اثر دفعات تخم‌ کشی و تراکم نگهداری تخم بر میزان ماندگاری تخم و لارو در ماهی قزل‌ آلای رنگین کمان [ Oncorhynchus mykiss (Walbaum, 1792)]

To determine the effects of spawning frequency and density of incubating eggs on the survival rates of eggs and larvae in rainbow trout, five different groups of broodstocks with varying spawning frequencies were stripped. After fertilization, the percentage of survival at different stages of development, from eying, hatching to free swimming fry stages and also growth rates of larvae were determined. Moreover, the effects of incubating egg density (4000, 7000, 10000 per tray) on the different developmental stages of egg through free swimming larvae for each group of broodstock was studied. The study was carried out in a completely randomized design as a 5*5*3 factorial arrangement with three replicates. The results indicated that survival and growth rates are significantly correlated with spawning frequency (P<0.05) so that, survival and growth rates from fertilization to free swimming fry in broodstocks at their third and fourth spawning period were significantly different from the results obtained for broods in the first, second and fifth or higher spawning periods (P<0.05). Although the holding densities had no significant effects on the growth rate of larvae from different broodstocks, the survival rates from fertilization to free swimming stage was affected by incubating density so that the significantly lower value was recorded for density of 4000 per tray (P<0.05). In general, the results indicate that eggs obtained from broodstocks at their third and fourth spawning years have a better performance than those obtained from younger and older spawners. Also, the low holding density of eggs could decrease the performance of the fertilized eggs during incubating period.