الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 186 |  |  |
| | | from | 186 | | |
Abstract
A field study was conducted on brood stock Nile tilapia to increase the propagation. Both sexes were individually stocked into Habas (enclosures) in an earthen pond and fed for 19 days on a basal diet supplemented with different additives at graded levels of each (0.5, 1.0 and 2.0 g Therigon®; 1.0, 2.0, and 3.0 g Nuvisol Hatch P®; 20, 40 and 60 mg Gibberllic acid and 700, 900 and 1100 mg L - carnitine / Kg diet). The obtained results were evaluated and the best treatment for each sex was chosen for mating. Results indicated that all pretreatments for males and females brood stocks of Nile tilapia positively affected the total count of the offspring produced. Yet, the Haba, in which the females were pretreated with 0.5 g Therigon® / Kg diet and the males pretreated with 700 mg L – carnitine / Kg diet, gave the highest total count of the offspring comparing with the other Habas. But, because of the high feed cost due to the additives cost, 0.5 g Therigon® / kg diet as pretreatment for ♀ only (3rd Haba), 2 g Nuvisol Hatch P® / Kg diet as pretreatment for ♀ only (5th Haba), followed by 0.5 g Therigon® and 700 mg L - carnitine / Kg diet for ♀ and ♂, respectively (4th Haba), respectively were the best economically. Also, anatomical and histological examinations of fish gonads showed that development and maturation of these gonads, as well as these feed additives led to reduced the microbial load (pathogenic bacteria and fungi) in treated fish organs by using the feed additives especially with low levels. So, It could be recommended to use such commercial feed additives for improving reproductive performance of Nile tilapia brood stocks to offer enough seeds for fish farms. It is recommend also to make other trials on different other additives at economical levels.