Nested patterns of spatial diversity revealed for fish assemblages in a west European river

Abstract –  The longitudinal distribution of fish assemblages across a large west European river basin, the Garonne river (south-west France) were investigated using a self-organising map. This nonlinear statistical method was employed to classify sampling sites according to their species composition. We found three main nested patterns in an aggregated hierarchy: a replacement and succession of species along a gradient without defined boundaries, four main zones of fish assemblages and an upstream-downstream shift of fish communities. We suggest that fish assemblages are too complex to be identified with a single species as in the zonation model, and that the diversity patterns found might be part of the same ecological process influencing fish assemblages on different spatial scales. Thus, discrepancies in the analysis of longitudinal patterns of fish communities in streams may have been basically a matter of local conditions and of conceptual perception.     

Effects of gonadotropin-releasing hormone agonist and testosterone on gonadotropin subunit gene expression in female red seabream (Pagrus major)

We examined the effects of gonadotropin-releasing hormone agonist (GnRHa) and testosterone (T) on the level of gonadotropin subunit mRNAs in the pituitary of ovariectomized or intact female red seabream. Ovariectomy induced increase of seabream (sb) GnRH, glycoprotein (GP) α and luteinizing hormone (LH) β mRNA levels. GnRHa treatment also stimulated GPα and LHβ mRNA levels. T treatment reduced GPα and LHβ mRNA expression probably via negative feedback action on sbGnRH. Both GnRHa and T treatment had no effect on follicle-stimulating hormone (FSH) β mRNA levels. These results suggest that the regulatory mechanisms of GPα and LHβ gene expression differ from those of FSHβ gene.     

Effect of high water temperature on brain-pituitary-gonad axis of the red seabream during its spawning season

In the present study, we examined the effect of high water temperature on brain-pituitary-gonad (B-P-G) axis of a perciform fish red seabream, Pagrus (Chrysophrys) major during its spawning season (April-May). High water temperature negatively affected all levels in B-P-G axis and turned out to be the termination factor of the spawning season of this species.     

A strain-specific and a sex-associated STS marker for Asian arowana (Scleropages formosus, Osteoglossidae)

A sex‐associated amplified fragment length polymorphism and a strain‐specific random amplified polymorphic DNA marker were identified from Asian arowana (dragonfish; Scleropages formosus Müller & Schlegel) by screening pooled genomic DNA samples from three different strains as well as males and females respectively. Both markers were cloned, sequenced and successfully converted into sequence‐tagged‐site (STS) markers. The strain‐specific STS marker could be applied to differentiate the Indonesian golden strain of Asian arowana from the green and blood‐red strains before the stage when colours become identifiable. Individuals from the green strain could be sexed with an efficiency of 82.7% using the sex‐associated STS marker. Thus, populations with preferred sex ratios can be formed without the need of rearing a large number of fish.     

Larviculture of the Greasy Grouper Epinephelus tauvina F. and the Brown-Marbled Grouper E. fuscoguttatus F. in Singapore

This paper reports the larviculture of two grouper species, the greasy grouper Epinephelus tauvina and the brown-marbled grouper E. fuscoguttatus , and examines the technical feasibility of breeding the fish. Fertilized eggs for larviculture were obtained by induced spawning through multiple hormonal injections of the female brooders, followed by artificial fertilization for the greasy grouper and by natural spawning in netcages for the brown-marbled grouper.
For both species, larviculture was divided into three operational stages, i.e., stage 1 (day 0–12), stage 2 (from day 12 to day 24 for the greasy grouper and to day 30 for the brown-marbled grouper) and stage 3 (day 24 or 30 to metamorphosis). Larvae were transferred to clean tanks after each stage. Total mortality around day 5–8 was common for the greasy grouper. Several modifications, including the feeding with super-small strain rotifers, intensive feeding of rotifers with Nannochloropsis and the use of an oil-skimmer, have been made to improve the situation. Two other major problems in larviculture were the high mortality observed after day 25 in the greasy grouper and the high cannibalism from day 35 onwards for the greasy grouper and from day 30 onwards for the brown-marbled grouper. The shock syndrome exhibited by both species during the periods made culling of the fish impossible.
Based on the spawning and larval characteristics, brown-marbled grouper is considered a better potential species for large scale fry production than the greasy grouper.     

Can the mudskipper,Periophthalmus chrysospilos,tolerate acute environmental hypoxic exposure?

The mudskipper P. chrysospilos became inert at 0.76 μl O₂.ml⁻¹ when it was allowed to respire in a ‘closed respiratory chamber’. No ethanol was detected although it excreted three times more total carbon dioxide into the surrounding sea water than the amount of oxygen consumed. However, P. chrysospilos could survive environmental hypoxic exposure (0.8 μl O₂.ml⁻¹) for at least 6 h. Upon normoxic recovery, the oxygen debt repayment was only a small fraction of the oxygen deficit incurred during the 6 h of hypoxic exposure. It would therefore appear that P. chrysospilos was able to cope with environmental hypoxia by suppressing its metabolic rate.     

Genetic variation in different varieties of Siamese fighting fish using isoelectric focusing of sarcoplasmic proteins

Sarcoplasmic proteins of four colour varieties of Siamese fighting fish, Betta splendens Regan, were analysed by isoelectric focusing (IEF). Genetic polymorphisms were detected in six loci having isoelectric points: 4.92-5.00 (Sp-1), 5.33-5.48 (Sp-2), 5.90 (Sp-3), 6.31-6.35 (Sp-4), 6.58-6.70 (Sp-5) and 6.90 (Sp-6). For the Sp-1, Sp-2, Sp-4 and Sp-5 loci, there were two co-dominant alleles. At Sp-3 and Sp-6, one allele was dominant and the other null. Individuals within each locus were classified into phenotypes A, AB and B. Only homozygotes were found at Sp-2. Allele frequencies were calculated for each locus and tested for accordance with the Hardy-Weinberg equilibrium. Observed values for each phenotype at Sp-1, Sp-3, Sp-4, Sp-5 and Sp-6 agreed well with the expected ones. At Sp-2, genotypic frequencies for each variety deviated markedly (p < 0.01) from the equilibrium. When tested for homogeneity, no significant differences (p 0.95) in gene frequencies were found among the varieties except at Sp-2. Band sharing index (BSI), computed using the BIO-GENE v5.04 program, revealed high intravariety genetic similarities (0.701-0.740) and slightly above-average intervariety values (0.550-0.583). In this study, we estimated the levels of genetic variability in B. splendens, and proposed a genetic model for each polymorphic locus.     

Effects of salinity, dietary level of protein and 17α-methyltestosterone on growth hormone (GH) and prolactin (tPRL177 and tPRL188) levels in the tilapia, Oreochromis mossambicus

In the present study, we examined the long-term effects of environmental salinity, diet (35% and 25% crude protein) and 17-methyltestosterone (MT) on corresponding levels of pituitary and serum growth hormone (GH) and prolactins (tPRL₁₇₇ and tPRL₁₈₈) in the tilapia (Oreochromis mossambicus). We observed no discernible patterns in serum GH that would suggest an effect of salinity, diet or MT. However, serum GH levels in all treatments declined at 1 and 3h after first feeding. Serum tPRL₁₇₇ and tPRL₁₈₈ were significantly higher in freshwater (FW) than in seawater (SW) and levels were significantly affected by dietary protein. tPRL₁₇₇ levels were higher in all groups fed a 35% protein diet, but tPRL₁₈₈ levels were higher only in the groups fed the MT-treated 35% protein diet; only serum tPRL₁₈₈ levels were affected by MT. Moreover, serum tPRL₁₇₇ and tPRL₁₈₈ increased throughout the sampling time-course. Subsequent work using fasted tilapia suggests that first feeding is likely to initiate the post-prandial suppression of serum GH levels. In contrast with the picture observed in blood, pituitary glands of SW animals showed higher levels of GH than FW fish. Pituitary GH was elevated by MT in both FW and SW. We also observed that pituitary tPRL₁₇₇ and tPRL₁₈₈ levels were higher in FW fish than in SW fish; tPRL₁₇₇ and tPRL₁₈₈ levels were elevated by MT only in FW animals. To assess the somatomedin activity of plasma from FW- and SW-reared tilapia, we measured [35S]-sulfate incorporation into ceratobranchial cartilage explants in vitro. Plasma from SW-adapted tilapia showed greater activity in this assay than plasma from FW-reared tilapia, suggesting that the GH-dependent IGF bioactivity of plasma is higher in SW-reared tilapia. Collectively, these studies suggest that the growth-promoting actions of SW rearing and of MT administration in tilapia may be linked to elevations in GH and/or prolactin (tPRL₁₇₇ and tPRL₁₈₈)levels.     

Growth Performance and Proximate and Fatty Acid Compositions of Channel Catfish, Ictalurus punctatus, Fed for Different Duration with a Commercial Diet Supplemented with Various Levels of Menhaden Fish Oil

A 15‐wk study was conducted to evaluate the effect of supplemental menhaden fish oil levels and feeding duration on growth performance and tissue proximate and fatty acid (FA) compositions of juvenile channel catfish, Ictalurus punctatus. Dietary fish oil levels had no effect on final weight gain, feed efficiency, and survival of channel catfish. Tissue lipid contents were directly correlated to dietary lipid levels, while moisture contents were inversely related to dietary lipid levels. Fillet moisture contents progressively decreased, whereas fillet lipid increased with increasing feeding duration. Significant increase in saturated and total n‐3 FAs and decrease in monoenoic and total n‐6 FA in whole body and fillet were observed at each incremental level of dietary fish oil. Percentages of n‐3 and n‐3 highly unsaturated fatty acids in fillet of fish fed the control and 3% fish oil diets decreased with increasing feeding periods, whereas those of fish fed 6 or 9% added fish oil diets remained stable or increased. Ratios of n‐3/n‐6 were statistically comparable throughout the 15‐wk feeding. When expressed in terms of mg/g of fillet, the highest concentration of n‐3 was obtained in fillets of fish fed the 9% added fish oil diet for 15 wk.