Title of manuscript: The Optimization of Wide-Type Zebrafish, Danio rerio (Hamilton, 1822) Reproduction in Low Temperatures under Controlled Conditions

Zebrafish is popular aquarium fish and laboratory model species but some aspects of advanced spawning technologies, especially of reproduction and rearing in low temperatures (> 25 degrees C), which involve the production of high quality and viable gametes, should be studied. In the present study fish before spawning were reared at cold thermal regime: 19-20 degrees C. From three tested temperatures for fish spawning, the highest spawning effectiveness was noted at 23 degrees C. The highest rate of embryo survival was noted when the temperature in which the spawners were kept before spawning was the lowest (19 degrees C). In the spawning of small breeders groups, the number of males should be higher than the number of females. If the sex rate was 1:1, the lowest embryo survival was noted. From the breeding perspective fish of this species should be reproduced again shortly after the completed spawning a time between spawns should be 20 to 60 days if the spawners were kept at 19 degrees C. Keeping the fish between spawning periods more than 40 days results in a significant deterioration of quality of gametes, expressed as embryo survival. It was observed that spawners of this species produce viable gametes and spawn successfully every 20 days, during a few following spawning periods without changes of embryo survival.