Zoobenthos represents the basic and often sole diet component of juvenile salmonid fish that live in small streams or brooks. Abundance and biomass of benthic fauna often determine the body condition, development potential, and survival of the fish. This article presents the results of a benthic macrofauna survey carried out in three small rivers in terms of its availability as food base for juvenile salmonid fish. It has been demonstrated that such streams, due to their small sizes, are unsuitable for routine stocking. However, water quality and abundance of food organisms make such streams important in terms of stream rearing of juvenile salmonids. The food factor is reflected by characteristic macrofauna communities. We have found 5 classes of invertebrates in all the streams. Mean abundance ranged between 873.5 and 9967.7 indiv.·m^–2, with a high proportion of Gammaridae, exceeding 90%.

Individual weight, total length, condition, and growth rate was determined in the vendace caught in spring, summer, and autumn of 1999–2000 from 4 Western Pomeranian lakes: Miedwie, Ińsko, Woświn, and Glinno, the lakes differing in their trophic status and morphometry. The vendace caught in the mesotrophic lakes Miedwie and Ińsko showed better condition and higher length and weight growth rates, compared to those parameters revealed by the vendace from the eutrophic lakes Woświn and Glinno.

During the period from October 2002 and November 2003, ovaries of 4–5 year old hybrids obtained as a result of reciprocal hybridization of rudd and carp bream (rudd ♀ x carp bream ♂, carp bream ♀ x rudd ♂) were histologically examined. In both groups of hybrids: rudd ♀ x carp bream ♂ and carp bream ♀ x rudd ♂, females with autumn-spring and spring period of vitellogenesis were found; in the carp bream ♀ x rudd ♂ the majority represented the spring vitellogenesis period (P < 0.05). In both groups of hybrids, during the period preceding reproduction and after reproduction, females showed characteristics to both spawn types: total spawners and batch spawners. Studies show that periods of vitellogenesis: autumn-spring and spring as well as spawn types: total and batch characteristic for carp bream and rudd respectively appear in both genetic lines of their hybrids (rudd ♀ x carp bream ♂ and carp bream ♀ x rudd ♂), and that the frequency of appearance of females with spring vitellogenesis period is higher when carp bream is the maternal species and rudd the paternal one. The results of studies suggest that females representing a different spawn type or vitellogenesis period found in population of crossing fish species can be the hybrids of those species.