The effects of recreated instream and ecotone structures on the fish fauna of an epipotamal river

Investigations of fifteen sections of seven Austrian epipotamal (barbel region) streams between 1981 and 1984 demonstrate the impact of instream river bed structures on fish communities. Reduced spatial heterogeneity due to river straightening resulted in decreasing species number, diversity, stock density and biomass. Reincreased variability of the river bed in the frame of a subsequent restructuring project improved all community-specific values significantly within a 3-year investigation period (1988–1990). Besides the regained habitat variability in form of riffle pool sequences and other instream structures, the newly created riparian zones obviously provided important niches, e.g. as refuge areas during flooding and as nursery grounds for fish fry. The positive effects of the recreated land/water ecotone are discussed with respect to river restoration projects.     

Cell cultures derived from early zebrafish embryos differentiate in vitro into neurons and astrocytes

The zebrafish is a polular nonmammalian model for studies of neural development. We have derived cell cultures, initiated from blastula-stage zebrafish embryos, that differentiate in vitro into neurons and astrocytes. Cultures were initiated in basal nutrient medium supplemented with bovine insulin, trout serum, trout embryo extract and fetal bovine serum. After two weeks in culture the cells exhibited extensive neurite outgrowth and possessed elevated levels of acetylcholinesterase enzyme activity. Ultrastructural analysis revealed that the neurites possessed microtubules, synaptic vessicles and areas exhibiting growth cone morphology. The cultures expressed proteins recognized by antibodies to the neuronal and astrocyte-specific markers, neurofilament and glial fibrillary acidic protein (GFAP). Poly-D-lysine substrate stimulated neurite outgrowth in the cultures and inhibited the growth of nonneuronal cells. Medium conditioned by the buffalo rat liver line, BRL, promoted the growth and survival of the cells in culture. Mitotically active cells were identified in cultures that had undergone extensive differentiation. The embryo cell cultures provide an in vitro system for investigations of biochemical parameters influencing zebrafish neuronal cell growth and differentiation.     

Population structure and impact of supportive breeding inferred from mitochondrial and microsatellite DNA analyses in land-locked Atlantic salmon Salmo salar L.

Four tributaries of Lake St-Jean (Québec, Canada) are used for spawning and juvenile habitat by land-locked Atlantic salmon. Spawning runs have drastically declined since the mid-1980s, and consequently, a supportive-breeding programme was undertaken in 1990. In this study, we analysed seven microsatellite loci and mtDNA, and empirically estimated effective population sizes to test the hypotheses that (i) fish spawning in different tributaries form genetically distinct populations and (ii) the supportive breeding programme causes genetic perturbations on wild populations. Allele frequency distribution, molecular variance and genetic distance estimates all supported the hypothesis of genetic differentiation among salmon from different tributaries. Gene flow among some populations was much more restricted than previously reported for anadromous populations despite the small geographical scale (40 km) involved. Both mtDNA and microsatellites revealed a more pronounced differentiation between populations from two tributaries of a single river compared with their differentiation with a population from a neighbouring river. The comparison of wild and F₁-hatchery fish (produced from breeders originating from the same river) indicated significant changes in allele frequencies and losses of low-frequency alleles but no reduction in heterozygosity. Estimates of variance and inbreeding population size indicated that susceptibility to genetic drift and inbreeding in one population increased by twofold after only one generation of supplementation.     

Dwindling food-fish species and fishers' preference: problems of conserving Lake Malawi's biodiversity

Most of Malawi's popular food-fish species are in decline. The fishers attribute this decline to overfishing, changes in climate, inadequate fishing technology and supernatural powers. Sedimentation of the lake and rivers due to poor agricultural practices, which can also be implicated in the demise of Malawi's fisheries, was not recognized by the fishers. This study tested and confirmed that the fishers would readily switch to exploiting ornamental fish (Mbuna) for subsistence and cash if the more favoured food-fish species continued to dwindle. However, as most of the Mbuna species are localized to specific rocky habitats and are endemic to certain parts of the lake, they may be vulnerable to overfishing. To safeguard Lake Malawi's rich fish species diversity: (i) alternative economic opportunities for the lakeshore people should be identified, evaluated and promoted to alleviate the fishing pressure, (ii) the Department of Fisheries should collaborate with local fishermen in promoting sustainable fish utilization, e.g., through public campaigns aimed at sensitizing fishermen on the status of the fisheries and the vulnerability of some fish communities to overfishing and environmental degradation, and (iii) the degree of Mbuna exploitation, now that the popular food fishes are in decline, should be monitored and, where necessary, regulated to promote sustainability.     

Genetic variability in the European minnow,Phoxinus phoxinus (L.)

An electrophoretic study of genetic variation at 11 loci was performedfor a population of European minnows, Phoxinus phoxinus (L.). Ten loci, EST-1 ^*, EST-2 ^* EST-3 ^*,GPD-1 ^*,GPD-2 ^*,GPI-1 ^*,GPI-2 ^*,MPI ^*,6PGD ^* and PGM ^* were polymorphic. IDH ^*wasmonomorphic. The mean number of heterozygotic loci over all 176 fish was 3.05 ± 0.104(SE). Observed mean heterozygosity was 0.28±0.058(SE) and expected mean heterozygosity was 0.27±0.054(SE). EST-2 ^*, EST-3 ^* andPGM ^* were not in Hardy-Weinberg equilibrium. Length,condition, parasite numbers or male breeding characters, i.e. red colorationand tubercles, were not influenced by single enzyme loci.     

Influence of fish on the breeding of the red-necked grebe Podiceps grisegena (Boddaert, 1783)

I determined whether selection of breeding sites by thered-neckedgrebe Podiceps grisegena (Boddaert, 1783) was affectedbycompetition for food with fish. During 1987–89, ten ponds inScania, southern Sweden were investigated, five with(breedingsites) and five without breeding red-necked grebe(non-breedingsites). I quantified the biomass of fish and macrozoans(here:larger invertebrates and small vertebrates) and measured thephysical and chemical conditions of the ponds.Breeding sites had significantly lower relative fish abundancethannon-breeding sites. They were either devoid of fish or hadonly nine-spined sticklebackPungitius pungitius. The biomass (dry weight) ofmacrozoans,many of which represent a food resource for grebes, was 16timesgreater at breeding than at non-breeding sites. The physicalandchemical conditions of the ponds did not differsignificantly.These results are consistent with the hypothesis thatcompetitionfor macrozoans occurs between red-necked grebe and fish andthat adense population of many fish species caused red-necked grebestoavoid otherwise acceptable breeding sites.     

Multiple α2-Adrenoceptor Signalling Pathways Mediate Pigment Aggregation Within Melanophores

It has previously been shown that α₂-adrenoceptors (α₂-ARs) mediate pigment granule (melanosome) aggregation in melanophores of the teleost fish Labrus ossifagus. The present investigation scrutinized the signalling mechanisms of melanosome aggregation induced by sympathetic nerve stimulation or by exogenous addition of α-AR agonists and cAMP analogues. The following was observed: i) nerve-induced melanosome aggregation was associated with a rapid decrease in the cAMP level; ii) noradrenaline or medetomidine (an α₂-AR agonist) caused melanosome aggregation and reduced the cAMP content; iii) RP-S-CI-cAMP, a membrane-permeating inhibitor of protein kinase A induced melanosome aggregation; and iv) B-HT 920 (an α₂-AR agonist) and methoxamine (an α₁-AR agonist) induced melanosome aggregation, although they did not reduce cAMP. It has been suggested that in some teleost species α₁-ARs mediate melanosome aggregation by increasing the level of intracellular calcium. However, we found that the effect of methoxamine in melanophores from Labrus ossifagus could be blocked by yohimbine (an α₂-AR antagonist) but not by equimolar concentration of prazosin (an α₁-AR antagonist). Furthermore, 1 μM ionomycin (a calcium ionophore) did not induce melanosome aggregation. Our findings therefore do not indicate that α₁-ARs and/or an increase in intracellular calcium mediate melanosome aggregation in Labrus ossifagus. Our results suggest that α₂-AR-mediated melanosome aggregation is induced by multiple signalling pathways. One of these involves a reduction in cAMP, but none involves an increase in intracellular calcium.     

Sperm motility in turbot,Scophthalmus marimus: initiation of movement and changes with time of swimming characteristics

Synopsis Turbot sperm motility is observed using dark field microscopy and stroboscopic illumination combined with video recording. Sperm motility is triggered by dilution of spermatozoa in sea water or in non ionic media (glucose or saccharose), presenting osmotic pressure ranging from 300 to 2100 mOsmol. The percentage of motile spermatozoa reaches 100% under conditions of osmotic pressure of 300 to 1100 mOsmol and pH close to 8.0. In full sea water, glucose or saccharose solutions an agglutination of spermatozoa is observed; this is prevented by addition of bovine serum albumin (5 mg ml^–1). Immediately after transfer in activation solutions, 100% spermatozoa are motile in most samples freshly stripped. This percentage drops suddenly between 15 and 30% after 70 to 100 sec. The beat frequency remains at a constant value of 50 Hz during 40 s post activation and then drops suddenly between 15 and 30 Hz. The spermatozoa velocity is about 200 micrometers s^–1 during 30 to 40 s and then declines to a stable value of 100 micrometers s^–1 at 50 s post activation. After 1.20 mn, more and more spermatozoa become motionless. The minimum calculated and averaged distance covered during 1.20 min, is about 12 mm. The high performances of turbot spermatozoa motility are interpreted as a compensatory mechanism for the low sperm production.     

鳜鱼的耗氧率及其池塘养殖

本文较详细地报道了鳜鱼的耗氧率和窒息点,并对鳜鱼和作其饲料的鱼同池饲养的可能性进行了探讨。结果表明,鳜鱼耗氧量和体重正相关（ｒ＝０．９９）,耗氧率与体重反相关（ｒ＝－０．９７）;在水温２０℃,鱼种耗氧率约为０．１４ｍｇ／ｇ．ｈ．,成鱼约为０．１２ｍｇ／ｇ．ｈ．;耗氧量和耗氧率均与水温正相关（ｒ＝０．９０,ｒ＝０．９４）,水温１３—３０℃时,体重２３０±１１．７ｇ的鳜鱼。耗氧量为１４．３１—４２．１３ｍｇ／尾。ｈ．,耗氧率为０．０５９—０．１７５ｍｇ／ｇ．ｈ．;鳜鱼耗氧率昼夜变化与家鱼相反,黄昏至凌晨是高峰期,为０．１２—０．１５ｍｇ／ｇ．ｈ．（Ｔ＝２０℃）,白天是低谷期,为０．０７—０．１０ｍｇ／ｇ．ｈ;;鳜鱼的窒息点与家鱼类较接近,变化范围为０．４５—０．７６ｍｇ／Ｌ;鳜鱼和作其饲料的鱼在同一池塘中饲养,既可持续不断地提供鳜鱼充足的适口饵料,又简单易行,成本低,效益高,有较大的价值。     

四川55种鱼生活史型的研究

四川５５种鱼生活史型的研究刁晓明,罗一兵李波（西南农业大学水产系,重庆６３０７１６）（重庆大学计算机系,６３００００）ＬｉｆｅＨｉｓｔｏｒｙＰａｔｔｅｒｎｓｏｆ５５ＦｉｓｈＳｐｅｃｉｅｓｉｎＳｉｃｈｕａｎ￥ＤｉａｏＸｉａｏｍｉｎｇ;ＬｕｏＹｉｂｉｎｇ...