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Summary Gillnet size selectivity was studied for freshwater fish species, based on experimental fishing trials carried out with multimesh gillnets in lentic freshwater systems in Northern Greece. Selectivity estimates were based on a large range of mesh sizes, i.e. more than 10 different mesh sizes ranging from 8 to 90 mm bar length. Results showed that the model, in which both mean and standard deviation of the curve were defined as a linear function of the mesh size, revealed the best fit. For seven (i.e. Αlburnus sp. Volvi, Aspius aspius, Carassius gibelio, Lepomis gibbosus, Pachychilon macedonicum, Squalius prespensis and Vimba melanops) of the 11 studied species and the hybrid (Alburnus belvica × Rutilus prespensis), gillnet selectivity parameters were estimated for the first time, contributing to the evaluation of gillnet fisheries' impacts on fish species populations and consequently to fisheries management and species conservation.

Summary The aim of the study was to determine gonadal maturity in male and female vimba after induced spawning in the years 2001 throughout 2004, based on spawners derived from an anadromous population obtained from the Barycz River. For these 4 years, fry derived from each successive spawning were raised in carp ponds at the Experimental Hatchery Centre of the Polish Angling Association in Szczodre, Poland. In February 2005, gonads were collected from males and females and their maturity determined after histological preparations. Additionally, in females the diameters of oocytes undergoing trophoplasmic growth were determined and compared. Histological analysis showed that all females had gonads at maturity stage IV, except the youngest fish, in which maturity stage I was determined. It was also shown that the size of oocytes undergoing trophoplasmic growth was related to age: the older the females, the greater the proportion of large-diameter oocytes. In addition, some 2-year-old females had a considerable proportion of oocytes undergoing trophoplasmic growth despite being at stage IV of ovarian maturity. Among males, 2- to 4-year-olds had gonads at maturity stage III, in which the spermatogenesis process was active. One-year-old males had testes at maturity stage II, with visible spermatogonia entering meiotic divisions. When keeping vimba under pond conditions, only 2 years are needed to obtain a mature spawner from a spawning school. The older the school, the higher the probability that a greater number of spawners will enter spawning.