Interactive Effects of Dietary Ascorbic Acid and Density on Reproductive Performance of Rainbow Trout (Oncorhynchus mykiss)

The aim of the present study was to investigate the effects of ascorbic acid and density on reproductive performance and steroid hormones in rainbow trout (Oncorhynchus mykiss). In this regard, six treatments were considered included three diets containing 0, 100, and 1000mg ascorbic acid as L-ascorbyl-2-polyphosphate per kilogram of food in contrast to two densities 4.33kg/m3 and 2.16kg/m3. Triplicate groups of fish were fed one of the test diets for 16 weeks. A total of 81 females with an average weight of 812.1±1.5g were introduced to tanks (910 liters). At the end of the 16th week and when preparing fish for spawning, from each replication of high and low densities, 4 and 2 fish after bleeding of fish to measure the concentrations of progesterone, testosterone, and estradiol were spawned. After that, reproductive parameters such as work fecundity, ova per gram, and ova diameter were measured and then fertilized. During the incubation period, fertilization and mortality rates were recorded. The results showed the interaction between ascorbic acid and density and also the significance of this effect in reproductive parameters (number per gram of egg, oocyte diameter, coagulation, and fertilization percent; p<0.05). In the case of steroid hormones, the effect of treatments on the amount of each of the three hormones and their interaction on the level of estradiol and testosterone were significant (p<0.05), but the effect of density and diet on progesterone was not significant (p>0.05). The results of this study confirm the use of higher levels of ascorbic acid in breeders compared to grow-out period and also the positive role of this vitamin in reproductive indices.