Effects of different incubation temperature on development rate, growth, survival and some physiological parameters during embryonic and larval development in Rainbow trout (Oncorhynchus mykiss)

Temperature is one of the most important environmental factors affecting of fish embryos and the survival and growth of fish larvae. In this study, eyed eggs of rainbow trout were incubated and reared until 30 day after first feeding at three constant temperatures including 7, 11 and 15 °C with four replicates in order to observe their survival, growth, rate of development and some physiological parameters. Triplicate pools of 5 embryos or larvae were taken at 7 different stages and then immediately deep-frozen in liquid nitrogen until analysis. Development rate was significantly different between temperatures. There was significant survival rate among the treatment groups (P < 0.05) at different stages, indicating different optimum temperature at different life stages. Survival at eyed stage to hatching stage at 7 and 11 ºC were significantly higher than 15 ºC. Survival at hatching to Swim up stage at 7 ºC were significantly higher than that of 11 and 15 ºC, but survival of swim up to 30 DAFF at 15 ºC were significantly higher than 7 and 11 ºC. Cumulative survival of 7 ºC was significantly higher than 11 and 15 ºC groups. Final weight was significantly higher at 15 ºC. So that mean weight at the end of experiment were 342.57, 596 and 1116.29 mg for 7, 11 and 15 ºC groups, respectively. A two-way analysis of variance showed that developmental stage and temperature had significant overall effects on total protein and total immunoglobulin, and there was a significant interaction among factors. In the case of albumin and Albumin/globulin ratio, Temperature had no main effect on albumin and Albumin/globulin ratio but stage showed a main. The interaction effect was significant too. In conclusion, although the egg incubated at 15 ºC had lower survival rate at early stages, but subsequent higher survival after emergence and faster growth may be an effective way to reduce larval mortality and better larviculture management.