Effects Of Circled Feeding Regimes, Dietary Protein And Lipid Levels On The Growth Of Tilapia(Oreochromis Niloticus)

In this study, the effect of the different feeding regimes on the gowth performance of tilapiawas investigated using seven isonitrogenous (33%crude protein) and isolipidic (8%crude lipid)experimental diets, through which the best feeding regime was seleted. Under the optimalfeeding patern, another trial was conducted to evaluate the effects of different protein (30%and36%) and fat (5%and11%) levels in diets on the growth performance of tilapia. The results arepresented as follows:1. Effect of circled feeding regimes on feeding, growth performance and biochemicalindexes of tilapiaSeven different cycled feeding regimes that were subjected to alternately fasting days andsubsequent refeeding, were designed as follows: S0(control, fed daily) and other six groups ofS1F3, S1F5, S1F7, S2F3, S2F5and S2F7. The trial lasted for43days. The SGR of all treatedgroups were significantly higher than that of control group (P<0.05). The values for SGR ingroups S2F3(7.00%) and S1F3(6.62%) were significantly higher than than those of othergroups(P<0.05), and the former was higher in SGR than the latter (P<0.05); The WGR values ofS1F3(788.1%), S1F5(781.8%), S1F7(794.8%) were not different from the value of S0group(P>0.05), but those in groups S2F3(562.8%), S2F5(585.0%) and S2F7(715.7%) weresignificantly lower than that of the control group (P <0.05), and the value of group S2F3was thelowest across treatments. For the regimes of1-d starvation and subsequent refeeding (S1F3,S1F5and S1F7), the tilapia abtained completely compensatory growth, but for other circledfeeding regimes (S2F3, S2F5and S2F7), the fish only had partial compensatory growth. Feedingregimes obviously affected whole-body composition of tilapia. For the regimes of1-d starvationand subsequent refeeding (S1F3, S1F5and S1F7), body protein and ash contents increased, butmoisture content decreased with increasing the feed-ration days. For the regimes of2-dstarvation and subsequent refeeding (S2F3, S2F5and S2F7), body protein and lipid contentsincreased, but moisture content decreased with increasing the feed-ration days. The RNA/DNAratio in group S2F3was lower than that in group S1F7, but no differences between other treatedgroups were observed. There was no difference in serum GPT activity between S1F3, S1F5andS1F7. However, for the regimes of2-day starvation and subsequent feeding (S1F3, S1F5andS1F7), serum GPT activity decreased with the increase in feed-ration days. The TG content inserum of group S1F3was higher than those in the rest groups. The CHO content in S1F5group was significantly higher than the control group. Serum HDL-C contents in S1F5and S1F7groups were higher than that of the control. For the regimes of2-day starvation and subsequentfeeding (S2F3, S2F5and S2F7), CHO and HDL-C contents increased with the increase infeed-ration days. The results indicate that the completely compensatory growth of tilapia couldbe attributed to both promoted SGR and feed intake. The optimal feeding regime is SIF3fortilapia under the present experimental conditions.2. Effects of dietary different protein and fat levels on the growth performance andbiochemical indexes of tilapia under the same feeding regimeThe S1F3was selected as the feeding pattern, and under the pattern a feeding trial wascarried out to investigate the effects of different dietary protein and lipid levels on growthperformance of tilapia. A reference diet and four experimental diets were formaluated: referencediet (33%protein and8%lipid), D1(30%protein and5%lipid), D2(30%protein and11%lipid), D3(36%protein and5%lipid) and D4(36%protein and11%lipid). The trila includednine feeding groups: S1F3(P30F5), S1F3(P30F11), S1F3(P36F5), S1F3(P36F11), S0(P30F5),S0(P30F11), S0(P36F5), S0(P36F11), and reference diet group: S1F3(P33F8). The trial lastedfor44days. Although WGR (847.2%) in S0(P36F11) was highest across treatments, and thevalue was higher than the values in S1F3(P33F8), S1F3(P30F5), S1F3(P30F11), S1F3(P36F5),S1F3(P36F11), and S0(P30F5), but was not different from those of S0(P30F11) and S0(P36F5). The value for WGR in S1F3(P30F5) was the lowest, but was similar to the values ofS1F3(P30F5) and S1F3(P30F11). Feeding reference diet had the highest SGR (6.5%) amongtreatments, and the value was similar to that of S1F3(P36F5), but was higher than those of othergroups. The results indicate that the feed high in protein or low in lipid could not help improvingfeed efficiency. Under the same normal feeding pattern, dietary high protein level promotedWGR, SGR, FCE and CHO content, but reduced PER; dietary high lipid level improved WGR,SGR, FCE and VSI, but decreased PER; both dietary protein and lipid levels did not affect GOTactivity, but improved GPT activity. Under the same circled feeding pattern, the diet high inprotein improved FCE but decreased VSI and PER; the high lipid diet improved FCE. Bothdietary protein and lipid levels significantly raised the RNA/DNA ratio in muscle regardless ofeither normal or circled feeding regimes. Based upon the above results, the diet containing30%protein and11%lipid is superior to fish growth performance under the S1F3pattern in thepresent study.