Effect of salinity and protein levels on haematological, and physiological changes and growth of hybrid tilapia (Oreochromis mossambicus × Oreochromis niloticus)

The experiment was conducted to determine the effect of salinity and dietary protein levels on  physiological and haematological changes as well as growth of the juveniles of hybrid tilapia (Oreochromis mossambicus×Oreochromis niloticus). Fish were stocked at ۲۰ fish ۵۰L-۱. The initial average weight of the juveniles was ۲.۱±۰.۰۲ g and they were kept in salinities ۰, ۱۰, ۲۰ and ۳۵ ppt (S۱, S۲, S۳ and S۴, respectively) and fed with ۳۰% (P۱) and ۴۰% (P۲) dietary protein levels for ۴۵ days. The harvesting weight and SGR were not significantly (p>۰.۰۵) different between S۲ and S۳ treatments for ۳۰% to ۴۰% protein levels varied in connecting S۲-S۳ with P۱diets or in between S۲-S۳ with P۲ diets. The food consumption significantly (p<۰.۰۵) increased with decreasing protein levels (۴۰% to ۳۰%) in diets at ۱۰-۲۰ ppt salinities. The survival rates were not significantly (p>۰.۰۵) different between ۱۰-۲۰ ppt salinities with P۱ and P۲ diets. The lowest FCR and highest muscular hydration were achieved at intermediate salinities with low protein diets. No obvious changes occurred in Hct%, Hb, plasma protein, muscles and liver protein levels in all treatments. Furthermore, the plasma cortisol and glucose levels tended to increase at higher salinities but were not significantly (p>۰.۰۵) different among all treatments. The physico-chemical parameters of water (i.e. dissolved oxygen: DO, temperature, ammonia etc.) were at a normal range throughout the study. Results showed that environmental salinity (۰-۳۵ ppt) had no adverse effects on growth and biochemical changes and also no required high protein levels in diets at any salinity.

Keywords:

Hybrid tilapia , Haematology , Physiology , Cortisol , Muscular hydration