17 meristic and morphometric features were studied in the bleak in the waters of Międzyodrze. Noticeable positive or negative allometry was observed in the growth of head length, horizontal eye diameter, pelvic fins length, body height, and in the distance between pelvic fins and anal fin. In the light of the studied features, the bleak in Międzyodrze places itself in a transitional position between the lake populations and the riverine and estuarine populations.
Morphomechanical study on the changes taking place in the course of the embryonic development of the bleak (Alburnus alburnus L.) conducted on tlle live fish in vertical and horizontal light beams, revealed that the oocyte (yolk mass) occupies some 30% of the entire egg′s volume, while the remaining 70% is occupied by the perivitelline space. The blastodisc and subsequently the embryo and the larva before the hatching always take up lateral position in the egg. No lipid droplets (structural fat), commonly occurring in the eggs of the other teleost fishes are present in the yolk mass of the bleak eggs. Biological justification of the above extraordinary phenomena as well as their adaptive importance is discussed.
The rate growth of bleak in Międzyodrze-the wetland located in the lower course of the Odra River above Szczecin-was estimated with use of back-calculations. The fish reaches 59.3 mm in length in the first year of life, 89.1 in the second year, 115.8 mm in the third, and 131.5 mm in the fourth year of life (SL). Females are on the whole larger than males of the same age.
Zinc present in water penetrates into the organism of a fish either directly, through the skin and gills, or indirectly, with food taken into the alimentary canal. The toxocity of this metal is associated with the transporting function of blood, which distributes it over the whole organism. The aim of this paper was to assess the zinc content in water and bottom sediments collected from the Dunajec River, and also in selected organs of bleak (Alburnus alburnus L.). The bioaccumulation factors for this element in the muscles, liver, skin and bones of the fish were calculated from the results of the research, which was carried out in 2011. Samples of water and bottom sediments were collected twice, in July and October, at 5 research points located in Szczepanowice, Janowice, Wróblowice, Lusławice, and Zakliczyn. Twenty-nine specimens of bleak were provided by members of the Polish Angling Association (PZW — Polski Związek Wędkarski), from catches performed in the second half of July. The zinc concentration in the samples was determined by inductively coupled plasma atomic emission spectrometry at a wavelength of 206.200 nm, conducted on an Optima 7600 DV spectrometer made by Perkin Elmer. The limit of detection for zinc was 5.9 μg · dm-3. High concentrations of zinc in the water were found, indicative of anthropogenic enrichment of the river with this element. The zinc content in the analysed sediments was below the geochemical background value for bottom sediments in Poland. Zinc concentrations in the fish varied within a range from 152.6 to 352 mg ∙ kg-1 in the skin, from 158.8 to 271.3 mg ∙ kg-1 in the bones, from 27.32 to 97.35 mg ∙ kg-1 in the muscles, and from 82.39 to 230.7 mg ∙ kg-1 in the liver. The mean content of zinc in individual organs decreased in the following order: skin > skeleton > liver > muscles. Zinc concentrations in individual organs of the fish were comparable with the ones determined eslewhere in environments polluted with this element.
The presence of carotenoids in several body parts of three planktonophagous species was investigated by means of columnar and thin-layer chromatography.
During a survey on myxosporean parasites of cyprinid fishes in Hungary, Myxobolus infections were found in the cartilaginous rays of the gill filaments in roach (Rutilus rutilus) and bleak (Alburnus alburnus). Myxobolus spp. causing the infections were studied by morphological, histological and molecular methods. Small plasmodia surrounded by chondrocytes contained relatively few spores which differed from each other and from the known Myxobolus spp. both in their morphology and 18S rDNA sequences. Both species, described as M. feisti sp. nov. and M. susanlimae sp. nov., are characterised by a specific cartilaginous histotropism.