الفهرس 
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Abstract
Tilapia species comprises a greater part of the Egyptian fish fauna that extensively inhabit the River Nile and its tributaries The Egyptian Government exerts a tremendous efforts to increase the fish production as an other cheap source of animal protein. Hence many fish aquaculture stations were constructed By regarding such concept ,therefore the present study has been planned as an attempt to high some light on the reproductive biology of Nile tilapia (0. nitoticus
The present investigation deals to some extent with the enhancement of the process of maturation of the studied fish .Therefore ,a combined fish treatment was applied at the same time .One of them is the principal abiotic environmental factor which is the temperature (25°C& 28°C).The second tested treatment is the pituitary extract or human chorionic gonadotropin (HCG)as a mean to induce the fish pituitary gland to rise the gonadotropin hormone ( Gt H) which enhance the growth of the gonads.
The first examined criterion in the present study is the distribution of different fish maturity stages under various experimental designs.lt was found that the rise of water temperature alone enhance the maturation process ,the water temperature level 28°C gave a more advanced maturity stages for both male ( Stage V 66.67 % ) after 30 days and female (Stage V 60%) after 20 days . By the combined fish treatment with pituitary extract and water temperature 28°C, the ripe male appeared after 20 days in a high percentage of appearance (75%) and the ripe female after 30 days in a 66.67% percentage of appearance. Concerning the effect of HCG, it is obvious that the HCG accelerates the maturity stages of male and female fish 83.33% appeared-in a ripe stage of both sexes on the 40 th day of fish group subjected to 25°C..
The gonadosomatic index (GSI) of male fish injected with pituitary extract or HCG was generally elevated. The maximal rise of GS1 value was noticed in case of fish group subjected to water temperature 28°C being above the control value by + 108.6592% on the 40 th day for pituitary extract and +332.6708% on the 20 th day for HCG. Similarly, the GSI of female fish was increased after the hormone treatment. In this case it is obvious that the HCG treatment gave a better results than the pituitary extract.
Considering the histological changes of fish gonads, the present study declare the success of the hormones and temperature treatments for induction of gonads ripeness.
By taking the changes of hepatosomatic index (HSI) into consideration ,it is obvious that the HSI values are reduced after the fish treatment with pituitary extract or with HCG . This reduced HSI value reveals a transfer of vitellogenin from the liver into the blood stream and finally to the gonads.
A sharp increase was recorded in the level of plasma testosterone in case of male and female tilapia fish injected with pituitary extract or HCG This result suggest a relationship between the sex steroid hormones and the ripening of fishes. The plasma estradiol level was generally reduced in case of male fish treated with pituitary extract .Whereas, those of HCG treated group was generally elevated .The most pronounced hormone rise being +142.1743% above the control value was attained in case of fish group reared at a water temperature 28 C for 40 days period.
A marked increased plasma estradiol level was recorded for female fishes injected -with pituitary extract or HCG .Stich increased hormone level are strictly correlated with the rise in GSI values , which may reflect active oogenesis.
Male and female 0. niloticus injected with pituitary extract or HCG have a higher plasma follicle stimulating hormone (FSH).Therefore, it can be concluded that the elevated level of FSH and high GSI values led to ovulation of the studied fish.
The liver aspartate aminotransfcrrase (ASAT) activity was generally reduced in case of male fish group treated with pituitary extract and subjected to water temperature 25°C. Whereas, those of male fishes subjected to water temperature 28°C was sharply elevated . Such elevated enzyme activity may reflect increased cortisol secretion by pituitary gland. HCG treated male and female tilapia fish have a general reduced liver AsAT activity which may reflect a degree of hepatic cell damage.
HCG or pituitary extract treatment induce a marked increased AsAT activity in the testis of male fish. Such elevated enzyme activity suggests active protein metapolism during the process of spermatogenesis.
In contrary , the HCG or pituitary extract treatment induce a
• general reduction of the ovary AsAT activity . The present study suggests to some extent that such reduced enzyme activity results mainly from reduced ovarian tissue and increased ova diameter, a phenomenon that occurred during ripeness.
The muscle AsAT enzyme activity was generally reduced in case of male fish treated with HCG or pituitary extract. In case of female fish, the pituitary extract injection induce a general reduced muscle AsAT activity whereas the HCG treatment increased its activity .
A marked reduction of plasma AsAT enzyme activity was noticed for male fish subjected to pituitary extract or HCG. The reverse is true for female tilapia fish subjected to both studied hormones where the plasma AsAT activity was generally increased.
Concerning the MAT enzyme activity it is obvious that the pituitary extract treatment induce a generally elevated AIAT activity in the liver of male and female fishes. HCG treated male and female fishes have a different changes in the liver MAT activity.
The testis AIAT activity was generally reduced in case of fish group treated with pituitary extract. Also, HCG treatment induce a reduced testicular enzyme activity in ease of fishes reared at a water temperature 25°C. Whereas it was increased markedly in case of fishes raised at 28°C temperature . Female O.niloticus injected with pituitary extract have a reduced ovary AIAT activity (At temperature 25°C) and increased enzyme activity (At temperature 28°C).
A generally elevated ovary AIAT activity was recorded for female fishes injected with HCG and subjected to water temperature 25°C. Whereas a drastic reduction of the enzyme activity was obtained in case of fish group raised in a water temperature 28°C.
The muscle AIAT activity was increased in male and female tilapia fishes injected with pituitary extract and subjected to water temperature 25°C. Whereas, in case of fish group reared in a water temperature- 28°C its activity was noticed to be elevated. Also, at the same water temperature level, HCG treatment induce an enhanced muscle MAT activity of both sexes of the studied fish.
Male and female aniloticus injected with pituitary extract
(Temperature 25°C) have a general reduced plasma AIAT activity. Whereas male fishes reared in warmer water exhibit a reduced enzyme activity.
The AIAT enzyme activity in the plasma of male fish treated with HCG was generally increased. Whereas those of female fishes were generally reduced.
The male and female fishes injected with pituitary extract have a generally elevated total protein in the liver. The HCG treated fishes have a fluctuating changes in the liver protein content. A marked increased total protein content in the testis and ovary was noticed in the male and female fishes injected with pituitary extract or HCG. The increased protein level in fish gonads coincide with the elevated GSI as the fishes reach ripeness.
Due to pituitary extract injection the muscle total protein content was increased in the male and female fishes subjected to water temperatures 25°C and 28°C.
Male a niloticus treated with HCG have a general elevated muscle total protein content. Whereas, in case of female fish it was generally reduced.
The plasma total protein content was increased in case of male and female fishes treated with pituitary extract or KG. Such elevated plasma protein level may be results from water influx from the blood to the tissues.