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This article presents the results of a study of the dietary composition of juvenile Atlantic sturgeon caught in the Drwęca River and in Maltańskie Reservoir. Among the fish caught in the Drwęca, 67% had empty digestive tracts. In terms of numbers, the greatest share of the dietary composition of juvenile sturgeon from the Drwęca River was of Oligochaeta and larval Chironomidae, while the greatest weight contribution was made by larval Trichoptera. Larval Chironomidae, Oligochaeta, and Simuliidae were the most frequent components of sturgeon food. In comparison to the diet of fish from the Drwęca River, that of the fish caught in the Maltańskie Reservoir was more homogeneous as it was comprised exclusively of flies. Larvae of the genus Chironomus dominated numerically, followed by those of Procladius sp., Einfeldia sp., and Polypedilum sp. The analysis of juvenile Atlantic sturgeon food composition indicated that benthic organisms are the most important dietary component. In the natural lowland river the food spectrum of the juvenile Atlantic sturgeon was much wider than that of the fish in the dam reservoir.
This paper presents the karyotype and external morphology of larva, pupa and adult male of Stictochironomns sticticus (Fabricius, 1781) from Poland. The species of the genus Stictochironomus are generally identified on the basis of pupal and adult morphology. However, the species described in this paper has species-specific markers in the salivary gland chromosomes which allow identification at the larval stage. Karyological markers are evaluated for the Polish population in comparison with other European populations and Stictochironomus species.
A rearing experiment was focused on the effect of the type and diet composition on the European grayling (Thymallus thymallus L.) eggs quality, expressed by the embryos survival to the eyed-egg stage. Three feeding variants were analyzed. Spawners from group I were fed exclusively trout feed, group II received trout feed with maggots and fish in group III foraged on natural feed. A statistically significantly higher survival rate was determined for the eggs produced by group III spawners (84.57%) compared to the other two variants: 48.44% for group I and 56.00% for group II (the Tukey’s post hoc test, P < 0.05).
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