One of the most important problems in cyprinid aquaculture is obtaining good quality gametes. For this reason, many hormonal treatments are used to stimulate gamete maturation. In some cases, the changing of spawning time is needed, especially when many fish species are spawned in the hatchery. Earlier spawning gives the possibility to produce longer and heavier juveniles, and this is important for farm economy.

In this project, some wild cyprinid species were subject to tests on reproduction before the normal spawning season: asp (Aspius aspius), dace (Leuciscus leuciscus), ide (Leuciscus idus) and chub (Leuciscus cephalus). Spawners were caught in October from natural waters. Fish were transported to the hatchery and kept in 1000-L tanks with controlled temperature and photoperiod. During first few weeks, the water temperature and light conditions were quickly decreased to 2°C and 2hrs of light per day, respectively. Fish were kept under these “Winter” conditions for the next few weeks. Later, both environmental conditions were increased to try to induce spawning in January. The temperature and photoperiod regimes were different for different species. Before spawning, fish were kept in water temperatures similar to those at season-time spawning. Fish from both sexes and all species were divided into three groups, two experimental and one control. After five days of acclimation to the optimal temperature, the fish were treated with hormonal injections of common carp pituitary (Argent, USA) extract with the addition of hCG, or GnRHa with dopamine antagonist (ovopel pellets). All spawning agents were prepared with 0.9% NaCl: pituitary extract was homogenized, hCG dissolved and ovopel pellets were pulverized in a mortar and then dissolved. Injections of hCG were intramuscular in the dorsal area of the body. Injections of pituitary and ovopel extracts were intraperitoneal at the base of the pelvic fin. Before manipulations, fish were anaesthetized with 2-phenoxyethanol (0.5mg.l^-1). Time intervals between injections are 24 hrs.