JKAU: Mar. Sci., Vol. 22, No. 1, pp: 15-29 (2011 A.D. / 1432 A.H.) DOI : 10.4197/Mar. 22-1.2 15 Effect of Reducing Water Salinity on Survival, Growth Performance, Chemical Composition and Nutrients Gain of Gilthead Sea Bream Sparus aurata larvae. Mabrouk, H.A and Nour, A.M. 1 halone52@yahoo.com National Instit. of Ocean. And Fish., 21111, El-Anfoushy, Alex., Egypt. 1. Animal and Fish Production Dept., Faculty of Agriculture, Alexandria University (Al-Shatby) Abstract. The present study was conducted to investigate the effect of daily decreasing rate (DDR‰) of water salinity, from saline (32‰) to fresh water (.045‰), sudden or gradually, on survival percentage; growth performance; chemical composition and body nutrients gain of Gilthead Sea bream (Sparus aurata) larvae with an average weight 0.069 g) in acclimation trial for 32 days. Eight daily dilution rates were investigated,: 1, 2, 3, 4, 8, 16, 24 and 32 part per thousand (‰) in triplicate treatments. Natural food composed of Brachionus plicatilis and Artemia salina nauplii were introduced, through feeding sequence, twice daily at 8.0 a.m. and 14.0 p.m. during the experimental period. The results showed that survival, average daily gain. (ADG) (mg/fish/day), specific growth rate (SGR) (%d -1 ), protein, fat and energy gain increased with decreasing the daily dilution rate (DDR‰) of water salinity significantly (P<0.05) for all treatments except those subjected to 24‰ and 32‰ DDR. On the other hand, growth in weight was decreased from 1173.9% to 897.1% significantly (P<.0.5) with increasing DDR‰ from 1‰ up to 32‰0 Also, chemical composition for the experimental larvae was significantly (P<0.05) affected, where DM%, CP%, EE% and EC were increased with decreasing daily dilution rate of water salinity, while ash content decreased. It could be concluded that Sparus aurata larvae could be acclimatized to fresh water throughout gradual dilution system, and can grow well up to .045‰, under indoor hatchery conditions.