| The study was conducted to two different size of GIFT strain of Nile tilapia Oreochromis niloticus, the effects of dietary available phosphorus levels and calcium/phosphorus ratios on growth performance, body composition, tissue phosphorus content and apparent digestibility in GIFT (46.03±2.14g), and the effects of dietary available phosphorus levels on growth performance, body composition and tissue phosphorus content in GIFT(184.46±8.13g), determining the optimal levels of available phosphorus and calcium/phosphorus in this two different size of fish, and providing theoretical foundation rational allocation for GIFT strain of Nile tilapia. The contents and results are as follows:1. A study was conducted to estimate the optimum requirement of dietary phosphorus for genetically improved farmed tilapia (GIFT) strain of Nile tilapia Oreochromis niloticus under indoor cultivation. Six purified diets were formulated to contain graded levels (0%(control diet),0.29%,0.48%,0.76%,0.91%, and1.09%) of available phosphorus from dietary ingredients and monocalcium phosphate. Each diet was randomly assigned to triplicate groups of36juvenile fish (initial body weight,46.03±2.14g). Fish were fed third daily (at8:30,12:30,16:40, respectively) to satiation for8weeks. The results showed that fish fed the three diets with low levels of phosphorus (0%,0.29%and0.48%) had significantly lower weight gain rate (WGR), specific growth rate (SGR), and feed efficiency (FE) than those fed the test diets with available phosphorus levels of0.76%and above (0.91%and1.09%)(P<0.05). The survival rate of fish fed the control diet was significantly lower than that the fish fed the other diets (P<0.05). Whole body viscerosomatic index (VSI) and crude lipid content decreased significant with the increase of the dietary available phosphorus levels (P<0.05), While the contents of crude ash, calcium, phosphorus in the whole body and vertebrae was opposite (P<0.05), and Ca/P ratios in whole body and vertebrae were not influenced by dietary phosphorus supplementation (P>0.05). The blood chemistry analysis showed that dietary available phosphorus had significant effects on serum phosphorus concentration, enzyme activities of alkaline phosphatase (ALP), parathyroid hormone (PTH) level, as well as contents of triacyglycerol (TG) and total cholesterol (T-CHO)(P<0.05). Dietary phosphorus had no significant effect on serum calcium concentration (P>0.05). Quadratic curve analysis based on SGR indicated that the minimum dietary requirement of available phosphorus for maintaining optimal growth of tilapia was0.81%. Based on the phosphorus content in either whole body or vertebrae, the dietary available phosphorus requirements were0.86%and0.82%, respectively.2. This experiment was to conducted to evaluate the effects dietary calcium/phosphorus ratios (mass ratio) on the growth performance, feed utilization efficiency, the apparent digestibility of phosphorus, body composition, inorganic matter content in bone and serum biochemical indexes of GIFT strain of Nile tilapia Oreochromis niloticus juvenile, to determine the optimal dietary calcium/phosphorus ratio of feed. GIFT strain of Nile tilapia Oreochromis niloticus (Initial weight (46.03±2.14) g) were satiably fed on six experimental isonitrogenous and isoenergetic purified diets with containing increasing contents of total phosphate (9-10g/kg) and calcium/phosphorus ratios (1.8:1,1.3:1,1:1.1,1:1.5,1:2.5and1:2.9) for8weeks respectively. Potassium dihydrogen phosphate was the source of phosphate and calcium chloride was the source of calcium. Each treatment was triplicate. The results showed that fish fed the diet with high level of calcium/phosphorus ratio (diet1) had significantly lower weight gain rate (WGR) and specific growth rate (SGR)than those fed the test diets with diet3, diet4, diet5, diet6(P <0.05), and there were no significant differences among treatments of diet3, diet4, diet5, diet6(P>0.05); the feed conversion ratio (FCR) of fish fed the test diets with diet5was significant lower than that the fish fed diets1(P<0.05), while the survival rate(SR), condition factor(FR), viscerosomatic index (VSI), hepatosomatic index (HSI) of fish were not significant differences among various dietary treatments(P>0.05). The body composition analysis showed that dietary calcium/phosphorus ratios had no significantly effect on crude protein and crude ash contents in the whole body, as well as vertebrae crude ash content(P>0.05). The whole body and vertebrae calcium, phosphorus concentration were significantly affected by dietary calcium/phosphorus ratios (P<0.05), as well as the muscle crude lipid and crude ash contents(P<0.05), while Ca/P ratios in whole body and vertebrae were not significant differences among various dietary treatments(P>0.05). The blood chemistry analysis showed that dietary calcium/phosphorus ratios had distinct effects on serum phosphorus concentration, enzyme activities of alkaline phosphatase (ALP) and parathyroid hormone (PTH) level, as well as contents of triacyglycerol (TG) and total cholesterol (T-CHO)(P<0.05), but serum calcium content was not clear influenced by dietary calcium/phosphorus ratios (P>0.05). Broken-line analysis based on SGR indicated that the optimum calcium/phosphorus ratios requirement for the optimal growth of GIFT tilapia was1:1.5. Based on the phosphorus concentration either in the whole body, vertebrae or serum, the dietary calcium/phosphorus ratios requirements were1:1.1,1:1.1and1:24, respectively. It can be concluded that the calcium/phosphorus requirement for GIFT strain of Nile tilapia Oreochromis niloticus juvenile is1:1.1-1:1.5.3. A study was conducted to estimate the optimum requirement of dietary phosphorus for genetically improved farmed tilapia (GIFT) strain of Nile tilapia Oreochromis niloticus under indoor cultivation. GIFT strain of Nile tilapia Oreochromis niloticus [initial weight (184.46±8.13)g] were satiably fed on six experimental isonitrogenous and isoenergetic purified diets with containing increasing contents of available phosphorus [0.15%(control diet).0.40%、0.66%、0.91%、1.17%and1.43%] for9weeks respectively. Monopotassium phosphates was a source of phosphorus. Each treatment was triplicate. The results showed that fish fed the two diets with available phosphorus levels of0.66%and0.91%had significantly higher weight gain rate (WGR) and specific growth rate (SGR) than those fed the other test diets(P<0.05), and the feed efficiency (FE) was significantly higher than control diet(P<0.05). The whole body viscerosomatic index (VSI), hepatosomatic index (HSI) and condition factor (CF) decreased significant with the increases of the dietary available phosphorus levels (P<0.05), while the survival rate (SR) of fish was not significant differences among various dietary treatments(P>0.05). The whole body crude protein, crude ash, and phosphorus concentration increased significantly with the increases of the dietary available phosphorus levels, as well as vertebrae and scale crude ash and phosphorus concentration(P<0.05), while the whole body crude lipid content decreased significant with the increases of the dietary available phosphorus levels (P>0.05). Quadratic curve analysis based on SGR indicated that the minimum available phosphorus requirement for the optimal growth of GIFT tilapia was0.81%. Based on the ash concentration in the vertebrae, the dietary available phosphorus requirement was1.23%. Based on the phosphorus concentration either in the whole body or scale vertebrae, the dietary available phosphorus requirements were0.82%,1.12%, respectively. |
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