الفهرس 
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Abstract
The results in this study could be summarized as follows
1 — In Tilapia nilotica, the breeding season under natural laboratory condition extended from May till October. The maximum spawning frequency reached during July and August at average water temperature of 28C, then decreased gradually during September and October and stopped
completely from November till April where the water temperature was less than 24C.
2-It has been found that there was a direct relationship between water temperature and spawning frequency.
3-There was an inverse relationship between water temperature and incubation period, rearing period and the inter spawning interval.
4-There was a direct relationship between the female body weight and the number of fry produced.
5-Better growth was achieved in the fish group reared in water temperature 27 + 1 C° while stunted growth was observed in the fish group reared in an average water temperature of 15.6 C°.
6-Reduced water temperature has an injurious effect on the viability of Tilapia .100% mortality was recorded at water temperature less than 16C’
during the first two months after fry releasing. In the control group, which was reared at water temperature of 27 + IC , the mortality ?/10 was greatly
diminished and no mortality was observed at the age of two months and onward.
7-The gonadosomatic index (G-SI). the oocvte and the seminiferous tubules diameter were diminished significantly in both sexes reared in
average water temperature of 16.5C as compared to those reared in water
temperature of 27 ±
8- There was a direct relationship between the age at sexual maturity and the stocking density while there was an inverse relationship between the body weight at sexual maturity and the stocking density. Within the same stocking density per aquarium, it has been found that males attained higher body weights and reached sexual maturity earlier than females.
9- It has been found that there was a direct relationship between the body weight of males and the spawning pit size, while there was an inverse relationship between the body weight of the male and the time elapsed from stocking until nest building is completed. All males preferred to build their
nests in the region of sand.
10- There was a direct relationship between methyltestosterone (MT) (dose & duration) and the percentage of males obtained. Administration of (MT) at doses of 30 & 60 malkg feed for 28 days resulted in 100 % males.
11-All hormone treated groups had a significantly higher body weight than the control group and there was also a direct relationship between the final body weight and the dose and duration of methyltestosterone treatment.
12-It has been found that the survival rate in the hormone treated groups
was nearly the same as in the control group.
13-Increasing the age difference between the stocked individuals resulted in an ascending increase in the percentage of cannibalism by the older individuals. So that the percentage of cannibalism decreased gradually as
the differences between age decreased.
14- There was a direct relationship bemeen the body weight of shooter and the percentage of fry cannibalism. When the shooter individual was removed from the control group at the time of its appearance, no fry losses was observed.
15-Tilapia nilotica fry and fingerlings fed only on the powdered feed
at the water surface, the suspended powder and the powder at the bottom of the aquarium but did not fed on the pellets of 0.5 cm and 1 cm lengths.
16-In Tilapia nilotica the larger body weight male or female dominated other individuals in the aquarium. So that the body weight is crucial in detei mining dominance.
17-In both sexes of Tialpia nilotica when the resident individuals were the larger ones they won all contests. The time of the contests was shorter when the winner was the larger residents (male or female) while the time was prolonged in both sexes when the resident was the smaller individual and was longer when the larger intruders won.