Effects Of Different Dietary Starch, Protein And Lipid Levels On The Growth And Physiological And Biochemical Responses Of Nile Tilapia (Oreochromis Niloticus)

This study was conducted to determine the effects of different dietary starch level andprotein or lipid levels on growth and physiological and biochemical parameters of Nile tilapia(Oreochromis niloticus). The interaction between starch level and protein or lipid level and itsprotein-sparing and lipid-sparing effects of fat on growth performance were investigated. Theresults are presented as follows:1. Effects of different dietary starch and protein levels on the growth and biochemicalindicators of Nile tilapia.A3×2factorial design was used to determine the effects of dietary starch and proteinlevels in experimental diets on growth and physiological and biochemical indicators of Niletilapia. Six diets were formulated to contain different protein (24%,36%) and starch (0%,20%,40%) levels, i.e. D1(P24S0), D2(P24S20), D3(P24S40), D4(P36S0), D5(P36S20), and D6(P36S40). The tilapia juveniles with an initial average body weight of10.29±0.01g wererandomly assigned into six groups with triplicate tanks (twenty fish per tank). The fish in eachgroup were fed one of the diets to satiation twice daily for42days. The result showed thatdifferent dietary levels of protein and starch significantly affected WGR, SGR, FCR, PER andwhole-body composition in tilapia (P<0.05). In each dietary protein level, WGR, SGR, PER andthe whole-body crude protein and lipid contents increased with increasing level of dietary starch(P<0.05), but FCR showed the opposite trend (P<0.05), and there were significant differencesbetween non-starch treated group and starch-fed groups (P<0.05). In each dietary starch level,FCR and PER decreased significantly as the dietary protein level increased (P<0.05). There wasno interaction between dietary protein and starch levels on growth performance in tilapia, exceptfor whole-body composition. Starch in the diet showed a significant protein-sparing effect. Theresults indicate that appropriate dietary level of starch is beneficial to the growth of tilapia.The contents of plasma TG, T-CHO, plasma glucose, liver lipid, liver glycogen and muscleglycogen were all significantly affected by both dietary starch and protein levels (P<0.05). Thecontents of TG, T-CHO, plasma glucose and liver lipid increased with increasing levels ofdietary starch, but there were significant differences between non-starch treated group andstarch fed groups (P<0.05). Plasma GK activity increased with increasing dietary starch levels(P<0.05). In24%dietary protein level G-6-P and PEPCK activities decreased gradually with increasing dietary starch levels (P<0.05). The G-6-PD activity in P36S40was significantlyhigher than those in other treated groups (P<0.05), and and the ME activity in P36S20andP36S40was significantly higher than those of other treated groups (P<0.05). Plasma FASactivity increased slightly with increasing dietary starch level. The LPL activity incarbohydrate-fed groups was significantly higher than in non-starch treated groups (P<0.05).Plasma GPT and GOT activities increased with the increase in dietary starch and protein levels(P<0.05), but the activity of GLDH was significantly decreased (P<0.05). The plasma levels ofINS, IGF-1, CH and COR increased with the increase in dietary starch and protein levels. Therewas no significant differences in GC concentration among all dietary treatments (P>0.05). Theconcentrations of T3and T4in the starch-fed groups had significantly higher than the non-starchtreated groups (P<0.05). The results indicate that tilapia can effectively maintain plasma glucosebalance and the stability of internal environment through physiological and metabolic regulation,after feeding feed the rich-starch.2. Effects of different dietary starch and lipid levels on the growth and physiological andbiochemical indicators of Nile tilapia.A3×2factorial design was used to determine the effects of dietary starch and lipid levelsin practical diets on growth and physiological and biochemical indicators of Nile tilapia. Sixdiets were formulated to contain different lipid (5%,10%) and starch (0%,20%,40%) levels, i.e.D1(L5S0), D2(L5S20), D3(L5S40), D4(L10S0), D5(L1020), and D6(L10S40). The tilapiajuveniles with an initial average body weight of11.98±0.01g were randomly assigned into6groups with triplicate tanks (twenty fish per tank). The fish in each group were fed one of thediets to satiation twice daily for42days. The result showed that different dietary levels of starchand lipid significantly influenced WGR, SGR, FCR, PER and whole-body moisture and crude fatcontent in tilapia (P<0.05). In each dietary lipid level, WGR, SGR, PER, HSI and thewhole-body crude lipid content increased with increasing level of dietary starch (P<0.05), FCRshowed the opposite trend (P<0.05), and there were significant differences between non-starchtreated groups and starch-fed groups (P<0.05). In each dietary starch level, the dietary proteinlevel did not affect WGR, SGR, PER and FCR. There was no interaction between dietary lipidand starch levels on growth performance and whole-body composition in tilapia (P>0.05). Theresults indicate that lipid level in the diet decreases when dietary starch level increases. Thedietary starch has a significant lipid-sparing effect.Plasma contents of TG, T-CHO, glucose, liver lipid, liver glycogen and muscle glycogenwere all significantly affected by both dietary starch and lipid levels (P<0.05). TG content wassignificantly affected by both dietary starch and protein levels (P<0.05). The contents of T-CHO,plasma glucose, liver lipid, liver glycogen and muscle glycogen in starch-fed groups were significantly higher than that in non-starch treated group. The plasma GK, PK, G-6-PD and MEactivities increased gradually with increasing dietary starch and lipid levels (P<0.05), however,the activity of PEPCK and G-6-P was significantly decreased (P<0.05). The activity of FAS andLPL in starch-fed groups was significantly higher than that of non-starch treated group. PlasmaGPT and GOT activities significantly increased as dietary starch and protein levels increased(P<0.05), but the activity of GLDH significantly decreased (P<0.05). The plasma levels of INS,IGF-1, CH and COR increased with the increase in dietary starch and lipid levels (P<0.05). In5%dietary lipid level, GC level was not affected by starch level (P>0.05). The GC level inL10S40was ignificantly lower than that in fish fed with other diets (P<0.05). The concentrationsof T3and T4in the starch-fed groups were significantly higher than that in the non-starch treatedgroups (P<0.05). The results indicate that tilapia can effectively use of dietary starch and lipidthrough the glycometabolism and fat metabolism, then reduc protein catabolism.