The upper stretch of the Pek River is located in proximity to one of the largest mining sites in Serbia. To estimate the influence of copper mining on river biota, the quantitative and qualitative macroinvertebrate community structure was analyzed, and the ecological status of the river was assessed using standard biological indices. Data was gathered at 6 sites along the river. A total of 75 macroinvertebrate taxa were recorded. The reference site had the highest number of recorded taxa (48) and a high biodiversity (diversity index H=2.3). In contrast, the lowest number of taxa (8), a low diversity index value (H=1.15), and a very poor overall ecological status were recorded at site 2, which is heavily influenced by mining discharge. The Ephemeroptera, Plecoptera and Trichoptera group (EPT) constituted 46.30% of the community at site 1 but was completely absent at site 2 where Diptera (70%) and Oligochaeta (20%) were dominant, reflecting a strong impact of the mining industry on the upper river stretch. A gradual improvement of water quality downstream of the pollution sources indicates that this medium-sized river has the capacity to overcome intensive pollution and to revitalize itself along its course.
Examination of brown trout seasonal diet variation and investigation of terrestrial prey importance in a food-rich stream using four indices of prey importance (number and weight abundance, frequency of occurrence, index of relative importance) revealed that aquatic prey constituted the major part of the diet (>90%) throughout the examined period. Despite Gammaridae being the most abundant in the environment, other less abundant organisms appeared to be important prey, including terrestrial organisms, with maximum consumption in September. The electivity index showed a positive selection of rare prey types; Tokeshi’s model revealed a specialist strategy for most of the population, except for those of 1+ age, who were inclining to generalist strategy. Diet diversity increased throughout April to October, and ages 1+ and 2+ exhibited a more diverse diet than older ages. Diet overlap between age classes was considerable, with less overlap observed in the later season. This pattern of differentiation in the diet of brown trout age classes and their feeding plasticity over seasonal scales, as observed in this food-rich stream, provides a starting point for further examination of this topic in streams with similar or different food richness and availability.
Background. A sampling of stomach and intestine content is usually performed by dissection of the gastrointestinal tract of fish. To avoid fish sacrificing, various non-lethal techniques have been developed and tested. Such sampling methods are very useful, especially for small populations and protected species. In this study, a modified syringe stomach flushing was applied on Oncorhynchus mykiss (Walbaum, 1792), and Salmo trutta Linnaeus, 1758, to test its efficiency in retrieving stomach content. Materials and methods. Water was injected repeatedly by a syringe through a silicone tube directly into the stomach of live fish to flush the content out. Afterwards, fish were dissected to collect residual stomach content. The efficiency of the method was assessed as the percentage of flushed content by weight and as the percentage of the number of flushed prey items, both in respect to the whole stomach content (100%). The relation between the fish body size (length and weight) and efficiency of flushing (expressed as the weight and number of flushed prey) was tested by linear regression. The sensitivity of the method was tested with respect to 25 designated prey types. The share of each prey type was compared in the pooled sample of flushed and residual content. Results. Collected stomach content was well preserved for identification of ingested organisms. From 25 designated prey types, 17 were 100% flushed, 4 over 90%, one over 80%, 2 were 44% effectively flushed (gastropods and caddisflies in stone cases), and 1 prey type was present only in the residual sample (Gordius sp.). The efficiency of the method assessed as the mean percentage of flushed content by weight was found to be 78.78%, while 91.99% of prey items were effectively flushed. Conclusion. The applied modification of syringe stomach flushing was found to be effective for investigation of stomach content of salmonid fish since (1) collected prey items were well preserved and easily identified; (2) the percentage of flushed prey items was high (91.99%); and (3) the method is easily applicable and inexpensive.
As data on the distribution of freshwater sponges (Porifera, Demospongiae, Spongillida) in Serbia are extremely scarce, we investigated the main Serbian rivers and lakes with respect to Porifera occurrence, for which 17 lotic and 11 lentic water bodies were selected. Sponges were found in 11 of 17 rivers (62 specimens in total) and in 3 of 11 lakes/reservoirs (seven specimens in total). Classical morphological spicule analysis was coupled with polymerase chain reaction (PCR) and gene sequencing for species identification. Among the 69 collected speci- mens, five sponge species of the family Spongillidae have been identified: Ephydatia fluviatilis (Linnaeus, 1759), Spongilla lacustris (Linnaeus, 1759), Ephydatia muelleri (Lieberkühn, 1856), Trochospongilla horrida Weltner, 1893, and Eunapius fragilis (Leidy, 1851). The most frequently found sponge in Serbian rivers was E. fluviatilis (45% of all specimens), while the least frequent was E. fragilis (6 % of all specimens). The Tisa river has the highest sponge diversity (four species). In lentic water bodies, only E. fluviatilis (four specimens) and S. lacustris (three specimens) were found. In general, sponges were infrequent and their abundance was low in Serbian fresh waters. While sponges seem to tolerate significant variations of physical and chemical parameters, some optimal values can be established.
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