Comparative study of Gymnocephalus cernuus (Linnaeus, 1758) and G. baloni Holcik & Hensel, 1974 (Pisces, Percidae)

In the comparative study of Gymnocephalus cernuus and G. baloni we searched for differences in growth, habitat and feeding between the two species in support of their distinctness. significant differences were found in both habitat and feeding, whereas growth was more or less similar. G. baloni is bound to hiding places located in flowing water. In vegetative periods it occurs solitary and in generative in pairs. G. cernuus lives in shoals in the whole season, occuring mostly in the open, still parts of waters near to the bottom. The food of the two ruffe species mostly consists of the characteristic macroinvertebrates of their habitat. The body pattern, the number of opecular spines and the cut on the membrane between AI and AII were found to be the most useful characters in identification

Application of an electrified benthic frame trawl for sampling fish in a very large European river (the Danube River) – Is offshore monitoring necessary?

The organization of fish assemblages in offshore, deep channel habitats is poorly known in very largerivers compared with shoreline, littoral areas. We report on the parameters and testing of an electrifiedbenthic frame trawl (EBFT), developed for monitoring the distribution and abundance of benthic fishesin the Danube River, Hungary. We also compare the results of the benthic main channel survey witha shoreline electrofishing (SE) data set. Altogether 33 species were collected offshore during the 175trawling paths (500 m long each). Both sample based and individual based rarefaction showed that nighttime SE detected significantly more species with increasing sampling effort than day time trawling ofoffshore areas. However, offshore surveys detected sterlet Acipenser ruthenus, which could not be detectedby SE, even using extreme high sampling effort. Offshore trawling also proved the common occurrenceand high abundance of the strictly protected endemic Danube streber Zingel streber in the river, whichproved to be extremely rare in SE catches. The EBFT caught larger/older individuals of many species thanSE, and indicated diverse size/age structure for many species offshore. Our survey revealed that offshoreareas are intensively used by a variety of species, which occur relatively even, but with variable abundancein the Danube River. We suggest that even a relatively small (i.e. 2 m wide 1 m high) EBFT can be a veryuseful device for monitoring offshore fish assemblages in very large rivers and provide important datafor bioassessment and conservation purposes

Note on the special fillet fatty acid composition of the dwarf carp (Cyprinus carpio carpio) living in thermal Lake Hévíz, Hungary

Fatty acid (FA) composition of the fillet and the intestinal content of dwarf common carp (Cyprinus carpio carpio) living in Lake Hévíz was determined in wintertime collected samples and results were compared to widespread literature data on carp. Fillet FA profile of the thermally adapted (28 oC) Hévíz dwarf carps differed from profiles originated from divergent culture and feeding conditions in the overall level of saturation. Fillet myristic acid proportions largely exceeded all literature data in spite of poor dietary supply. Fillet fatty acid results indicate the effects of thermal adaptation (high saturation level) and the correlative effects of feed components rich in omega-3 fatty acids, with special respect to docosahexaenoic acid. With the application of discriminant factor analysis the Hévíz sample was accurately differentiated from the literature data on carp fillet fatty acid profile, mostly based on C14:0, C18:1 n9, C18:2 n6, C20:1 n9 and C20:4 n6 FAs. In summary, fillet FA profile suggested thermal adaptation, location specificity and the ingestion of algal and bacterial material

Effects of a Nuclear Power Plant Warmwater Outflow on Environmental Conditions and Fish Assemblages in a Very Large River (the Danube, Hungary)

Direct or indirect effects of nuclear power plants' (NPPs) warmwater effluents on the structure of biotic assemblages are poorly known in very large rivers. We examined changes in physical habitat structure, temperature condition and their possible effects on the structure of Danubian fish assemblages due to the outflow of the Paks NPP's warmwater channel, in Hungary. Seasonal surveys conducted both upstream and downstream from the outfall showed that its hydromorphological effects were generally local and comparable to natural or other anthropogenic hydromorphological changes. The effect of the returned cooling water was more apparent in the seasonally recorded surface water temperatures and depended highly on the spatial positioning of the sampling sites. However, environmental and spatial variables accounted only for a low amount of variance in case of both shoreline and offshore fish assemblage data. Overall, we found that the outflow exerted only a local scale effect on the structure of Danubian fish assemblages. Rather, fish assemblages varied largely both inshore and offshore, which dynamics overruled any effects of the artificially elevated temperature. Our study highlights the importance of the assessment of hydrogeomorphological variability of rivers and their influence on fish assemblage variability when examining spatial effects of thermal pollution

Impact of environmental and genetic factors on the scale shape of zebrafish, Danio rerio (Hamilton 1822): A geometric morphometric study

Intraspecific morphological variability may reflect either genetic divergence among groups of individuals or response of individuals to environmental circumstances within the frame of phenotypic plasticity. Several studies were able to discriminate wild fish populations based on their scale shape. Here we examine whether the variations in the scale shape in fish populations could be related to genetic or environmental factors, or to both of them. In the first experiment, two inbred lines of zebrafish Danio rerio (Hamilton 1822) reared under identical environmental conditions were compared. Secondly, to find out what effect environmental factors might have, offsprings were divided into two groups and reared on different diets for 12 weeks. Potential recovery of scales from an environmental effect was also assessed. Experimental groups could successfully be distinguished according to the shape of scales in both experiments, and the results showed that both genetic and environmental factors may notably influence scale shape. It was concluded that scale shape analysis might be used as an explanatory tool to detect potential variability of environmental influences impacting genetically homogeneous groups of fish. However, due to its sensitivity to environmental heterogeneity, the applicability of this technique in identifying intraspecific stock membership of fish could be limited