Study On Suitable Protein/lipid Ratio In Feed In Three Growth Stages Of Cynoglossus Semilaevis

In this paper,three tests were performed to study dietary protein/lipid ratio on growth and biochemical parameters in tongue sole Cynoglossus semilaevis of three growth stages(initial body weight were about 50 g,150 g,and 400 g,respectively)under recirculating aquaculture system.Dietary protein/lipid ratio on muscle quality of 400 g body weight tongue sole was also evaluated.These results could provide references for feed formula design of tongue sole cultured in recirculating aquaculture system.Test 1: In order to find optimum dietary protein/lipid ratio for small-sized tongue sole,a 2×3 two-factor test was adopted to study dietary protein(53%,56%)and lipid(9%,12%,15%)on growth,biochemical parameters of test fish with initial body weight of 53.43 ±4.07 g.After 59 days of feeding,no significant difference of weight gain rate(WG),feed conversion ratio(FCR)and specific growth rate(SGR)were observed among test groups(P>0.05).Dietary lipid levels affected specific growth rate(SGR),protein efficiency ratio(PER),protein retention rate(PRR),and lipid retention rate(LRR)significantly(P<0.05).Specific growth rate(SGR),protein efficiency ratio(PER),protein retention rate(PRR),and lipid retention rate(LRR)decreased first and then increased with the increase of dietary lipid.The maximum specific growth rate(SGR),protein efficiency ratio(PER),protein retention rate(PRR),and lipid retention rate(LRR)were observed in 9% lipid group.Dietary lipid levels affected hepato somatic index(HIS)significantly(P<0.05).Hepato somatic index(HIS)increased first and then decreased with the increase of dietary lipid.The maximum hepato somatic index(HIS)was observed in 12% lipid group.No significant difference of condition factor(CF)and visceral body ratio(VSI)were observed among test groups(P>0.05).No significant difference of fish crude protein,crude lipid,moisture,ash were observed among test groups(P>0.05).The maximum NBT-positive cells was observed in group P56/L9(P<0.05).NBT-positive cells increased with the increase of dietary lipid.The maximum liver CAT activity was observed in group P56/L9(P<0.05).Dietary lipid levels affected liver T-SOD activity significantly(P<0.05).Liver T-SOD activity decreased with the increase of dietary lipid.The maximum liver T-SOD activity was observed in 9%lipid group.The maximum liver LZM activity was observed in group P56/L9(P<0.05).Dietary lipid levels affected liver LZM activity significantly(P<0.05).Liver LZM activity decreased with the increase of dietary lipid.The maximum liver LZM activity was observed in 9% lipid group.The maximum liver GOT activity was observed in group P56/L15(P<0.05).Dietary lipid levels affected liver GOT activity significantly(P<0.05).Liver GOT activity increased with the increase of dietary lipid.The maximum liver GOT activity was observed in 15% lipid The maximum muscle T-SOD activity was observed in group P56/L15(P<0.05).The maximum intestinal tract protease activity was observed in group P53/L9(P<0.05).No significant difference of amylase,lipase activity in the intestinal tract of fish were observed among test groups(P>0.05).In summary,for about 50 g of fish,the suitable protein / lipid ratio in dietary was 53% / 9%.Test 2: In order to find optimum dietary protein/lipid ratio for medium-sized tongue sole,a 3×2 two-factor test was adopted to study dietary protein(50%,53%,56%)and lipid(12%,15%)on growth,biochemical parameters of test fish with initial body weight of152.05 ± 3.70 g.After 58 days of feeding,the P56/L12 group demonstrated the best growth performance in terms of weight gain rate(WG),feed conversion ratio(FCR),and specific growth rate(SGR).Dietary protein/lipid ratio exerted significant interaction effect on weight gain rate(WG),feed conversion ratio(FCR),specific growth rate(SGR),protein efficiency ratio(PER),and protein retention rate(PRR)(P<0.05).The maximum protein retention rate(PRR)and lipid retention rate(LRR)were observed in group P56/L12(P<0.05).No significant difference of condition factor(CF)and visceral body ratio(VSI)were observed among test groups(P>0.05).The minimum hepato somatic index(HIS)was observed in group P56/L12(P<0.05).Dietary protein/lipid ratio exerted significant interaction effect on fish crude protein(P<0.05).The maximum fish crude protein was observed in group P56/L12(P<0.05).Liver GOT activity increased with the increase of dietary protein.The maximum GOT activity was observed in 56% protein group.The maximum muscle T-SOD activity was observed in group P50/L12(P<0.05).Muscle MDA content decreased with the increase of dietary protein.The minimum MDA content was56% protein group.No significant difference of amylase,protease,lipase activity in the intestinal tract of fish were observed among test groups(P>0.05).In summary,for about150 g of fish,the suitable protein / lipid ratio in dietary was 56% / 12%.In summary,for about 400 g of fish,the suitable protein / lipid ratio in dietary was 50% /15%.Test 3: In order to find optimum dietary protein/lipid ratio for large-sized tongue sole,a2×3 two-factor test was adopted to study dietary protein(47%,50%)and lipid(12%,15%,18%)on growth,biochemical parameters and muscle quality of test fish with initial body weight of 404.56 ± 4.09 g.After 60 days of feeding,the P50/L15 group demonstrated the best growth performance in terms of weight gain rate(WG),feed conversion ratio(FCR),and specific growth rate(SGR).Dietary protein and lipid levels affected protein retention rate(PRR)significantly(P<0.05).The maximum PRR value was observed in P50L15 group.The maximum lipid retention rate(LRR)was observed in group P47/L18(P<0.05).Dietary protein/lipid ratio exerted significant interaction effect on LRR(P<0.05).Dietary lipid level affected condition factor(CF)significantly.The maximum CF was observed in 15% lipid group.Condition factor(CF)increased first and then decreased with the increase of dietary lipid.Dietary protein and lipid levels affected fish crude protein and crude lipid significantly(P<0.05).The maximum fish crude protein and crude lipid was observed in50% protein group and 15% lipid group.Dietary protein/lipid ratio exerted significant interaction effect on fish crude lipid(P<0.05).Dietary protein levels affected T-SOD,CAT activity and MDA content of fish liver,muscle,serum,plasma significantly(P<0.05).T-SOD,CAT activity increased with the increase of dietary protein.MDA content decreased with the increase of dietary protein.The maximum T-SOD,CAT activity and the minimum MDA content were observed in 50% protein group.Dietary protein levels affected LZM activity of fish liver,muscle,serum,plasma significantly(P<0.05).The maximum LZM activity was observed in 50% protein group.Dietary lipid levels affected GOT and GPT activity of fish liver significantly(P<0.05).The maximum GOT and GPT activity were observed in 15% lipid group.No significant difference of muscle amino acids was observed among test groups other than tryptophan(TRP)(P>0.05).Dietary protein/lipid levels affected muscle fatty acids significantly other than C20:5n3(EPA)(P>0.05).The electronic tongue test data showed that the dietary protein level had no significant effect on muscle taste(P>0.05).Dietary lipid levels affected muscle comprehensive taste sensor PKS significantly(P<0.05).The maximum PKS response value was observed in 18% lipid group.In summary,for about 400 g of fish,the suitable protein / lipid ratio in dietary was 50% /15%.