Studies On The Utilization Of Plant Protein Sources By Tilapia Oreochromis Niloticus×O.aureus And A Few Methods On Improving Its Utilization

Tilapia as an important food fish in developing countries is widely used in commercial farming systems for intensive aquaculture,and constitute the third largest group of farmed finfish,only after carps and salmonids,with an annual growth rate of about 11.5%.Currently, tilapia culture is widely practiced in many tropical and subtropical regions of the world, especinaly in China.More than 22 tilapia species are being cultured worldwide.However, hybrid tilapia Oreochromis niloticus×O.aureus is the most commercially cultured tilapia species in the South China,the culture scale has rapidly developed in the past few years.The shortage in world production of fish meal(the main conventional protein source) coupled with increased demand for fish meal in feeds for livestock and poultry is likely to reduce the dependence on fish meal as a single protein source in aquafeeds.Therefore,fish nutritionists have made several attempts to partially or totally replace fish meal with less expensive,locally available protein sources.But,the limiting factors in the utilization of plant protein sources by fish are related to diet palatability,digestibility and essential amino acid balance.Fish species, food habit and fish size also have effects on the utilization of plant protein sources by fish.The optimal dietary plant protein level usually to some degree varies by fish species and dietary protein level.It is very important aspects that how to improve the utilization of plant protein sources in aquafeeds.Therefore,specific strategies and techniques to increase the use of plant feedstuffs in aquafeeds and limit potentially adverse effects of bioactive compounds on farmed tilapia are discussed in this paper.The results can be briefly summarized as follows:1.This study evaluated the effects of four vegetable protein sources in the practical diet of hybrid tilapia on growth performance.Four isonitrogenous and isocaloric practical diets included only soybean meal(SBM),rapeseed meal(RSM),cottonseed meal(CSM) and peanut meal(PNM) as sole vegetable protein source with supplemental 14%fish meal(FM) were formulated.The results showed that the best performance in terms of final weight, specific growth rate(SGR),relative weight gain ratio(RWGR),feed conversion ratio(FCR) and protein efficiency ratio(PER) were shown in Diets SBM and CSM.The 5 parameters were significantly affected by Diet RSM(P＜0.05).Whole body moisture content in Diet PNM was significantly lower than that of other 3 groups(P＜0.05).The liver lipid content in Diet RSM was significantly higher than that of other 3 groups(P＜0.05).And viscera ratio, hepatosomatic index,condition factor and the liver glycogen contents were not significantly affected(P＜0.05).Protease activities of intestine in Diets SBM and CSM are significantly higher than that of other 2 groups(P＜0.05),and the lowest protease activities of intestine and hepatopancreas in Diet RSM.No significant differences were observed in amylase activities of intestine and hepatopancreas among 4 diet groups(P＞0.05),respectively.The highest activities of GPT,GOT and SOD in the liver were observed in Diet SBM and the poorest in Diet RSM.The results show that 36%SBM or 39%CSM may be included in the practical diets without inhibiting fish performance.The inclusion of 50%SBM resulted in significantly lower growth performance and feed utilization.2.This study evaluated the effects of replacing fish meal(FM) in the practical diet of hybrid tilapia with different soybean meal(SBM) levels on growth performance.Juvenile tilapia were fed either a mixture of FM and SBM based(control,Diet 1) diet or a soybean meal replacement isonitrogenous and isocaloric diet.The treatments(Diets 2-5) consisted replacing 25%,50%,75%and 100%FM protein with SBM protein,respectively.Relative weight gain ratio(RWGR),specific growth rate(SGR) and protein efficiency ratio(PER) were significantly reduced as the proportion of soybean meal in the diets increased.The best performance in SGR,RWGR,feed conversion ratio(FCR) and PER were acquired in 16%FM (Diet 1) and 12%FM(Diet 2) group.It was found that these four ratios were affected significantly by no fish meal diet(Diet 5)(P＜0.05).Whole body moisture content increased significantly(P＜0.05),and protein content decreased with increasing dietary soybean meal levels.The viscera ratio,hepatosomatic index,condition factor,the liver lipid were not significantly affected by dietary treatments(P＜0.05).Activities of protease,amylase and lipase in stomach,intestine and hepatopancreas of hybrid tilapia significantly decreased (P＜0.05) with increasing dietary soybean meal levels,respectively.GPT and GOT activities of the juvenile tilapia liver in no fish meal treatment are significantly lower than that of other 4 groups(P＜0.05).The results show that in practical diets,FM can be replaced in terms of protein by 25%soybean meal protein without inhibiting fish performance.The inclusion of 100%protein from plant protein sources resulted in significantly lower growth performance and feed utilization.3.This study evaluates the effect using less-expensive RSM-CSM combo feed mixed with formally used soybean meal(SBM) for juvenile tilapia in different combinations.Four Soybean-based(the control,Diet 1) and RSM-CSM Combo(RSM:CSM = 1:2) were tested at equal nitrogen and caloric basis.The combinations include the replacement of SBM at 6% (Diet 2),12%(Diet 3) and 18%(Diet 4) with the combo,respectively.The results showed that the best performance in terms of specific growth rate(SGR),relative weight gain ratio (RWGR),feed conversion ratio(FCR) and protein efficiency ratio(PER) were shown by the Diets 3 and 4.The 4 parameters were affected significantly by soybean-free diet(P＜0.05).No significant differences were observed in dry matter,whole body moisture,protein,lipid and ash among 4 diet groups(P＞0.05).Viscera ratio,hepatosomatic index and the liver lipid content did not change significantly(P＜0.05).GPT and GOT activities of the tilapia serum in no-soybean meal treatment are significantly higher than that of other 3 groups(P＜0.05). However,SOD and LZ activities in no-soybean meal groups are significantly lower than that of the other groups(P＜0.05).The results show that RSM-CSM combo may be included in the diet up to 52%as a substitute for SBM.4.Five practical diets were formulated to contain five levels of methionine 0.45%,0.50 %,0.55%,0.60%,0.65%(containing cystine 0.52%) respectively.Results indicated that the practical diets containing free methionine improved the specific growth rate(SGR),feed conversion ratio(FCR),apparent protein retention(APR) and hepatopancreas lipid content in comparison with the basal diet(P＜0.05).Significantly higher the concentration of serum free methionine was observed in juvenile hybrid tilapia fed diet with methionine 0.50%level than those of fish fed with other diets(P＜0.05).But body protein and body amino acids contents of tilapia was not significantly difference among the five groups(P＞0.05).Supplementation of free methionine was proved to be a significantly better way for improving protein utilization in plant proteins based diets of tilapia5.A commercial enzyme complex(containing neutral protease,Beta-glucanase and xylanase) was included at the level of 0.0(control group),1.0 and 1.5g kg^-1 diet to formulate three test diets.The results showed that specific growth rate(SGR) and feed efficiency ratio (FER) significantly increased(P＜0.05) with increasing dietary enzyme levels.The highest feed intake(FI) was recorded in the group fed the control diet(P＜0.05).The highest apparent protein retention(APR) was observed in fish fed the diet containing 1.5g kg^-1 diet(P＜0.05). No significant differences were observed in the apparent digestibilities(ADC) of protein,lipid and gross energy among dietary treatments(P＞0.05).However,the ADC of dry matter(DM) in fish fed high supplementation(1.5g kg^-1) was significantly higher than the control and low supplementation(P＜0.05).There were no significant differences in condition factor,whole body moisture,protein,lipid and ash among dietary treatments.Viscera ratio,hepatosomatic index and the liver lipid decreased significantly with increasing enzyme(P＜0.05).Both protease and amylase activities in the intestine and hepatopancreas of juvenile hybrid tilapia significantly increased(P＜0.05) with increasing dietary enzyme levels.The results suggested that enzyme supplementation can significantly improve growth performance and feed utilization in juvenile hybrid tilapia.6.Five practical diets were formulated to contain 2 levels of lipid and 3 levels of LH-3 (LH-3 contents in diets were 0.0%,0.05%and 0.1%) on the basis of isonitrogen.The results showed that the best performance in specific growth rate(SGR),feed conversion ratio(FCR) and protein efficiency ratio(PER) were acquired in 0.05%and 0.1%LH-3 groups.It was found that the above three ratios were affected significantly by no LH-3 diet(P＜0.05).No significant differences were observed in dry matter,whole body moisture,protein,lipid and ash among treatments(P＞0.05).There were no significant differences in viscera ratio and hepatosomatic index among dietary tretaments(P＜0.05).The liver lipid contents decreased significantly as LH-3 level increased in diets.GPT and GOT activities of the juvenile tilapia liver are significantly higher than that of the other groups(P＜0.05) as LH-3 level increased in diets. However,SOD activities of the juvenile tilapia liver in 0.1%LH-3 groups are significantly higher than that of the other groups(P＜0.05).In conclusion,it is likely that a combination of plant-derived feed ingredients can effectively replace fish meal,and that supplements,such as amino acids,LH-3 and exogenous enzymes,will be needed to produce aquafeeds without fish meal that improve growth rates necessary for the economic production of farmed tilapia.