The aim of this study was to determine the effects of dietary probiotics on reproductive performance, growth, haematological and biochemical parameters of female rainbow trout broodstock. A total of 60 broodstocks with an average initial weight of 2,267.4 ± 54.9 g were divided into four groups and three replicates in raceway ponds.Fish were fed with diets containing 0 (control), 1 × 10 9 (P1), 2 × 10 9 (P2) and 4 × 10 9 (P3) CFU probiotic per kg diet twice a day for 8 weeks before spawning season.Results revealed that higher levels of dietary probiotics (P3) enhanced protein efficiency ratio and decreased feed conversion ratio (p < .05). There were no significant differences in haematological and other growth parameters among different treatments. According to the results, probiotic-fed treatments had the lowest levels of cholesterol (237.7 ± 4.3 mg/dl) and the highest levels of total protein (11.3 ± 0.3 g/dl) and albumin (6.9 ± 0.3 g/dl), so that differences were found between P3 and control groups in all cases (p < .05). Based on the observations from reproductive parameters, the highest egg diameter, working and relative fecundities, fertilization and hatching rates, eyed eggs survival and alevins survival rates up to the absorption of the yolk sac were observed in P3 treatment (p < .05). Moreover, eyeing, hatching and yolk sac absorbing stages in P3 treatment were earlier than those in other treatments (p < .05). The results of present study demonstrated that probiotic supplementation improved reproductive performance and some growth and biochemical parameters in female rainbow trout broodstock and the best performance was observed in fish fed 4 × 10 9 CFU probiotic per kg diet. Due to an increase in egg production and egg size in probiotic-fed treatments, this feed additive can be used as a suitable ingredient to increase high-quality egg production in rainbow trout breeders. K E Y W O R D Sblood analysis, fecundity, growth performance, probiotic, propagation, salmonids | 99 AKBARI NARGESI Et Al.

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