This study was carried out to investigate the effect of protein levels and different regimes of polyethylene sheet cover on the growth performance of mono sex Oreochromis niloticus (1±0.02g). This study was begun at 1st October, 2013 and lasted at 15th September, 2014. An experiment was designed to test two dietary protein levels (25 or 32%) within each level two cover systems with polyethylene sheets as 75% or 100% pond area were also tested. The experimental period was divided into three periods, the first one before over-wintering (1st October 2013 to 31st November 2013). The second period of this experiment continued during the over-wintering (from 1st December 2013 until 15th April 2014). The third period continued after over-wintering (from 16th April 2014 until 15th September 2014). O. niloticus reared during the first and second periods of this experiment in concrete ponds, while at the beginning of third period O. niloticus was transferred to earthen ponds (4200 m2) at stocking rate of 12000 fish/pond for all treatments. O. niloticus was fed during this period on artificial feed containing 25% crude protein at feeding rate of 3% of total biomass and organic and inorganic fertilization were applied. The treatments applied were T1 (25% protein+75% covering area), T2 (25% protein+100% covering area), T3 (32% protein+75% covering area) and T4 (32% protein+100% covering area). Results obtained indicated that T4 showed that, the best growth performance, the highest biochemical parameters, and the highest protein, ash, fat content of fish bodies, while T1 recorded the highest liver function.
Based on results obtained in this study and on the economical evaluation, it can be concluded that feeding O. niloticus fry on diet containing 32% protein, before and during the winter season, taking into account the coverage of concrete ponds by polyethylene cover during the winter months, followed by feeding fish during the growing season on diet containing 25% crude protein has led to an increase in survival rate, increased the vitality of fish and increased the body weights at the end of the season.
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