الفهرس 
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Abstract
This study was carried out at Center Laboratory for Aquaculture Research, Abbassa, During six months from April till September 2016. This study was designed to investigate the effect of environmental stress on reproductive performance of teleost fish, A total number of 486 healthy Nile tilapia fish (Oreochromis niloticus) brooders included 324 females and 162 males with an average body weight of 120.8 and 128.3 g and body length 20.1 and 22.1 cm, of females and males, respectively. group (1) and (2): each contain 27 hapa were used in irrigation and well water fish farms. at spawning season all fishes were randomly distributed according to three different time periods TP1, TP2 and TP3 (24, 28 and 34 C°) respectively. Each treatment included nine hapas, each treatment was in triplicate stocking density were of SD1, SD2 and SD3 (2fish/ m2, 3fish/ m2 and 4fish/m2), respectively. Fecundity and egg diameter were decreased in (TP2) and with high stocking density (SD3). The best number of fries were observed at TP3 and SD2. The best values of survival rate were at TP3 and SD1. Serum glucose increased with the increasing of cortisol. A positive correlation was noticed (r= 0.9364) between cortisol and glucose and a negative correlation (r= -0.7328 and r= -0.7723) between cortisol and both testosterone and estradiol respectively. We concluded that using well water in fish farms at TP3 (28°C) with stocking density (SD2) 3/m³ is the optimum treatment for reproduction in tilapia. Slight increase in cortisol and in glucose levels occurred in O.niloticus subjected to temperature and stoking density indicate that this species is responsive to stress.