Features of the species composition and structure of fish communities in small anthropogenic reservoirs with different content of dissolved mineral nitrogen

In 22 small anthropogenic reservoirs with an area of 0.4 to 62 ha located in the territory of the Udmurt Republic, individuals of different fish species were captured and water samples were taken in late spring for analysis of NO3–, NO2– and NH4+ content. In many reservoirs, concentrations of ammonium exceed the maximum permissible according to the fishing standards for water quality, and in some this is also the case with nitrites. Ponds with zooplanktophages (bleak Alburnus alburnus (L.) and belica Leucaspius delineates (Heckel)) present in fish communities were statistically significantly different in the increased content of total dissolved mineral nitrogen from reservoirs where these two fish species were not registered. In perch and roach reservoirs, the numerical proportion of river perch Perca fluviatilis was negatively and statistically significantly related to the level of their contamination with nitrogen ionic forms.

Openness of Fish Habitat Matters: Lake Pelagic Fish Community Starts Very Close to the Shore

Fish communities differ significantly between the littoral and the pelagic habitats. This paper attempts to define the shift in communities between the two habitats based on the European standard gillnet catch. We sampled the benthic and pelagic habitats from shore to shore in Lake Most and Římov Reservoir (Czech Republic). The 3 m deep pelagic nets were spanned across the water body at equal distances from two boundary points, where the depth was 3.5 m. The benthic community contained more fish, more species, and smaller individuals. The mild sloped littoral with a soft bottom attracted more fish than the sloping bank with a hard bottom and less benthos and large Daphnia. The catch of the pelagic nets was dominated by eurytopic fish—rudd (Scardinius erythrophthalmus) and roach (Rutilus rutilus) in Most and bleak (Alburnus alburnus) in Římov. With the exception of one case where overgrown macrophytes extended the structured habitat, the largest shift from the benthic to the pelagic community was observed only in the first pelagic gillnet above the bottom depth of 3.5 m. Open water catches were relatively constant with small signs of decline towards the middle of the lake. The results indicate that the benthic gillnet catch is representative of a very limited area and volume, while most of the volume is dominated by the pelagic community. This has important consequences for the assessment of the community parameters of the whole lake following the European standards for gillnet sampling design.

POTENTIALLY TOXIC ELEMENTS IN LOWLAND GREAT MORAVA RIVER – BIOINDICATION WITH BLEAK (ALBURNUS ALBURNUS)

The utilization of fish bioindicators has become of crucial importance for ecosystem contamination assessment. Bleak (Alburnus alburnus) is a widely distributed epipelagic fish species characterized as very active with fast metabolism which can lead to a high accumulation of pollutants in tissues. Bleak is easy to sample, identify in the field by morphological characteristics, and easy to work within the laboratory. This study deals with the bleak sensitivity in detecting the pressure of the potentially toxic elements (PTEs) in the large lowland Great Morava River. The Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sn, and Zn were estimated in whole body composite (wbc) of bleak. The study was conducted at Great Morava River, near the city of Paraćin in Serbia. The highest concentrations of essential elements Zn and Fe were detected. The most toxic elements As and Hg were below detection limits. The metal pollution index (MPI) was 0.39. In large lowland rivers, point sources of pollution such as municipal wastewaters of smaller settlements usually have only local impact due to high dilution by the main watercourse. Since bleak is a site-specific species, results in this study indicated that this stretch of the Great Morava River is slightly affected by PTEs. None of the elements above the maximum permitted concentrations (MPC) in fish meat for use in the human diet, prescribed by the Official Gazette and European Commission Regulation, were not recorded.

Regular Intergeneric Hybridization of Leuciscine Cyprinids (Cyprinidae, Leuciscinae) in the Dnipro Affluant

The large-scale hybridization of fishes of the subfamily Leuciscinae in the subordinate systems of the Dnipro River basin is presented by the data on two pairs of species, roach Rutilus rutilus × bream Abramis brama, and bleak Alburnus alburnus × rudd Scardinius erythrophthalmus. The hybridization and occurrence of F1 hybrids are confirmed with allozyme spectra and morphological characters on series of samples. A complete morphometric analysis of the characteristics of bleak and rudd hybrids was performed. The paper discusses the intergeneric hybridization in nature, which is a unique phenomenon characteristic only of some groups of cyprinids. The most likely reason is the overestimation of the taxonomic status of European cyprinids, which is confirmed by the insignificant level of intergeneric genetic divergence.

Interpopulation Variability in Dietary Traits of Invasive Bleak Alburnus alburnus (Actinopterygii, Cyprinidae) Across the Iberian Peninsula

The bleak Alburnus alburnus is native to most of Europe. This cyprinid fish is a successful invader in the Iberian Peninsula. No studies exist on its foraging strategies on a large scale for this ecoregion. The aim of the present study was to compare dietary traits of invasive bleak among the main Iberian rivers and a ‘reference’ native bleak population from France. Bleak were sampled during May–June 2019 from the Iberian Rivers Ebro, Tagus, Guadiana, Segura and Guadalquivir and the River Saône (France). Diptera larvae and zooplankton were common food categories in the River Saône. Insect nymphs were more important in the River Ebro. The intake of plant material was higher in the River Tagus. Flying insects were more consumed in the River Guadiana. Nektonic insects were important in the River Guadalquivir. Detritus was a frequent food category for all populations, in terms of occurrence and mass. Dietary parameters followed a unimodal response in relation to the latitudinal gradient, with the maximum values for the Tagus and Guadiana populations. Overall, results suggest that this wide interpopulation variability will contribute to the species’ successful establishment throughout Mediterranean Europe, which poses a serious risk to its highly valuable native fish fauna.

Morphobiological characteristic of bleak Alburnus Alburnus (Cyprinidae) of the River Alei (South-East Western Siberia)

The results of a study of the morphobiological parameters of the bleak Alburnus alburnus of the river Alei of the Altai Territory are presented. Data on the size-age structure and fertility are presented. According to some morphometric characteristics, significant differences between females and males were revealed.