bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and application of a bioenergetics model for juvenile walleye Pollock
Authors: Ciannelli L. , Drodeur R. D. , Buckley T. W.
Published: April 2005

A bioenergetics model was parameterized for age‐0 walleye pollock, Theragra chalcogramma, based on a synthesis of literature data. The sensitivity of the new parameters was tested by individual parameter perturbation (IPP) analysis. The model was applied to estimate individual and total cohort food consumption of age‐0 pollock in two areas of high pollock density in the Gulf of Alaska during the summer of 1990. Total cohort consumption was compared with zooplankton biomass and production estimates for the same areas and times of the year. The model was also used to examine the bioenergetic implications of age‐0 pollock diel vertical migration through a thermal gradient. During a 1‐month bioenergetics simulation, individual daily consumption decreased from 16·0 to 6·0% of wet body weight. Daily ration estimates corresponded well with independent field estimates of daily ration for the same areas and time of the year. Comparison of total cohort consumption with prey availability (production and biomass) indicated minimal potential for food limitation. Bioenergetic optimization of growth can be a potential benefit of diel vertical migration to age‐0 pollock, however more information on prey density and distribution is needed to test this hypothesis thoroughly.
Sex‐biased marine survival and growth in a population of coho salmon
Authors: Spidle A. P. , Puinn T. P. , Bentzen P.
Published: April 2005

Examination of historical records for coho salmon in Big Beef Creek, in western Washington, U.S.A., indicated that more adult males than females returned to spawn, and that the mean length of the females exceeded that of males. Sex‐biased survival and faster growth among females are unusual among salmonids but precedented in some other coho salmon populations. To help determine the stage of life at which sex‐biased mortality might occur, the sex‐linked GH‐ψH pseudogene was used to determine the sex of smolts emigrating from Big Beef Creek in 1995–1997. In each of the 3 years the sex ratio was indistinguishable from 50:50, indicating similar survival rates in fresh water, and implying that the male and female coho salmon follow different foraging strategies when they are at sea. The female strategy apparently results in greater mortality, but benefits survivors with greater size. The male strategy appears to allow greater survival at the cost of reduced size.
Abundance, distribution, reproduction and diet of notacanthid fishes from the north‐east Atlantic
Authors: Coggan R. A. , Gordon J. D. M. , Merrett N. R.
Published: April 2005

Notacanthid fishes were among the 10 most abundant species sampled in research surveys using fine meshed trawls fished to depths of 3000 m in the Rockall Trough and 4500 m in the Porcupine Seabight between 1975 and 1992. Two species, Noctacanthus bonapartei and Polyacanthonotus rissoanus, were dominant but their population structure and certain aspects of morphometric and reproductive biology differed between the two sampling areas. In general, sex ratios were skewed in favour of females, size increased with depth and male and immature individuals were restricted to shallower depth zones. Fecundity was highly correlated with total weight and showed a positive relationship with species' size. Ovaries contained two batches of eggs and the spawning season was protracted, occurring mostly over winter months. Dietary studies showed a dependence on benthic macro fauna though the two dominant species have different dentition and exploit different trophic niches. In the Rockall Trough, peak abundances for N. bonapartei and P. rissoanus occurred in the 750 m and 1250 m zones, respectively, lying within the depth range currently exploited by commercial deep‐water trawls (600–1400 m). The probable impacts of commercial operations on notacanthid fishes are discussed.
Growth, consumption, and productivity of the California killifish in Ojo de Liebre Lagoon, Mexico
Authors: Péarez‐Españta H. , Galváaan‐Magañta F. , Abitia‐Cáardenas L. A.
Published: April 2005

The growth curve of the California killifish Fundulus parvipinnis was estimated from length–frequency data using FiSAT software. The population structure was calculated and was extrapolated over the total area of the lagoon to estimate the total biomass. Using published data of oxygen consumption and ancillary data, the consumption of food by killifish was also estimated. Production of the species was via the first derivative of the von BertalanVy growth curve. This approach is proposed for other species whose biology is described in the literature.
Do random fluctuations in daily ration affect the growth rate of juvenile three‐spined sticklebacks?
Authors: Ali M. , Przybylski M. , Wootton R. J.
Published: April 2005

The effect of random fluctuations in daily ration on the growth performance of individual juvenile three‐spined sticklebacks Gasterosteus aculeatus was studied in experiments lasting 21 days at 14°C and a photoperiod of 10L:14D. Two mean ration levels were used: a maintenance ration of 2%, and a high ration of 6% of initial body weight per day. For experimental fish, the daily ration varied randomly about the required mean value with a coefficient of variation of 33%. The controls received a constant daily ration. The experiment was replicated in winter (Dec.‐Jan.) and spring (Mar.‐Apr.). At a given ration, there was no significant difference between the specific growth rates of fish receiving constant or varying ration. Neither the final dry weight, final body water content nor final lipid content (% dry weight) differed significantly. As expected, ration had a significant effect on growth rate, final dry weight and body lipid and water content. There was a significant difference in mean growth rate between the winter and spring replicates. The growth rates observed in these experiments were compared with those predicted from a previously described empirical growth model developed for sticklebacks fed constant rations. The model underestimated mean growth rates.
Circadian rhythms of demand‐feeding and locomotor activity in rainbow trout
Authors: Sánchez‐Vázquez F. J. , Tabata M.
Published: April 2005

Under free‐running conditions, most rainbow trout displayed circadian feeding rhythms, although the expression of circadian rhythmicity depended on the experimental condition: 16·7% of fish under constant dim light (LL dim), 66·1% under a 45 :45 min light‐dark cycle (LD pulses), and 83·8% under constant light (LL). Under LD pulses, the period length of the free‐running rhythms for feeding was significantly shorter (21·9 ± 0·7 h, n=8) than under LL (26·2 ± 0·3 h, n=10). Period length for locomotor activity under LL was 25·8 ± 0·6 h (n=4). Under LD conditions, the daily demand‐feeding profile was always confined to the light phase and chiefly composed of two main episodes, directly after lights on (light elicited) and in anticipation to lights off (endogenous). Contrasting to feeding, the diel locomotor activity profile varied remarkably: a diurnal activity pattern at the bottom, while a clearly nocturnal pattern at the surface. These results contribute to a better understanding of feeding and locomotor rhythms of rainbow trout, providing evidence for the existence of a biological clock involved in their circadian control. This finding contrasts with the previously recorded lack of an endogenous oscillator in the pineal organ driving the rhythmic secretion of melatonin, which suggests different locations from the pineal for the circadian pacemakers in this species.
Radioactive strontium (85Sr) in marking newly hatched pike and success of stocking
Authors: Vuorinen P. J. , Nyberg K. , Lehtonen H.
Published: April 2005

Immersion of newly hatched pike fry in an aqueous solution of 1·85 MBq ml−185Sr did not affect their growth or survival over 3 weeks. Cannibal pike fry retained only l.2–3·3% of the 85Sr from their labelled prey. Newly hatched 85Sr‐marked fry stocked into two lakes in 3 years were distinguishable from wild fish 4–6 weeks later. Stocked and wild fry grew equally well, and stocked pike survived best where density of wild pike was highest. There was no evidence of increase in density as a result of Stocking.
The relative abundance of brown trout in acidic softwater lakes in relation to water quality in tributary streams
Authors: Hesthagen T. , Jonsson B.
Published: April 2005

The influence of the water quality of tributary streams on the relative abundance in benthic gillnet catches (catch per unit effort, cpue) of allopatric brownSalmo truttawas assessed in associated acidic, softwater lakes. The study was carried out over 6 years (1989–1994) in 15 lakes located at altitudes between 230–715 m a.s.l. in two Norwegian catchments. The water quality of the main inlets and outlets varied little, as indicated by their of pH range (4·93–5·51) and calcium concentrations (0·19–0·44 mg 1−1), but varied more with respect to concentrations of inorganic, monomeric aluminium (7·0–41·0 μg l−1). Most of the lakes were also fed by secondary streams with better water quality: a maximum pH of 6·56, calcium levels of up to 0·74mg 1−1, and inorganic aluminium levels as low as l·0 μg 1−1. The cpue was inversely correlated with lake altitude (r2=0·50), and thus was adjusted to a mean altitude. The calcium concentration in the richest secondary stream to each lake, its richness judged on the basis of its acid‐neutralizing capacity, had the highest predictive power of the variability in cpue (r2=0·49).The calcium content in the other secondary streams or in the main inlets and outlets did not correlate with cpue. Alkalinity in the main outlets correlated to some extent with cpue (r2=0·27). It is suggested that secondary streams with good water quality provide important refuges for the recruitment of brown trout in acidic softwater lakes.
Effect of feeding time on postprandial nitrogen excretion and energy expenditure in rainbow trout
Authors: Gélineu A. , Médale F. , Boujard T.
Published: April 2005

The effect of feeding time (dawn or midnight) on nitrogen excretion and energy expenditure was studied in immature rainbow trout using measurements of respiratory gas exchange. Fish (mean individual weight 70 g) were maintained indoors under natural photoperiod and fed by hand (commercial food pellets) at a rate of 1% weight/day−1. Rates of ammonia and CO2excretion and O2uptake were measured every hour. Ammonia excretion increased immediately after feeding in fish fed at midnight, and 2h after feeding in fish fed at dawn. Ammonia excretion and energy supply from protein catabolism, were higher in trout fed at midnight than in those fed at dawn, while total energy expenditure was the same in both groups. The results suggested that trout fed in phase with their natural feeding rhythm use dietary protein more efficiently for growth than do trout fed out of phase with the natural rhythm.
Population structure of Atlantic salmon from the Conne River, Newfoundland as determined from microsatellite DNA
Authors: Beacham T. D. , Dempson J. B.
Published: April 2005

Variation at four microsatellite loci was examined for three populations of Atlantic salmon Salmo salar from the Conne River, Newfoundland. Samples of wild parr were collected from the mainstem Conne River during 4 years, and from tributaries Twillick Brook and Bernard Brook during 2 years. No significant temporal variation was observed in allele frequencies at the Ssal4, Ssal97, Ssa202, and Ssa289 loci. No difference in allele frequencies was observed between parr from Bernard and Twillick brooks at any locus, but allele frequencies of mainstem Conne River parr were significantly different from those of the tributaries at Ssal4 and Ssa202, indicative of differentiation among local populations. Atlantic salmon from the Conne River system were well differentiated from those in Nova Scotia, Canada and from those in Europe.
Genetic and morphological variation in a common European cyprinid, Leuciscus cephalus within and across Central European drainages
Authors: Hänfling B. , Brandl R.
Published: April 2005

Genetic variability and differentiation of the common European cyprinid Leusciscus cephalus was investigated within and across the drainages of the rivers Rhine, Elbe and Danube using starch gel electrophoresis and morphological characters. Eleven of 24 presumptive enzyme loci showed some allozymic variation. Compared to other freshwater fish, genetic variability within all sites was high (He=0·074–0·113). This was explained by the wide geographical and ecological range of the chub. In contrast, genetic and morphological differentiation between sites and drainages was low (FST=0·15), which may be due to the high dispersal ability of the chub and translocations of spawn by waterfowl. The phylogeographic structure of Leuciscus cephalus in north‐eastern Bavaria showed low congruence with Cottus gobio populations sampled in the same area.
Sperm motility of the marine teleosts Boops boops, Diplodus sargus, Mullus barbatus and Trachurus mediterraneus
Authors: Lahnsteiner F. , Patzner R. A.
Published: April 2005

The spermatozoa of Boops boops, Diplodus sargus, Mullus barbatus, and Trachurus mediterraneus were motile in sea water, and in electrolyte solutions (NaCl) and non‐electrolyte solutions (glucose) with an osmolality of 600–1000 mosmol kg−1. Their mean motility rate 10 s after initiation was about 80%, while about 10% of the motile spermatozoa moved non‐linearly, 45% linearly, and 45% circularly. The average path swimming velocity was significantly higher in M. barbatus (about 90 μm s−1) than in the other species (70 μm s−1). The number of motile spermatozoa decreased to 0% within 50 s after initiation of motility in T. mediterraneus, within 90 s in M. barbatus . In B. boops and D. sargus about 90% of the spermatozoa stopped movement during the first 90 s of the motility period, while the rest remained motile for 2–3 h. Motility of B. boops and D. sargus spermatozoa was reversibly suppressed in the seminal plasma, and in electrolyte and non‐electrolyte solutions of 100–200 mosmol kg−1. The trigger for motility activation was hyperosmolality (700–1000 mosmol kg−1). Motility of M. barbatus and T. mediterraneus sperm was only partly suppressed in the seminal plasma since freshly collected semen contained about 25–50% locally motile spermatozoa. When sperm was activated immediately after collection with electrolyte and non‐electrolyte solutions of 700–1000 mosmol kg−1 spermatozoa moved progressively. The motility of those spermatozoa which had not yet been motile after collection was completely and reversibly suppressed in M. barbatus at osmolalities of 1200 mosmol kg−1, and at osmolalities of 100–200 mosmol kg−1 in T. mediterraneus . Therefore two triggers were necessary for initiation of motility. The nature of the first trigger was uncertain, the second trigger was a switch to hypoosmolality in M. barbatus and to hyperosmolality in T. mediterraneus . The sperm organisation of B. boops, D. sargus, M. barbatus and T. mediterraneus revealed species‐specific parameters which could not be related with the sperm motility behaviour.
The effect of ration level and social rank on the development of fin damage in juvenile rainbow trout
Authors: Moutou K. A. , McCarthy I. D. , Houlihan D. F.
Published: April 2005

The development and severity of fin damage was examined in groups of juvenile rainbow trout Oncorhynchus mykiss of different strength of feeding hierarchies. The development of dorsal and caudal fin damage over time was compared between four groups fed different ration levels (0·25, 0·5, 1·0 and 1·5% body weight day−1) and between individuals of different feeding rank within each group. Dominance hierarchies were assessed from repeated daily measurements of food consumption of individuals using radiography. The feeding and growth data indicated that the strength of the social hierarchy weakened with increasing ration. Caudal fin damage developed with time in all groups whereas dorsal fin damage developed only under limited rations. The severity of both dorsal and caudal fin damage was significantly dependent on the ration size fed to the group, with lower ration groups sustaining more fin damage. The severity of dorsal fin erosion was greater than for the caudal fin. Within the two lower ration groups, subordinate fish suffered the most dorsal fin damage. The results suggested that the severity of dorsal fin damage within groups of juvenile rainbow trout can be used as an indicator of hierarchy Strength.
Morphological variation in the catadromous Australian bass, from seven geographically distinct riverine drainages
Authors: Jerry D. R. , Cairns S. C.
Published: April 2005

The Australian bass Macquaria novemaculeata is a catadromous species restricted to coastal drainages of south‐eastern Australia and recently has undergone reductions in population numbers. Morphometric variation among bass from seven distinct drainages was used to test for the presence of stock structuring. Males and females were treated separately. For both male and female bass, significant heterogeneity in morphology among sample locales was revealed by univariate statistics and discriminant function analysis, with morphological variation found to differ in a clinal pattern. The demonstration of population‐specific morphological traits among bass from different river drainages may indicate that inter‐populational movement is restricted and that each sample locale constitutes a separate stock of bass.
Enlarged fatty livers of small juvenile cod: a comparison of laboratory‐cultured and wild juveniles
Authors: Grant S. M. , Arown J. A. , Boyce D. L.
Published: April 2005

Large juveniles and adult cod Gadus morhua develop enlarged fatty livers when fed high‐energy lipid‐rich diets in captivity; however, little is known of the partitioning of growth energy of small juveniles. This study compared simple indices of condition of laboratory‐cultured and wild juvenile cod of similar size that consumed high‐energy, lipid‐rich food to determine whether small juveniles develop enlarged fatty livers in captivity. Cultured cod developed enlarged fatty livers. The hepatosomatic index (IH) and condition factor of cultured cod were significantly higher and tissue water contents were significantly lower than in wild cod. Cultured cod also exhibited significantly higher muscle mass at length. Cod of similar age exhibited a high range in body size, high coeficient of variation in size and the IH was correlated positively with body size indicating that a size‐selective social hierarchy had developed in the laboratory. In contrast, the IH of wild cod was correlated negatively with body size, supplying evidence of high utilization of dietary lipids by larger juveniles in association with increased metabolic expenditure when feeding on small prey items.
Mating tactics and male‐male courtship in the lek‐breeding cichlid Oreochromis mossambicus
Authors: Oliveira R. F. , Almada V. C.
Published: April 2005

Data are presented on the breeding behaviour of Oreochromis mossambicus under captive conditions. Males tended to synchronize their occupation of territories and breeding activities. Different male mating tactics were observed, namely establishing a breeding territory, acting as a floater, or behaving as a sneaker. The majority of spawnings observed involved dominant males and were subjected to interference from other males. Males were found to court other males that frequently responded to these attempts by adopting a female‐like behaviour. Results are discussed in terms of a probable time constraint in territoriality, which promotes male‐male competition and a low level of sex discrimination by territorial fish.
Movement and pattern of activity of the roach in the River Spree, Germany
Authors: Baade U. , Fredrich F.
Published: April 2005

Water body and bank structure use of adult roach Rutilus rutilus were examined to increase the knowledge of the most abundant species in the River Spree, Germany. Six tracking series were conducted between 1994 and 1995 to analyse the seasonal and diel movements of the fish. In each series, four to 12 roach were tagged externally and located every 2 h for up to 14 days using radiotelemetry. Roach were highly active, moving up to 10 km downstream to Lake Dämeritzsee, and up to 6 km upstream from their release site. The fish, which mostly swam greater distances upstream during the day and downstream at night, were most active during the spawning season. Their habitat range varied greatly. Close‐range habitat, based on 50% of all radiolocations, varied between 5 and 1350 m (mean, X̄=296 m). Wide‐range habitat, based on 90% of all radiolocations, varied between 75 and 3820 m (X̄=1006 m). The fish preferred different sections of water at different times of year, casting doubt on the relevance of the term home range. Generally, roach stayed close to the bank structures of the main channel during the day and moved to the stagnant waters at night. Consequently, they were most active at dawn and dusk.
The effect of sexual maturation on the spatial distribution of Baltic salmon
Authors: McKinnell S. , Lundqvist H.
Published: April 2005

This study examines the migratory habits of tagged mature and immature Atlantic salmon parr Salmo salar released from the Norrfors hatchery on the River Umeälven, Sweden from 1975 to 1977 and 1988 to 1990. Tags were recaptured in the Baltic Main Basin, the Gulf of Bothnia, and in the Umeälven. Ninety‐three per cent of previously mature males were recovered in the Umeälven compared with 23% of the previously immature smolts during the calendar year of release. In the second year after release (grilse year), the proportion of early maturing males recovered in the Umeälven was significantly greater than the proportion of previously immature smolts recovered in the Umeälven. Likewise, the proportion of previously mature males recovered in the Main Basin was significantly less than the proportion of previously immature smolts recovered in the Main Basin in the second calendar year after release. Previously mature males rematured after fewer years at sea, on average, than the previously immature smolts. Following the second calendar year after release, the proportions of previously mature males and previously immature smolts were not significantly different throughout the Baltic Sea.
Trophic polymorphism amongst Arctic charr from Loch Rannoch, Scotland
Authors: Adams C. E. , Fraser D. , Huntingford F. A. , Greer R. B. , Askew C. M. , Walker A. F.
Published: April 2005

This paper describes the results of a multivariate and univariate morphometric analysis of three groups of Arctic charr Salvelinus alpinus from Loch Rannoch, Perthshire, Scotland, distinguished a priori on the basis of coloration (bright v. cryptic) and site of capture (from two locations 12 km apart). The analysis produced a clear and highly significant distinction, not only between brightly and cryptically coloured charr, but also between the two cryptically coloured groups, one of which was more robust in terms of several size‐independent head measurements. Stomach analysis showed that the brightly coloured charr fed entirely on zooplankton, the less robust, cryptically coloured fish, fed on benthic macroinvertebrates, whereas a significant proportion of the diet of the more robust cryptically‐coloured form consisted of other fish. Differences in length at age also distinguished the three forms, with the robust, piscivorous charr, which live longer and potentially reach a larger final size, attaining smaller sizes at a given age. These data clearly confirm the previous identification of a distinct planktivorous morph of Arctic charr in Loch Rannoch and extend the morph analysis by distinguishing two additional morphs, a benthivorous morph and a piscivorous morph that are morphologically and ecologically distinct. The results are discussed in the context of other systems in which sympatric morphs of Arctic charr have been described.
Effects of senescence and density on the aggression of adult female sockeye salmon
Authors: Quinn T. P. , McPhee M. V.
Published: April 2005

Aggression of individual female sockeye salmon Oncorhynchus nerka in Hansen Creek, Alaska, was unrelated to body size or density but it decreased over the last 7 days of life from an average of 8·89–1·47 counts 15 min−1. In addition, as females neared death they tended to use less violent forms of aggression.
First record for the European Ichthyofauna of Dentex (Cheimerius) canariensis Steindachner, 1881
Authors: Otero J. G. , Galeote M. D. , Arias A.
Published: April 2005

Dentex (Cheimerius) canariensis is recorded for the first time for European waters, on the basis of four specimens captured on the coast of Cádiz (SW Iberian peninsula).
Histological classification of oocyte growth and the dynamics of ovarian recrudescence in Tilapia zillii
Authors: Coward K. , Bromage N. R.
Published: April 2005

Serum levels of 17β‐oestradiol and testosterone peaked and fell within 6 days of spawning in Tilapia zillii suggesting that vitellogenic growth began as early as day 2 or 3 postspawning. As early as day 8, stage 6/7 (late nitellogenic and maturing) oocytes occupied 60–70% of the ovary. From day 8 onwards the proportion of stage 6/7 oocytes changed little, though IG increased (as oocytes grew) to reach maximal levels of ∼ 5·5% by day 14. IG was correlated significantly to the proportion of stage 6/7 oocytes. Postovulatory follicles were observed immediately following spawning occupying up to ∼ 7% of the ovary but were not present from day 3 onwards. Atretic oocytes were found throughout the time period monitored (generally occupying <2% of the ovary) but were more prevalent from day 18 onwards. Data suggest that previtellogenic oocytes are recruited into vitellogenic growth immediately after spawning and can complete vitellogenesis as early as day 8 postspawning. Knowledge of this timing is likely to be important in the development of spawning induction programmes in T. zillii and other related species.
Fine structure of the intestine development in cultured sea bream larvae
Authors: Calzada A. , Medina A. , de Canales M. L. González
Published: April 2005

At hatching, the gut cells of Sparus aurata are quite undifferentiated; however, slight ultrastructural differences can already be distinguished between the presumptive intestinal regions. The hindgut cells are more differentiated than midgut cells and the rectal cells show rather particular ultrastructural features. During days 1 (D1) and 2 (D2) after hatching, major changes occur that lead to full differentiation of the epithelial cells. Shortly before the onset of exogenous feeding (D3), the anterior intestine enterocytes can synthesize lipoprotein particles (LP) from endogenous lipids. The posterior intestine enterocytes show morphological features indicating a role in absorption and intracellular digestion of nutrients, whereas the rectal cells do not. Transient ciliated cells occur at hatching (D0) in the presumptive intestine, except in the caudal rectum, and disappear at the start of the late endotrophic phase about 3 days after hatching (D3). At hatching, very scarce enteroendocrine and leucocyte‐like cells are found at the base of the gut epithelium. Their number increases throughout development. At D3 (late endotrophic phase), LP synthesized mainly in the periblast invade the circulatory system, interstitial spaces of the subepithelial tissue and intercellular spaces of the gut epithelium. When the endo‐exotrophic phase begins (D4), the enterocytes can absorb exogenous food. Acid phosphatase activity was detected in microvilli, pical vacuoles and Golgi complex in both anterior and posterior enterocytes, as well as in supranuclear vacuoles (SNV) of posterior enterocytes, but not in the apical tubulovesicular system (TVS). During the exotrophic phase, large lipid droplets (LD) are found in anterior enterocytes, and the SNV occupy a large cell volume in posterior enterocytes. LP accumulate first in extracellular spaces and then are transferred to the circulatory system. Mucous and rodlet cells appear in the intestinal epithelium during the exotrophic phase, from D15.
Energy savings in sea bass swimming in a school: measurements of tail beat frequency and oxygen consumption at different swimming speeds
Authors: Herskin J. , Steffensen J. F.
Published: April 2005

Tail beat frequency of sea bass, Dicentrarchus labrax (L.) (23.5 ± 0·5 cm, LT), swimming at the front of a school was significantly higher than when swimming at the rear, for all water velocities tested from 14·8 to 32 cm s−1. The logarithm of oxygen consumption rate, and the tail beat frequency of solitary swimming sea bass (28·8 ± 0·4 cm, LT), were each correlated linearly with swimming speed, and also with one another. The tail beat frequency of individual fish was 9–14% lower when at the rear of a school than when at the front, corresponding to a 9–23% reduction in oxygen consumption rate.
Spatiotemporal variation in the population structure of the European hake in the NW Mediterranean
Authors: Recasens L. , Lombarte A. , Morales‐Nin B. , Tores G. J.
Published: April 2005

The bathymetric distribution of Merluccius merluccius was studied as a function of length, age and maturity of specimens caught by commercial trawl and longline in Different seasons. Males matured first at 28·8 cm (3 years old), and females at 38·0 cm (3·5 years old). Reproductive activity was noted practically throughout the year with its most pronounced spawning peak in the autumn. Most fish <37–40 cm were males and >46 cm were females. Specimens occurred between 50 and 750 m depth, although density was low at >400 m. Adults were found at all depth strata studied. Recruits and juveniles were limited to inshore waters <400 m, most were found between 100 and 200 m. Spring and summer were the preferred seasons for recruitment; although for both seasons there was some interannual variation. Adult distribution also varied, according to the season. Young adults were spread over the entire depth range, with the biggest ones concentrated at the edge of the shelf (150–350 m), especially in autumn and winter. The main spawning peak coincided with this concentration of adults suggesting that spawning occurred in autumn/winter at the edge of the shelf.
The minimum effective spermatozoa : egg ratio for artificial insemination and the effects of mercury on sperm motility and fertilization ability in Clarias gariepinus
Authors: Rurangwa E. , Roelants I. , Huyskens G. , Ebrahimi M. , Kime D. E. , Ollevier F.
Published: April 2005

The optimal ratio of spermatozoa : egg (15 000 : 1) for artificial insemination of African catfish Clarias gariepinus gave fertilization and hatching rates of 80 and 67%, respectively. Below a sperm : ova of 3000 : 1 fertilization success decreased significantly. Excessive sperm (>15 000 : 1) partly inhibited fertilization success. Sperm motility was decreased significantly by 0·001 mg 1−1 Hg2+ as HgCl2, but its effect on fertilization was dependent on the sperm : ova ratio, since excess sperm masked the effect of the pollutant. The most sensitive sperm : ova ratio for monitoring pollutant effects on fertilization success was 1500 : 1, which corresponds to half the minimal amount that yields a high fertilization rate in artificial insemination. There was a good correlation between fertilization and hatching rates (r=0·83; P<0·05). Although both fertilization and hatching rates provide equally good indicators of fertilization success, the more rapid fertilization rate test is recommended since it requires only 12 h.
An individual‐based model for predicting the emergence period of sea trout fry in a Lake District stream
Authors: Elliott J. M. , Hurley M. A.
Published: April 2005

The objective of this study was to predict interannual fluctuations in the emergence period of sea trout fry, using models developed from field data for 70 excavated redds, and laboratory data on egg and alevin development at 30 constant temperatures (range 1·5–10·5° C with 100 naturally fertilized eggs at each temperature). Egg weight and numbers per redd both increased with female length; a power function described the relationship. Early spawners were the largest females laying the largest and most numerous eggs, whilst late spawners were the smallest females laying the smallest and least numerous eggs; middle spawners being intermediate between these two extremes. Mean values for egg weight and numbers of eggs per redd were obtained for these three groups. Hatching and emergence times in the laboratory decreased with increasing temperature. Of five models tested for hatching time, the best fit was provided by a three‐parameter hyperbolic model which formed the asis of the individual‐based model used to predict egg hatching and fry emergence. Model development was described in detail and the final equations predicted the times taken for 5, 50 and 95% of the fry to emerge, and hence the period over which 90% of the fry emerged. Analogous models were obtained for egg hatching. All models were excellent fits to the laboratory data. Hatching times for eggs kept in perforated boxes in the stream were almost identical to those kept at similar mean temperatures in the laboratory. Model predictions of fry emergence times were validated by field data for 8 years (1967–1971, 1974, 1975, 1980). The chief objective was therefore fulfilled, and predictions for the 30‐year study (1967–1996) revealed a large variation in the timing of emergence (extremes: 11 March–4 April 1989, 15–20 May 1979). Most of the variation in median emergence date was due to variations in water temperature, with spawning dates as a secondary factor; the latter, however, had a greater effect on the length of the emergence period.
Accuracy and precision in eel age estimation, using otoliths of known and unknown age
Authors: Svedäng H. , Wickström H. , Reizenstein M. , Holmgren K. , Florenius P.
Published: April 2005

Using otoliths of eels Anguilla anguilla of known and unknown age from fresh, brackish and marine waters, the accuracy of age estimation was uncertain and deviations from the correct age were dependent on reader, locality and fish age.
A morphological study of cells isolated from the perfused gill of dab and Atlantic salmon
Authors: Lin S.‐H. , Davidson G. A. , Secombes C. J. , Ellis A. E.
Published: April 2005

Single cell suspensions were derived from the gills of dab Limanda limanda and Atlantic salmon Salmo salar which were free from blood cell contamination. Gills were perfused with heparinized saline before the cells were liberated from their resident position using a procedure employing chelating agents and collagenase digestion. Cells were characterized using light and electron microscopy as well as histochemical staining. The results indicate that the cell types resident in the gill tissue should be capable of expressing local immune competence. Small and large lymphocytes, macrophages, neutrophils, eosinophilic granule cells, goblet cells, chloride cells and cells of unusual morphology were identified especially the presence of goblet cells apparently within epithelial‐like cells.
A sexually dimorphic basal anal‐fin ray expansion in the weakly discharging electric fish Gnathonemus petersii
Authors: Pezzanite B. , Moller P.
Published: April 2005

Male Gnathonemus petersii (Mormyridae) exhibit two structural, sexually dimorphic characters: anal‐fin ray bone expansion and an indentation of the posterior ventral body wall (formerly described as anal‐fin indentation). Females lack this bone expansion, but may show a slight indentation. Morphometric data on both characters were obtained from radiographs of 414 fish (males and females) ranging in size from 60 to 276 mm Ls. Both body wall indentation and bone expansion began to develop in males of about 120 mm Ls. At 160–180 mm, the sex ratio of fish with expansion to fish without expansion was 50 : 50. Androgens seem to affect the expression of both these sexual dimorphisms. Bone expansion may provide increased bone surface for muscle attachment and thus facilitate the anal‐fin reflex during courtship behaviour.
Direct mate choice maintains diversity among sympatric cichlids in Lake Victoria
Authors: Seehausen O. , Witte F. , Van Alphen J. J. M. , Bouton N.
Published: April 2005

Mate choice may play an important role in animal speciation. The haplochromine cichlids of Lake Victoria are suitable to test this hypothesis. Diversity in ecology, coloration and anatomy evolved in these fish faster than postzygotic barriers to gene flow, and little is known about how this diversity is maintained. It was tested whether recognizable forms are selection‐maintained morphs or reproductively isolated species by investigating in the field reproductive timing, location of spawning sites, and mate choice behaviour. There was a large interspecific overlap in timing of breeding and location of spawning sites, which was largest in members of the same genus. Behavioural mate choice of such closely related taxa was highly assortative, such that it is likely that they are sexually isolated species and that direct mate choice is the major force that directs gene flow and maintains form diversity. The results differ from what is known about recent radiations of other lacustrine fish groups where speciation seems to be driven by diverging microhabitat preferences or diverging timing of reproduction, but are in agreement with predictions from models of speciation by diverging mate preferences.
The trophic role of lutjanid fish and impacts of their fisheries in two ecosystems in the Gulf of Mexico
Authors: Arreguín‐Sánchez F. , Manickchand‐Heileman S.
Published: April 2005

The trophic role of snappers was evaluated on the continental shelves of the south‐western Gulf of Mexico and the Yucatan in the south‐eastern Gulf of Mexico. Mass‐balanced, steady‐state trophic models of the two ecosystems were constructed with Ecopath and perturbations were simulated in the ecosystems with Ecosim by increasing fishing mortality. Impacts were measured by changes in biomass of snappers and other groups, and in some indices of stability: persistence, recovery time and resilience. The snapper populations differed between ecosystems. The western Gulf of Mexico system appeared more complex and more stable than the Continental Shelf of Yucatan. Although overall stability indices between ecosystem suggested a similar structure and function, there were clear differences at a group level. Correlation of stability attributes between groups suggested differences in the role of snappers between the ecosystems suggesting that each stock should be managed individually.
Impact of flood control schemes on river fish migrations and species assemblages in Bangladesh
Authors: Halls A. S. , Hoggarth D. D. , Debnath K.
Published: April 2005

A mark‐recapture programme at the Pabna Irrigation and Rural Development Project (PIRDP) site in NW Bangladesh showed that Catla catla, Channa striata and Wallago attu migrated through the sluice gates, both with and against prevailing currents in different season, while the smaller Anabas testudineus, Glossogobius giuris and Puntius sophore did not. Species assemblages were significantly different inside and outside the flood control, drainage and irrigation (FCDI) schemes, with up to 25 species absent or less abundant inside compared to outside. The majority of these species were large predators or conspicuous members of the highly prized migratory ‘whitefish’ category, including silurid catfish, Indian major carps, mullets and clupeids. In their absence, species inside FCDI schemes were dominated by much smaller resident ‘blackfish’ species. Assemblages inside FCDI schemes thus had both a reduced species richness, and a unit value reduced by up to 25%. It was concluded that FCDI schemes such as the PIRDP negatively affect fish species assemblages and stock values, by reducing the accessibility of impounded floodplains to migrant fish. Though some fish are capable of penetrating existing sluice gates, management measures are required to encourage the passage of more species.
Genetic population structure in the Lake Tanganyika sardineLimnothrissa miodon
Authors: Hauser L. , Carvalho G. R. , Pitcher T. J.
Published: April 2005

There was significant morphological differentiation among samples of Tanganyika sardineLimnothrissa miodon, indicating non‐random association of fish. Individuals within schools appeared to be unrelated as high mtDNA haplotype diversity demonstrated the presence of many maternal lineages in each school. Nevertheless, there was evidence from allozyme analysis for genetic differentiation on a very small geographical scale, possibly even among individual schools, without any clear geographical boundaries among populations. Similar microgeographical differentiation at the allozyme level was found in several marine pelagic species, suggesting a general pattern of random genetic structure in pelagic schooling fish. Such genetic patchiness may arise from biased reproductive success in localized spawning events and long‐term stability of schools, resulting in genetic differentiation among schools. While the present results are preliminary, the far‐reaching implications both for fisheries management and for evolutionary processes in pelagic species warrant further research on microgeographical genetic patterns using more sensitive markers.
Shelter selection in juvenile Atlantic salmon, or why do salmon seek shelter in winter?
Authors: Valdimarsson S. K. , Metcalfe N. B.
Published: April 2005

During winter, juvenile Atlantic salmon Salmo salar become nocturnal and seek refuge during the day in the stream bed gravel interstitial spaces. The function of this behaviour is unclear, but two major types of hypothesis have been proposed. One is that the fish are hiding from something (e.g. a predator) and the other is that the fish are seeking shelter from the water current. These hypotheses were tested by examining the selection of juvenile salmon for refuges that offered different degrees of concealment or shelter. The fish clearly preferred refuges that allowed them to hide (i.e. they were dark and opaque) but offered little shelter from the current. Therefore, it can be assumed that the primary function of this nocturnal behaviour during winter is most likely to hide from diurnal predators.
Functional morphology of gills and respiratory area of two active rheophilic fish species, Plagioscion squamosissimus and Prochilodus scrofa
Authors: Mazon A. de F. , Fernandes M.N. , Nolasco M.A. , Severi W.
Published: April 2005

Measurements of gill dimensions were carried out on two ecologically distinct active rheophilic teleost species, the curvina Plagioscion squamosissimus and the curimbatáProchilodus scrofa, and were analysed in relation to body mass according to the equation Y=aWb. The gill respiratory areas of P. squamosissimus and P. scrofa were large as expected for active fish and increased with increasing body mass (b=0.70 and 0.72, respectively) showing no significant difference between them. However, the large respiratory area of both species was realized in a different way revealing an adaptation to the plasticity of head components related to feeding habits. Consequently, significant differences were found between the number and average length of gill filaments and the bilateral area of secondary lamellae. The respiratory area of P. scrofa was due mainly to larger bilateral surface area of the secondary lamellae and its growth coefficient (b=0.51) that was significantly higher (P<0.05) than that found for P. squamosissimus (b= 0.36). The frequency of secondary lamellae mm−1 of filament was similar in both species (22 ± 2 on one side of gill filament). The dimensions of gill components and the respiratory area of these species suggest a complex interaction between head form, and feeding habits related to the functional morphology of the gills to meet the oxygen requirements of each species.
Responses of juvenile rainbow trout, under food limitation, to chronic low pH and elevated summer temperatures, alone and in combination
Authors: Dockray J. J. , Morgan I. J. , Reid S. D. , Wood C. M.
Published: April 2005

Rainbow trout were exposed (90 days) in synthetic soft water to sublethal low pH (5.2) and a simulated climate warming scenario (+2°C above the control summer temperature range of 16.5–21° C), alone and in combination, under conditions of limited food (∼4% dry body weight day−1). Weight specific oxygen consumption rates (Mo2) were ∼55% of Mo2(max), in contrast to ∼75% of Mo2(max) found in trout fed an unlimited ration. This is likely due to a reduction in food quantity and thus feeding activity. However, the trout exposed to low pH at control temperatures exhibited higher conversion efficiencies and increased growth. In contrast, trout exposed to +2°C had reduced growth rates. No ionoregulatory disturbance occurred in any treatment, suggesting that this ration was sufficient to provide a replacement salt load in the diet. Energy budgets indicated that the limited ration resulted in a lowered optimum temperature for growth, with a greater proportion of the energy intake dissipated for metabolic expenditure, resulting in reduced conversion efficiencies. A fourfold reduction in faecal and unaccounted energy losses indicated higher absorption efficiencies than in satiation‐fed trout.
Red blood cell adrenergic responses in Amazonian teleosts
Authors: Val A. L. , de Menezes G. C. , Wood C. M.
Published: April 2005

Erythrocytes from Amazonian teleosts of the Rio Negro were surveyed for the presence of adrenergically mediated Na+/H+ exchange. Washed red blood cells (RBCs) incubated in HEPES‐buffered Cortland saline were stimulated with 10−4 M L‐adrenaline. The adrenergic response was clearly present in two characids, the tambaqui Colossoma macropomom and the jaraqui Semaprochilodus insignis, as demonstrated by a decrease in the pHc‐pHi gradient across the RBC membrane, an uptake of Na+ from the extracellular medium, and RBC swelling. The latter was signalled by increased mean corpuscular volume (MCV) and decreased mean corpuscular haemoglobin concentration (MCHC). The response did not occur in two other characids, the black piranha Serrasalmus rhombeus and the aracu Leporinus fasciatus or in two silurid catfish, the piranambu Pinirampus pirinampu and the acari‐bodo, armoured catfish, Pterygoplichthys multiradiatus. In acari‐bodo, the Na+/H+ exchange response was similarly lacking under anoxic conditions. Oxygenated/deoxygenated comparisons revealed the presence of a marked Root effect in jaraqui and its absence in acari‐bodo. GTP dominated over ATP as the major intracellular phosphate in all six species. There were no significant changes in any nucleoside phosphate (ATP, ADP, AMP, GTP, GDP, or GMP) in response to adrenaline in any species.
Influence of weight upon in vitro protein digestion in rainbow trout
Authors: Bassompierre M. , Kristiansen H. R. , McLean E.
Published: April 2005

Protein digestive capacity, measured by an in vitro method, was examined in individual rainbow trout of four weight groups (40–875 g; n= 14 group−1), using three fish meals (FM). Differences (P <0.05) were found in digestive capacity between groups and with FM grade used. Larger fish expressed greatest catalytic capacity.