الفهرس 
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Abstract
This research aims to study the adaptation availability of two types of tilapia ( Nile tilapia, Red tilapia), and study the effect of different levels of salinity on growth performance, feed efficiency, body fish content, survival rates, and physiological changes resulting from fish farming in different levels of salinity related to osmoregulation.
The experiment was conducted using 90 fish for each type of tilapia and divided equally on 18 concrete ponds dimensions (80× 80× 70 cm) at density rate 10 fish per pond, using three levels of water salinity (fresh water 1-1.5 ppt – brackish water 17 ppt – saline water 28 ppt), and fish were fed with diet containing 32% protein, and feed allowance was 4% of fish body weight.
The results showed that Red tilapia was better than of Nile tilapia in growth performance, feed efficiency, and survival rate in different level of salinity. The increase in salinity reduced growth performance, feed efficiency, and survival rates of Nile tilapia. While saline water increases the body content of protein and ash and reduced the body content of fat for both of Nile tilapia and Red tilapia. The physiological changes of fish in saline water increasing Haemoglubin, Haematocrite, Total protein, Sodium, Potassium, and Cortisol were increased for both. Glucose levels were significantly higher in Red tilapia than in Nile tilapia.
Key words: Osmoregulation – Nile tilapia – Red tilapia – Physiological parameters.