during first to second
week. Although natural food production was enhanced by applying organic and inorganic fertilizers,
the results showed that weekly application of urea at 50 kg·ha-1 significantly affected survival, causingmass mortality of stocks. On the other hand, survival of shrimps in tanks fertilized with chicken
manure was 92.68%; with specific growth rate (%·day-1) of 14.05 in terms of weight and 18.17 interms of length and total yield of 128.37 g·m-1. Lara-Anguiano et al., (2013) found out that L.
vannamei culture in tanks with zero water exchange using organic fertilizer (molasses) had higher
survival and production rates and reduced ammonia concentrations toward the end of the experiment
while the use of inorganic fertilizer caused increased nitrogen and phosphorus.
CONCLUSION
Periodic fertilization using chicken manure at a rate of 625 kg·ha-1 improved feed conversion rate aswell as shrimp survival and production within this experiment. Moreover, the results indicate thatweekly periodic application of urea at a rate of 50 kg·ha-1 without any water replacement in tanks
during the nursery of L. vannamei is not viable.
RECOMMENDATIONS
Further studies should design experiments that include the measurement of other water quality
parameters such as NH3, nitrites, nitrates, total suspended solids, and microbial evaluation such as total
plate count and Vibrio count. It is also very interesting to determine the density of the zooplankton in
the water vis-à-vis the feeding incidence.
ACKNOWLEDGMENT
We would like to express our sincerest gratitude to Engr. Ramon Alegre of DOBE Export International
for free Vannamei fingerlings; Mr. Dionisio Colantro for the use of facility of Central Bangus HatcheryⒸISERD125

IJERD – International Journal of Environmental and Rural Development (2015) 6-2

at Barangay Lawis, Pangangan Island, Calape; 4th year BS Fisheries students for the assistance of theexperiment.
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