bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid data collection and assessment of the biology of Acanthurus nigrofuscus at Woleai Atoll, Micronesia
Authors: Dalzell P. , Smith A.
Published: April 2005

Traditional community fishing methods commonly employed in the tropical Pacific were used to generate information on the fishery biology of Acanthurus nigrofuscus at Woleai Atoll, Micronesia, over a short time period. A simple depletion model was used to estimate the biomass of A. nigrofuscus at four back reef lagoon sites at Woleai, using two different fishing methods; spear fishing and drive‐in‐net fishing. The mean biomass and density of A. nigrofuscus on the lagoon reefs was 8000 g ha −1 and 183 fish ha −1 respectively, with a total estimated standing stock for the lagoon of 91 500 fish or a biomass of 4·0 t. The size frequencies of fish caught by spear fishing were biased towards larger sized individuals, while those from drive‐in‐net fishing were thought to be more representative of the true population size frequencies. Variation in the density and biomass of A. nigrofuscus at the four reef sites was thought to be due to the length of time between episodes of community fishing at each reef site. The sex ratio (male: female) of A. nigrofuscus was significantly different from unity (1: 0·47) and males grew larger than females. Sexually mature fish were present in all size classes above the minimum capture length and spawning activity was greatest during the period of the full moon.
Do the habitats, mouth morphology and diets of the mullids Upeneichthys stotti and U. lineatus in coastal waters of south‐western Australia differ?
Authors: Platell M. E. , Potter C. , Clarke K. R.
Published: April 2005

Two benthic carnivorous goatfish (Mullidae), Upeneichthys stotti (max total length, LT= 179 mm) and U. lineatus (max LT= 257 mm), were trawled from the inner continental shelf waters of Western Australia. U. stotti was found almost exclusively offshore at 20–35 m depth, while U. lineatus was most abundant inshore at 5–15 m depth. Smaller individuals of both species ate small, thin‐shelled mysids, tanaids and amphipods, while larger fish ate large, hard‐bodied isopods, carid decapods and brachyuran crabs. Classification and ordination of the mean volumetric percentage contributions of the prey (dietary samples) of both species from all sites and in each season did not lead to a clear separation between these two species. However, ordination demonstrated that the dietary samples of the two species were distinct when the two species were found together, and when fish of sequential 20‐mm length intervals were used. The interspecific size‐class differences were consistent with the results obtained using Schoener's overlap index, for which values >0·6 were recorded for only two of the 45 possible interspecific pairwise comparisons. Since these interspecific differences occurred despite virtually identical mouth sizes and morphologies, the two species must feed in a slightly different manner and/or in different microhabitats. While most comparable‐sized fish ate tanaids and amphipods, U. stotti ate more relatively mobile epibenthic mysids, cumaceans and carid decapods, whereas U. lineatus ate more larger and slower‐moving burrowing bivalves, onuphid polychaetes and brachyuran crabs. The partial partitioning of habitats, when combined with differences in the diet, would help facilitate the co‐existence of these two mullids when they are abundant.
Survival, growth and sex ratios of gynogenetic diploid honmoroko
Authors: Fujioka Y.
Published: April 2005

Survival, growth and sex ratios of gynogenetic diploid honmoroko Gnathopogon caerulescens induced by blocking the release of the second polar body were examined. Mean survival of gynogenetic juveniles at 130 days after hatching was about 33% lower than that of the controls. No significant difference was seen in early growth between control and gynogenetic diploids. Standard length and body weight in six groups of gynogenetic progeny were significantly greater but in two groups were significantly smaller than in the controls. Although 69% of gynogenetic diploids had well‐developed gonads, the remaining 30% had undeveloped gonads (small in size or thread‐like), and those gonads were divided into four types. The mean proportion of females in the 10 gynogenetic groups was 87·2% which was significantly (P <0·01) higher than in the controls (44·7%). Gynogenetic diploids included 3·0–35·3% males. Most of those males produced a high proportion of female progeny, but the proportion of male offspring varied widely. From these results, the sex determining mechanism in honmoroko was presumed to be female homogamety, but other factors resulted in the production of males.
The effect of meal size on gastric evacuation in whiting
Authors: Andersen N. G.
Published: April 2005

Gastric evacuation experiments were performed on whiting Merlangius merlangus fed discrete meals of different sizes. Herring Clupea harengus, sandeel Ammodytes tobianus, common goby Pomatoschistus microps, and brown shrimp Crangon crangon were tested as prey. A simple power model to describe gastric evacuation was evaluated and compared with a power model expanded as a function of meal size. The model parameters were estimated by means of nonlinear least squares. When all meal sizes were included the estimates of the power (curvature) parameter in the expanded model were within the range 0·36–0·77 for the different prey. The power estimates in the simple model were generally close to 0·5. The exception was crustacean prey, which gave a higher value. In the simple model the power estimate represents a compromise between the curvatures of the curves fitted to the observations for each meal size and the relationship between meal size and overall evacuation rate. Compared with an expanded model a simple model with a power value of 0·5 gave a suitable description of the gastric evacuation of fish prey independent of meal size. The variation of data was proportional to meal size, and this could be taken into account in the estimation procedure by expressing stomach contents relative to meal size.
Scale morphology in Malawian cichlids
Authors: Kuusipalo L.
Published: April 2005

The morphology of 24 endemic cichlid species from Lake Malawi was studied with scanning electron microscopy. Several structures possibly of value for taxonomic and evolutionary studies were discovered. Six types of scale shapes and three types of interradial denticles were detected. The spiny area in the exposed part of the scale varied from nonexistent to 148° wide. Several regenerated scales with large focus and short radii were found. Various scale characters, which may prove valuable for phylogenetic purposes, are described and their use in phylogeny construction tested.
Genetic evidence for depth‐ and spatially separated stocks of the deep‐water spikey oreo in Australasian waters
Authors: Elliott N. G. , Lowry P. S. , Grewe P. M. , Innes B. H. , Yearsley G. K. , Ward R. D.
Published: April 2005

Samples of Neocyttus rhomboidalis from eight areas off southern Australia and eastern New Zealand were examined to assess the stock structure of the species. No spatial heterogeneity was detected for mitochondrial DNA variation after restriction analysis by two enzymes detecting polymorphic cut sites. Twenty mtDNA haplotypes were recorded, with an overall haplotype diversity of 0·683. Twenty‐eight allozyme loci were examined; the mean heterozygosity per locus was 13·0%. Significant sample heterogeneity was detected at three of twelve polymorphic loci: MPI*, PGM‐1* and, most strikingly (GST=0·43), sSOD*. Most of the sSOD* differentiation was associated with depth rather than geographical separation; sSOD* allele frequencies of shallow and deep samples being very different. It is suggested that the correlation between the sSOD* allele frequencies and depth is more likely to reflect natural selection than reproductive isolation. The spatial patterning of the MPI* and PGM‐1* data suggest there are at least three geographic stocks of N. rhomboidalis in Australasian waters: (1) New Zealand, (2) Western Australia and South Australia, (3) west Tasmania to New South Wales and Lord Howe Rise.
Chloride cell apical surface changes in gill epithelia of the armoured catfish Hypostomus plecostomus during exposure to distilled water
Authors: Fernandes M. N. , Perna S. A. , Moron S. E.
Published: April 2005

Armoured catfish Hypostomus plecostomus were exposed to distilled water for 15 days. High chloride cell proliferation occurred on the filament and lamellar gill epithelia. The apical surface of the chloride cells (66% of cells in both epithelia) showed significant reduction in the aquatic environment which was characterized by the development of a sponge‐like organization. The chloride cell response suggests that these features could create a microenvironment which may favour either the reduction of ion loss or ion uptake in a environment characterized by an absence of ions.
A preliminary investigation of allozyme genetic variation and population geographical structure in Aphanius fasciatus from Italian brackish‐water habitats
Authors: Maltagliati F.
Published: April 2005

A total of 150 individuals from Aphanius fasciatus from coastal brackish‐water habitats was analysed by allozyme electrophoresis to collect data on its genetic variation. From 22 enzymes, 43 putative enzyme‐coding loci were resolved, 12 of which were polymorphic at P0·99 level. Only one of the 31 probability tests showed a significant departure from the Hardy‐Weinberg equilibrium. Aphanius fasciatus showed low levels of genetic polymorphism, with expected heterozygosity values ranging from 0·027 (S.E.=0·013) to 0·064 (s.e.=0·023). Nei's genetic distances between populations ranged from 0·002 to 0·042. Weir & Cockerham F‐statistics showed high levels of genetic heterogeneity among populations (jackknifed θ=0·302, s.e.=0·045) and estimates of Nm were < 1, indicating restricted gene flow. Significant positive correlation between genetic distance and geographical distance matrices, detected by Mantel's test (g=1·941; P0·001), is consistent with the prediction that the species is genetically structured by isolation‐by‐distance.
Multivariate map representation of phylogenetic relationships: application to tilapiine fish
Authors: B‐Rao C. , Majumdar K. C.
Published: April 2005

Distance matrices obtained from allozyme studies on tilapiine fish are analysed by a multivarite approach. A hierarchical clustering procedure facilitated comparison with tree representations. A map‐like representation provided information additional to the tree representation. The current belief that Sarotherodon is closer to Oreochromis than to Tilapia is strengthened. But while it may be the link between these genera at the species level, it is not entirely distinct from Oreochromis at the molecular level. Further, Sarotherodon and Oreochromis species may have arisen from Tilapia in several speciation events. Some of the species interrelations agreed with inferences from morphological data, and disagreed with those from a consensus maximum parsimony (MP) tree. It is suggested that both Chromidotilapia guntheri and Tylochromis jentinki are ancestral to diVerent sub‐groups of Tilapia, so that inferences from morphological studies and the consensus MP method are both partially correct. The graphical representation also suggests that the Nile tilapia strains in Asia may be derived from Egypt rather than from Ghana. It is advantageous to use the map‐like and tree representations together for maximum visual informativeness and inference from the data.
Seasonal changes in the body composition of young riverine Atlantic salmon and brown trout
Authors: Berg O. K. , Bremset G.
Published: April 2005

The body composition of protein and fat in Atlantic salmon Salmo salar and brown trout Salmo trutta before and after winter was investigated in a temperate, small river, normally ice covered from the middle of November until the end of March. Fat, protein and specific energy declined greatly in winter but were replenished rapidly in spring. Rates of decline were slower for the smallest fish, which also had the lowest specific content of fat, protein, and energy, while the differences in absolute amounts were greatest for the largest fish. The mean specific fat content was reduced by 45–70% during winter, relative to the pre‐winter period (September). Mean daily reductions in specific enegy of the larger size groups of brown trout (3·7 × 10−3 kJ g−1 day−1) were almost half of the corresponding values for the largest Atlantic salmon (6·3 × 10−3 kJ g−1 day−1) during winter. A minor reduction in protein content was found during winter, with mean reductions of 6–10% in comparison to those in September. During spring the fat content was replenished rapidly, particularly for the smallest salmon fry (a threefold increase from April to June). Fat content in the larger salmon and trout increased by about 1·8 times. Based on estimated metabolic rates, digested energy during wintertime may contribute about two‐thirds of the brown trout fry's energy demand. For Atlantic salmon, the corresponding value is about 50%. The winter period put considerable stress on the young salmonids living in lotic environments, in particular for the smallest fry with the lowest energy content before winter and the largest losses during winter. This should make the fry more vulnerable to adverse abiotic and biotic factors.
Comparison of mitochondrial DNA sequences between the European and the Adriatic sturgeon
Authors: Ludwig A. , Kirschbaum F.
Published: April 2005

Intra‐ and interspecific diVerences in mitochondrial 12S ribosomal DNA sequences of Acipenser sturio and Acipenser naccarii were investigated. No variable sites were found in the sequences of nine A. sturio or in six A. naccarii. Seven substitutions were detected between A. sturio and A. naccarii.
Intersexual diVerences in aggression in juvenile rainbow trout
Authors: Johnsson J. I. , ÅKerman A.
Published: April 2005

Agonistic interactions were observed in dyadic contests between size‐matched rainbow trout. The results suggest that male juveniles are more aggressive than females.
Juveniles of non‐resident fish found in sheltered rocky subtidal areas
Authors: Henriques M. , Almada V. C.
Published: April 2005

Juvenile fishes of 22 species collected on a rocky shore area at Arrábida (Portugal) fell into three groups: (i) incidentals (four species); (ii) those in transit to a nearby estuary (three species); and (iii) nursery residents (15 species). For groups ii and iii this habitat seems to play an important role in their early life stages.
Stochastic simulation of size variation in turbot: possible causes analysed with an individual‐based model
Authors: Imsland A. K. , Nilsen T. , Folkvord A.
Published: April 2005

Causes of size variation in a population of juvenile turbot were studied using an individual based model (IBM). Each simulation started with 800 (divided into eight groups of 100 each) 120‐day‐old (posthatch) juveniles and was run for 140 days, and the data gained from model simulations compared directly with the result of a laboratory study with size‐graded turbot. Stochastic growth with memory, which was included in the models as an individual genetical growth rate variation, is important in explaining size variation, and the combination between individual genetic growth rate and social interactions related to size‐dependent hierarchies also contributes to size variation. The use of size‐dependent growth rate alone fails to explain size variation, and is of little value in predicting size variation in turbot culture. Further, the results indicate formation of different types of size hierarchies for different sizes of juvenile turbot.
Social status and growth rates as determinants of site attachment in juvenile Atlantic salmon
Authors: Huntingford F. A. , Braithwaite V. A. , Armstrong J. D. , Aird D. , Thorpe K. E. , Joiner P.
Published: April 2005

This paper describes an experimental study of the effects of food supply, growth rates and social interactions on homing by juvenile Atlantic salmonSalmo salarin response to displacement. Groups of five fish were housed in a section of an artificial stream and given either rations allowing maximum growth (the rich condition) or 0·1 of this amount (the poor condition); daily specific growth rates were significantly higher in the rich condition. After a 6‐day settlement period, the fish were captured, displaced downstream and their movements recorded over the next 3 h. Prior to displacement, the fish showed a high degree of site fidelity and high levels of aggression. Dominant fish and those with stronger site attachment grew faster prior to displacement, these effects being independent. Following displacement, 24% of all fish returned to their previously favoured site and stayed there, 23% returned home initially, but subsequently moved on, 5% settled in a new site and 49% failed to move. The distribution of responses was identical for the rich and poor conditions, but fish that homed were dominant and had grown faster during the pre‐displacement period.
Critical involvement of dietary docosahexaenoic acid in the ontogeny of schooling behaviour in the yellowtail
Authors: Masuda R. , Takeuchi T. , Tsukamoto K. , Ishizaki Y. , Kanematsu M. , Imaizum K.
Published: April 2005

To investigate involvement of the central nervous system in the ontogeny of behaviour, diets of differing quality were used to rear yellowtail Seriola quinqueradiata larvae and juveniles. Artemia nauplii enriched with oleic acid (OA), eicosapentaenoic acid (EPA), or two different concentration levels of docosahexaenoic acid (DHA) were fed to yellowtail larvae (LT 7 mm; 13 days old) for 12 days, and their behavioural development was analysed together with growth, survival, activity and fatty acid composition. Yellowtail fed with DHA–enriched Artemia showed mutual attraction behaviour at 11 mm LT, while those fed with OA– or EPA–enriched Artemia did not show this behaviour at the same size. While fish in the OA group showed poor growth, survival and activity index, fish in the EPA group were similar to the two DHA groups. In addition, most fish tested, including the OA group, showed clear optokinetic responses. Fatty acid composition of the diet was reflected in that of the fish body. Therefore, dietary DHA in the larval stage is considered to be essential for the development of schooling behaviour in the yellowtail.
Genetic variation and stock structure of school mackerel and spotted mackerel in northern Australian waters
Authors: Begg G. A. , Keenan C. P. , Sellin M. J.
Published: April 2005

The total mean sample heterozygosity calculated from eight polymorphic loci was 0·172 (0·047 S.E.) (Fst 0·025) for school mackerel Scomberomorus queenslandicus, and for spotted mackerel S. munroi was 0·110 (0·074 S.E.) (Fst 0·038). There was no evidence of temporal variation for either species as significant genetic differences were not detected between months or year classes within areas. Spatially, school mackerel have a complex stock structure, with stocks being associated with large embayments. In contrast, spotted mackerel appear to comprise a single stock in Australian east coast waters. Both species showed a significant pattern of stock structure between Australian east coast and northern (Arafura Sea) samples.
Feeding performance of Lake Victoria rock cichlids: testing predictions from morphology
Authors: Bouton N. , Van Os N. , Witte F.
Published: April 2005

Cichlid fishes that seem specialized phenotypically to exploit certain resources often act as generalists in the field. It is attempted to resolve this paradox by measuring feeding performance. There are two ways of feeding, namely suction feeding and biting, that set conflicitng demands on the anatomy. Rock‐dwelling cichlids of the genus Neochromis are specialized biters, feeding largely on filamentous algae and benthic organisms. Pundamilia nyererei is one of the most specialized suction feeders among rock cichlids, its diet being zooplankton and insect larvae. A morphological analysis showed that the three Neochromis species are better adapted anatomically to biting than P. nyererei, while P. nyererei is better adapted to suction feeding. Feeding performance was tested on algal substitute and Chaoborus larvae, representing filamentous algae and zooplankton, respectively. As expected the Neochromis species fed most efficiently on algal substitute, N. rufocaudalis and N. omnicaeruleus taking per bite 2.6 times as much as P. nyererei, and N. greenwoodi 1.7 times. Unexpectedly, the species examined were all well able to collect Chaoborus. P. nyererei collected only 1.2 times as many larvae per suction act as the Neochromis species. Analysis of the stomach contents showed that P. nyererei punctured, or lacerated, the larvae with the pharyngeal jaws, while the Neochromis species swallowed them mostly intact. Thus, feeding on Chaoborus, P. nyererei may be optimizing energy gain and not intake rate.
Energy flow and network analysis of Terminos Lagoon, SW Gulf of Mexico
Authors: Manickchand‐Heileman S. , Arreguín‐Sánchez F. , Lara‐Domínguez A. , Soto L. A.
Published: April 2005

The food web in Terminos Lagoon, south‐western Gulf of Mexico was dominated by the detrital pathway, with benthic invertebrates playing a significant role in transferring energy from detritus to higher trophic levels. The fish yield per unit of net primary production was only 0.04%. Fractional trophic levels ranged from 1.0 to 3.31, with fish occupying the highest trophic levels. Using network analysis, the system network was mapped into a linear food chain and five discrete trophic levels were found with a mean trophic transfer efficiency of 7%. Analysis of mixed trophic impacts showed that fish had very little impact on the other compartments, due to their relatively low biomass and consumption, with exception of the Engraulidae. Detritus and lower trophic levels had significant positive impacts on other groups in the system, suggesting ‘bottom‐up’ control of the food web. A high detritivory: herbivory ratio (4.6: 1) indicated that most of the primary production was recycled through the detritus‐based food web. A Finn cycling index of 7% and average path length of 10 were obtained.
The relationship between reef fish community structure and environmental variables in the southern Mexican Caribbean
Authors: Lara E. Núñez , González E. Arias
Published: April 2005

The reef fish community of the Mexican Caribbean and the factors governing its structure are poorly known. Using canonical correspondence analysis (CCA), the relationship between fish community species composition and abundance, and environmental variables was investigated at three Mexican Caribbean reefs. These reefs are separated by c. 70 km: Boca Paila, located in the northern Sian Ka'an Biosphere Reserve; Tampalam, in the southern portion of said reserve; and Majahual, an unprotected area near the Mexico/Belize border. One hundred and thirty‐four fish species belonging to 41 families were identified by underwater visual census. Their quantitative data, and 15 environmental variables collected during 60 sample transects, were analysed. The sample stations were distributed among the three reefs, and covered five dominant habitat types: reef lagoon, back reef, reef crest, reef front and reef slope. The variables estimated were: temperature, depth, current direction, current intensity, vertical relief, visibility, topographical complexity and substratum coverage (percent of sand, seagrass, algae, rock and rubbles, gorgonians, massive coral, branching coral and encrusting coral). Ordination diagrams with points based on fish species, sample sites, and environmental variables, showed a pattern mainly determined by degree of reef site complexity. Habitat scale environmental factors defined element distribution in three main areas: (a) reef fish species associated with lagoon and back reef sites of low topographical complexity; (b) species associated with intermediate complexity reef crest sites; and (c) species associated with high complexity reef front and reef slope sites. Nearly 52% of the variation in fish species data was explained by environmental variables in the direct and simultaneous ordination analysis. Topographical complexity was the most important variable, but depth, encrusting coral coverage, and vertical relief also had significant effect on fish species. Use of multivariate statistical methods proved valuable in deciphering the reef fish community structure patterns in the southern Mexican Caribbean. The current study provides a base for future reef fish research and regional tourism and fisheries management.
Seasonal grazing rates and food processing by tropical herbivorous fishes
Authors: Ferreira D. E. L. , Peret A. C. , Coutinho R.
Published: April 2005

Seasonal variability in grazing rates and food‐processing characters were assessed for three abundant fishes in a tropical rocky shore: the damselfishStegastes fuscus, the parrotfishSparisoma atomarium, and the surgeonfishAcanthurus bahianus. Significant differences were found in grazing rates among hour of day and seasons, and in food‐processing characters among seasons for the three fishes. Grazing rates forS. atomariumandA. bahianuspeaked at 1300 and 1400 hours forS. fuscus. Three main periods of different intensity in bite rates, low, intermediate and intense, were identified for all fishes. As expected, total bite rates, ingestion rates and gut fullness were highest inA. bahianus, the largest species studied, followed byS. atomariumandS. fuscus. S. atomariumwith fused jaw teeth, holds the highest bite size andS. fuscusthe lowest one. Gut turnover was high forS. fuscusand similar forS. atomariumandA. bahianus. Grazing rates and food‐processing characters seem to vary between seasons not only due to changes in temperature, but also affected by other factors. Fishes employ different food‐processing mechanisms and bear some differences in food‐processing characters to achieve optimal energetic supplies from a poor nutrient food resource.
Transport of larval fish in the Amazon
Authors: Araujo‐Lima C. A. R. M. , Oliveira E. C.
Published: April 2005

In the Amazon near Manaus, larvae of Characiformes, Clupeiformes, Tetraodontiformes, Pleuronectiformes, Gymnotiformes, Belonidae and Sciaenidae were sampled in the river during most of the year, except in June and July, when the water level was at its maximum. Characiformes, Tetraodontiformes and Siluriformes were found in the ichthyoplankton mostly during the rising waters, but Clupeiformes and Sciaenidae drifted in the river almost all year around. Egg abundance was extremely low, suggesting that they do not drift or have a very short residence time. Two types of larval drift seemed to occur: a rising water drift and a lowering water drift. Characiformes, Tetraodontiformes and some Clupeiformes drifted mostly during the rising waters and were more abundant near the banks. Their strategy seemed to be a passive dispersion towards the floodplain with the flood pulse. The high densities near the banks optimized their chances of reaching a floodplain inlet. The groups that drifted during the lowering waters showed an alternative strategy. They were flushed from the floodplain lakes and may have stayed in the main river channel for a few months before returning to the floodplain. Predation in the lakes during the period when water level decline was probably the force behind this drift.
Introgressive hybridization of tilapias in Zimbabwe
Authors: Gregg R. E. , Howard J. H. , Snhonhiwa F.
Published: April 2005

Three species of tilapia native to Zimbabwe, Oreochromis mossambicus, O. mortimeri and O. macrochir are not naturally sympatric, but because of transplantation they have been brought into sympatry. Allozymes of fish examined from Lakes Kariba, Kyle and Chivero showed evidence of introgressive hybridization. The data showed non‐random mating populations in Lakes Kariba and Kyle. All three reservoirs displayed individuals with intermediate principal component scores and hybrid index scores indicating hybridization.
Development of osteological structures in the sea bream: vertebral column and caudal fin complex
Authors: Faustino M. , Power D. M.
Published: April 2005

The development of cartilaginous structures in cultured sea bream Sparus aurata larvae and the timing of their ossification was studied. In cultivated sea bream larvae the first cartilaginous structure to be identified was hypural 1 at 4.1 mm notochord length (LN). By 5.3 mm LN, prior to the onset of ossification, it was possible to distinguish the following cartilaginous structures: all 23 neural arches, all 13 haemal arches and two of the four pairs of parapophyses. The neural arches 1–4 and 15–23 were formed on the notochord and elongated dorsally, while neural arches 5–14 appeared on the dorsal side of the spinal cord and elongated ventrally. Initiation of ossification occurred at 5.7–6.0 mm standard length (LS) when the cartilaginous ontogeny of the vertebral column was completed. Ossification was coincident with dorsal flexion at the posterior end of the notochord and occurred in a sequential manner: (1) dorsoanteriorly, the cartilaginous neural arches and the centra were the first structures to ossify; (2) ventrad at the centre, at 7.0–7.5 mm LS; (3) posteriorly at 7.1 mm LS the hypural complex and urostyle (24th centrum) were ossified; and (4) dorsad at the centre (neural arches and spines).
Inhibition of spawning and associated suppression of sex steroid levels during confinement in the substrate‐spawning Tilapia zillii
Authors: Coward K. , Bromage N. R. , Little D. C.
Published: April 2005

Substrate‐spawning Tilapia zillii failed to spawn in crowded holding tanks but exhibited a marked tendency to spawn soon after transfer to individually partitioned aquaria. Confined conditions suppressed the levels of serum 17β‐oestradiol (E2) and testosterone (T) in females, which remained low throughout the period of confinement. Levels of both steroids rose significantly following transfer of fish to individual aquaria and were maintained at consistently higher levels than those of fish which remained confined. Proportions of stage 3 (late perinucleolar) oocytes were significantly lower (P<0.001) in individual fish 21–30 days after transfer, coincident with significantly higher (P<0.01) proportions of stage 6 or 7 oocytes (late vitellogenic or maturing oocytes). However, no significant differences (P≥0.05) were detected between individual or confined groups of fish in the relative proportions of stage 2 (early perinucleolar), stage 4 (cortical alveolar) or stage 5 (early vitellogenic) oocytes. Atresia increased as the period of confinement increased. Following return of individual fish to confined conditions, blood steroids fell rapidly to levels seen in fish that had remained confined throughout. It is suggested that the reduced sex steroid levels detected during confinement were insufficient to allow developing oocytes to complete oocyte growth and maturation. The detection of significantly lower proportions of stage 3 and significantly higher proportions of stage 6/7 oocytes soon after transfer suggest that fish were preparing one batch of oocytes for spawning (stage 6/7 oocytes) whilst recruiting from a pool of previtellogenic oocytes (stage 3) for the ensuing spawning cycle.
Early development of the cephalic skeleton in the turbot
Authors: Wagemans F. , Focant B. , Vandewalle P.
Published: April 2005

At hatching Scophthalmus maximus shows no cartilaginous and no bony structure. Meckeľs cartilages appear when the fry are 1 day old, followed on day 2, by formation of the trabecular bars, fused at the outset to form a trabecula communis. Concurrently, the palatoquadrates complete the mandibular arch, and the first two pairs of ceratobranchials, associated with a pair of hyoid bars, form the beginnings of the hyobranchial system. By day 3, the parachordals have fused with the trabecular bars, the hyosymplectics have linked to the hyoid bars by interhyals, and the first four pairs of ceratobranchials have appeared. The first bony structures appear: the preoperculars. On day 8, the frontals develop above the orbits and the maxillaries and dentaries appear. On day 10, the primordia of the taeniae marginales appear, the palatoquadrates bear a pterygoid process, and to the branchial basket have been added the fifth pair of ceratobranchials and the four pairs of epibranchials. On day 12, both pairs of posterior pharyngobranchials are present. The premaxillaries develop in front of the maxillaires, and retroarticulars and the angulars complete the lower jaws. On day 13, a thin parasphenoid contributes to the floor of the neurocranium, and ectopterygoids and entopterygoids to the splanchnocranium. The set of opercular bones is complete. On day 15, the tectum synoticum closes the braincase posteriorly. The splanchnocranium possesses a basihyal and the pharyngobranchials of the first epibranchials. On day 18, the tectum posterius completes the dome of the braincase. The rear end and lateral walls of the skull are formed by the basioccipital, the exoccipitals, the pterotics, and the parietals. The suspensorium is nearly complete. From day 10, the first resorptions begin in parallel with the construction of the chondrocranium. Meckeľs cartilages each split in two, then the posterior part of the trabecular bars disappears. On day 23, the right taenia marginalis separates from the lamina orbitonasalis and curves towards the centre. Simultaneously, the right eye begins its migration to the left. This is the only metamorphosis‐linked asymmetry to appear during the development of the chondrocranium. On day 25, many more bony structures appear, a characteristic of this stage: the nasals, lateral ethmoids, mesethmoid, sphenotics, prootics, pleurosphenoids, epiotics, and supraoccipital. From this stage on, the bony structures continue to develop, while the front of the neurocranium and the jaws undergo a deep remodelling due to metamorphosis. The left taenia marginalis does not appear reduced until day 29. By day 45, there remain only a few small elements of the cartilaginous skull.
Predator avoidance in mummichog larvae from a polluted habitat
Authors: Zhou T. , Weis J. S.
Published: April 2005

Previous work has shown that adult mummichogs (Fundulus heteroclitus) from a polluted site (Piles Creek, PC, New Jersey) were more vulnerable to predation by blue crabs than fish from a more pristine site (Tuckerton, TK, New Jersey). The present study was conducted to compare the spontaneous activity, swimming performance and predator avoidance of fish of the two populations at early life stages. When raised in synthetic salt water, both newly hatched and 1–month‐old mummichog larvae from TK had greater spontaneous activity, swimming performance, and stamina than those from PC. In comparison to TK, PC larvae were less vulnerable to predation by yearling mummichogs at 1 week old, but were more vulnerable at 1 month old. Variation in behaviour and swimming ability of TK and PC larvae accounted for the differences in vulnerability to predation. TK larvae employed greater swimming and irregular movement, which was more successful for survival of older larger larvae. In contrast, PC larvae hid, often remaining motionless, which was advantageous for survival of young smaller larvae. Contaminants had been assumed responsible for the behavioural differences in the PC population. However, since differences were seen in larvae raised in synthetic salt water, it is possible that maternally transferred neurotoxicants (possibly delayed effects) and/or inherent factors also play a role.
Effects of constant short and long photoperiod regimes on the spawning performance and sex steroid levels of female and male sea bass
Authors: Prat F. , Zanuy S. , Bromage N. , Carrillo M.
Published: April 2005

Under constant short photoperiod, the spawning time of 2‐year‐old sea bass Dicentrarchus labrax was advanced as compared to controls, whereas spawnings were delayed under constant long photoperiod. High plasma levels of 17β‐oestradiol (E2/) and testosterone (T) in females were coincident with the appearance of vitellogenic oocytes in the ovary, while high levels of 11‐ketotestosterone (11‐KT) and T in males were coincident with the presence of spermiating males. Although plasma levels of E2 in females and 11‐KT in males were low during the remainder of the cycle, levels of T were always >1 ng ml−1 in both sexes, suggesting that T could play an important role during the initial stages of gonadal development. The profiles of E2 and T in females and 11‐KT and T in males exposed to constant short days were similar to those in the control group, but fish which were maintained under constant long photoperiods showed a bimodal pattern of these steroids. The results obtained from fish exposed to constant photoperiod regimes provide further evidence that an endogenous process could be operating to control the reproduction of sea bass.
Aspects of the biology of Nezumia aequalis from the continental slope west of the British Isles
Authors: Coggan R. A. , Gordon J. D. M. , Merrett N. R.
Published: April 2005

Nezumia aequalis is one of the most abundant fishes on the upper and middle continental slopes (500–1750 m depth zones) of the North‐east Atlantic with a peak abundance of three to four individuals 1000 m−2 swept area in the 750‐m zone. Mean and modal size increased with depth, fish from the Rockall Trough (RT) being larger than those at equivalent depths in the Porcupine Seabight (PSB). Sex ratios were close to parity in all depth zones. Females grew larger than males. Head length to total length and to total weight did not differ significantly between sexes but RT fish were heavier at any given length than PSB fish. Serial batch spawning occurred over the first three quarters of the year. Ovaries contained five size groups of eggs, the three largest groups being vitelline and contributing 27% of the absolute individual fecundity which was positively correlated with body size and ranged from 9109 to 26 847. Age determined from sagittal otoliths ranged from 1 to 10 years, the ageing method being validated by a time‐series study of the growing edge of otoliths. The von Bertalanffy growth parameter (k) was estimated at 0·175 and 0·216 from head length and otolith length, respectively.
Plasma cortisol and 17β‐oestradiol levels in roach exposed to acute and chronic stress
Authors: Pottinger T. G. , Yeomans W. E. , Carrick T. R.
Published: April 2005

Plasma cortisol levels were measured as an indicator of physiological stress in roach subjected to brief handling, or to a 14‐day period of confinement, and in undisturbed control fish, during winter (water temperature 5° C) and summer (16° C), at which time plasma 17 β‐oestradiol levels were also determined. Cortisol levels in undisturbed roach were low (mean 8·1 ng ml−1 at 5° C; 1·4 ng ml−1 at 16° C) and both handling and handling+confinement elevated blood cortisol levels significantly to 400 and 140 ng ml−1, respectively (at 5° C) and 700 and 600 ng ml−1, respectively (at 16) C). Blood cortisol levels had almost returned to baseline within 4 h following handling alone but in fish subjected to handling and prolonged confinement cortisol levels remained elevated for up to 168 h. Differences in baseline and poststress levels of cortisol, and in the rate of recovery from acute stress, were observed at the two different temperatures and the possible factors underlying these differences are discussed. Circulating levels of 17 β‐oestradiol were reduced significantly within 24 h of exposure to either acute handling or chronic confinement indicating that the reproductive endocrine system in roach is sensitive to disruption by stressors.
Phylogenetic relationships of Ponto‐Caspian gobies and their relationship to the Atlantic—Mediterranean Gobiinae
Authors: Simonovic P. D.
Published: April 2005

A phylogenetic analysis for five Ponto‐Caspian goby species belonging to the two genera Neogobius and Proterorhinus assigned to the sub‐family Gobionellinae was conducted, with five Atlantic—Mediterranean species of sub‐family Gobiinae, genera Gobius and Zosterisessor, as outgroup taxa. One hundred and two characters (37 continuous cranial osteological, 50 continuous external morphological, five discrete external morphological, four karyological, two vertebral and four external discrete qualitative characters) were studied. Parsimony analysis revealed that the two zoogeographically distinct groups of goby species comprise distinct phyletic lineages that are sister groups. The relation of neogobiids to the sub‐family Gobiinae was reconsidered, due to the sharing of the same state for the diagnostic character. The recently proposed classification for the genera Proterorhinus and Zosterisessor was rejected. The status of several of the lower ranked taxa was also considered [e.g. Gobius bucchichi as a member of the genus Zosterisessor and the sub‐generic status of Neogobius (Neogobius) fluviatilis and Neogobius (Apollonia) melanostomus]. The paleohistorical data suggest that those lineages, which may both descend from pre‐Oligocene Indo‐Pacific ancestors, separated at least 12 million years ago, during the early Miocene, after the formation of the Paratethys Sea, and then evolved independently. The Tethyan gobiine species evolved in the marine environment of the Mediterranean Sea and the Atlantic Ocean. The Ponto‐Caspian (i.e. Paratethyan) gobies of the genera Neogobiusa and Proterorhinus diverged in the late Miocene or early Pliocene. They probably evolved in the freshwater refuge in the Daccian Basin of the Paratethys Sea (the recent Black Sea basin).
The interaction of temperature and fish size on growth of juvenile halibut
Authors: Jonassen T. M. , Imsland A. K. , Stefansson S. O.
Published: April 2005

Growth rate of individually tagged juvenile halibut was influenced significantly by the interaction of temperature and fish size. The results suggest an optimum temperature for growth of juvenile halibut in the size range 5–70 g between 12 and 15° C. Overall growth rate was highest at 13° C (1·62% day −1). At c. 5 g at the beginning of the experiment, fish at 16° C had the highest growth rate (3·2% day −1), but reduced this rate as they grew bigger. At 9 and 11°p C, growth rates were equal or only slightly lower during the later stages of the experiment, while the fish at 6° C showed significantly lower overall growth rate (0·87% day−1). Optimal temperature for growth decreased rapidly with increasing size, indicating an ontogenetic reduction in optimum temperature for growth. Moreover, a more flattened parabolic regression curve between growth and temperature as size increased indicated reduced temperature dependence with size. Although individual growth rates varied significantly at all times within the experimental temperatures, significant size rank correlations were maintained during the experiment. This indicated an early establishment of a stable size hierarchy within the fish groups. Haematocrit was highest at the highest temperature while Na+/K+‐ATPase activity was inversely related to temperature. There was no difference in plasma Na+, Cl− and K+ concentrations among the temperature groups.
Evidence of differences in growth and food intake regulation in different genetic strains of channel catfish
Authors: Silverstein J. T. , Wolters W. R. , Holland M.
Published: April 2005

Norris and USDA‐103 strains of channel catfish Ictalurus punctatus were compared for growth rate and food conversion ratio under satiation feeding and restricted feeding (1% body weight day−1) regimes. At the start of the experiment Norris fish weighed 2·8 g, USDA‐103 fish weighed 14·0 g. Therefore, a regression of the loge of specific growth rate against the loge of mean body size with an empirically derived fixed slope of ‐0·37 was used to compare growth rates. Under both feeding regimes the USDA‐103 strain had faster specific growth rates and more efficient food conversion. In subsequent studies, voluntary food intake of size matched fish (60 g average) from these two strains was compared using a radiographic method. Fish were acclimatized to tank conditions for 3 weeks prior to voluntary food intake measurement. Half of the groups were deprived of food for 2 days prior to food intake measurement, while the remaining groups were fed 1% body weight day−1. The USDA‐103 strain fish ate significantly more food and grew faster than the Norris strain fish. Previously fasted Norris fish subsequently ate more than their fed counterparts, whereas the fed USDA‐103 fish consumed more food than the fasted USDA‐103 group. When the USDA‐103 strain fish were deprived of food for 4, 2 or 0 days, all groups subsequently consumed between 4·5 and 5·0% of body weight in one meal. The USDA‐103 fish, unlike the Norris fish were not stimulated to consume more after short‐duration fasting. Taken together, these results suggest that there are genetic differences in growth, food conversion ratio and regulation of food intake between Norris and USDA‐103 strains.
Movements of Hoplias aimara during the filling phase of the Petit‐Saut dam, French Guyana
Authors: De Morais L. Tito , Raffray J.
Published: April 2005

Twenty Hoplias aimara were tagged intraperitoneally with radio‐transmitters in the Sinnamary River, French Guyana. In November 1993, 13 tagged fish were released in an area which would be flooded by the Petit‐Saut reservoir impoundment in mid‐1994. Seven other tagged fish were released in January 1994, 20 km upstream of the upper limit of the reservoir. Hoplias aimara showed site fidelity: 75% of fish returned to their capture site before the test area was inundated. The remaining fish stayed close to the release area. Monitoring during three 24‐h cycles before reservoir filling showed that H. aimara has a limited home range, which is less marked in unconstrained reaches during the wet season (April to August) than in constrained reaches during the dry season (September to November). In natural conditions, H. aimara has a wider home range in unconstrained river reaches than in constrained river reaches. After closure of the dam, in September and October 1994 (dry season, low water) more than half of the total H. aimara tagged in the flooded zone migrated upstream following the rise of water.
Plasma levels of C18‐, C19‐ and C21‐steroids in captive and feral female sea bass
Authors: Rocha M. J. , Reis‐Henriques M. A.
Published: April 2005

Morphometric analysis of the gonads of sea bass Dicentrarchus labrax revealed that captive fish matured 1 month later than feral fish, but levels of gonadal steroids were identical in both groups at the same stage of sexual development. 17β‐oestradiol (E2) (up to 3 ng ml‐1) and testosterone (T) (up to 4 ng ml‐1) were highest during the gametogenetic period while 17,20β,21‐trihydroxy‐4‐pregnen‐3‐one (17,20β,21‐P) (free and sulphated) were maximal during the spawning period. Free 17,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐P) was very low and did not change (c. 0·5 ng ml−1) while 17,20β‐P‐sulphate increased during the spawning period in both groups (up to 2 ng ml−1). In contrast cortisol levels were higher in captive fish and increased during the spawning period (up to 100 ng ml−1). These results suggest that captivity delays vitellogenesis and spawning in sea bass without affecting the final levels of the gonadal steroids and further indicates a role for cortisol in the latter period. The increased levels during the spawning period suggests a pheromonal role for 17,20β‐P‐sulphate and 17,20β,21‐P‐conjugates and the involvement of 17,20β,21‐P in final ooccyte maturation.