الفهرس 
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Abstract
Three experiments were carried out to study (1) The effect of different photoperiod regimes 24L:0D , 18L:6D , 12L: 12D as control & 6L: 18D using eight fiberglass tanks ‘’ 110 × 60 × 50 cm’’ with capacity of 240L water , (2) The effect of different background colours ( white, red, green, blue and black) using ten cylinder plastic tanks with capacity of 90L water on growth performance, survival rate, skin colour and proximate body composition of tilapia (O. niloticus) fingerlings averaging 15.2 g fed with diet containing 26.58 % protein. Different growth measurements of tilapia were recorded every 15 days intervals. The physico-chemical analysis of water were recorded daily. The body composition and skin colour of the whole fish were determined at the beginning and at the end of each experiment. (3) The effect of different water depths 75, 125 and 175 cm in cold season using twelve standing cages (100×200 ×200 cm) on survival rate and growth performance of tilapia (O. niloticus) fingerlings average weight 18 gm and adults average weight 100 gm . Transparency of water and mortality were recorded every 15 days, at the end of the experimental period, the fish were harvested, counted and the growth measurements ( weight and total length) were determined .
The results of the study showed that the 175 cm water depth was more suitable for the growth and survival % of tilapia (O. niloticus) fingerlings cultured during the cool season in Egypt. Also, photoperiod 24L: 0D and white tanks were more suitable for optimum growth performance, survival rate and skin colour of tilapia (O. niloticus) fingerlings than any other photoperiods or tank colour. Therefore, it could be recommended for carrying out these results under the similar experimental conditionsbr>Key words: Nile tilapioticus), photoperiod, background colour, water depth, skin colour, survival rate, growth performance.