Artificial off-season spawning of Eurasian perch Perca fluviatilis L.

The aim of the study was to conduct off-season spawning of perch, Perca fluviatilis L. Spawners were obtained in late September from Lake Kortowskie. The fish were transported to the hatchery and divided into two size groups: G1 - small fish (30-70 g), and G2 - large fish (200-400 g). All males from G1 group spermiated after a two-month period of photo-thermal stimulation, but only 25% of the males from G2 group produced milt. Better results were obtained with fish that were stimulated after three months of chilling. All the stimulated males spermiated and produced higher volumes of milt. The best results, defined as ovulation success and embryo survival to the eyed-egg-stage, as well as spawner survival rate, were obtained with large females (G2-B) stimulated with a double dose of hormone (2 Ovopel pellets kg^-1). The egg strands obtained from females from group A (small and large fish stimulated with GnRHa and metoclopramide at 0.1 and 1 pellet kg^-1after 24 hr) were usually fragmented. All females responded to the hormonal injections after 4 to 5 days.