Hydroxyproline Supplementation On The Performances Of High Plant Protein Source Based Diet In Turbot(Scophthalmus Maximus L)

A feeding trial was conducted to investigate the effects of replacement of differentlevel of fish meal by plant proteins with addition of crystalline hydroxyproline (Hyp)on growth performance, muscle texture, hydroxyproline in tissues and prolylhydroxylase(PHD) concentration in muscle of turbot (Scophthalmus maximus L.).Seven isonitrogenous and isoenergetic diets were formulated: a reference diet (FM)containing60%fish meal and three other diets (40I,50I and60I) based on FM diet inwhich40%,50%and60%fish meal was substituted by a mixture of wheat flour,soybean meal, corn gluten meal, wheat gluten meal, peanut meal and beer yeast.Besides, the same three diets with addition of0.6%Hyp were named40I Hyp,50IHyp, and60IHyp. The final dietary hydroxyproline concentrations were0.23%(FM),0.16%(40I),0.54%(40IHyp),0.18%(50I),0.62%(50IHyp),0.14%(60I), and0.57%(60IHyp). The juveniles (8.63±0.03g) were distributed at a density of30fish peraquarium. Each diet was randomly fed to quadruplicate groups of fish twice daily for8weeks. The main results of the research were summarized as follows:1. Hydroxyproline supplementation on the performance of growth and bodycomposition in turbot (Scophthalmus maximus L.)(1) Effects of experiment diets on growth performance of juvenile turbot: The finalbody weight (FBW) and specific growth rate (SGR) both decreased significantly withincreasing level of plant protein (P<0.05). After adding Hyp in the diets, comparedwith the fish fed diet50I and60I, FBW and SGR of fish fed diet50I HYP and60IHYP (supplement with o.6%Hyp) was significantly improved (P<0.05). Weight gainrate (WGR) decreased markedly with increasing substitution level of fish meal, fishfed diet60I exhibited the lowest WGR (P<0.05). While the supplement of Hyp significantly increased the WGR of fish fed diet in which60%fish meal wassubstituted (P<0.05), no significant difference was observed between fish fed diet FMand60I Hyp (P>0.05).Increasing plant protein significantly lowered protein efficiency ratio (FER)(P<0.05). But it was higher in fish fed diet40I Hyp,50I Hyp, and60I Hyp comparedwith those fish fed40I,50I, and60I. There was no significant difference in PERamong fish fed the seven diets (P>0.05).No differences were observed in feed intake (FI), survival rate (SR), conditionfactor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) in fish fed theexperimental diets (P>0.05).(2) The body composition of the experiment fish:No significantly differences were found in moisture, crude protein，crude lipid andcrude ash contents of whole body among dietary treatments (P>0.05).(3) Apparent digestibility of dry matter and crude protein:The ADC of dry matter and crude protein decreased significantly with increasingreplacement level of fish meal in diet (P<0.05). No significant difference in ADC ofdry matter and crude protein were observed among dietary treatments withsupplement Hyp or not (P>0.05).In conclusion， dietary Hyp supplementation can improve growth performance andincrease the replacement ratio of fish meal in the diet of juvenile turbot conditionally.2. Hydroxyproline supplementation on the muscle texture in turbot(Scophthalmus maximus L.)Muscle texture (including hardness, chewiness and springiness) perform worseafter fish meal substituted compared fish fed diet FM. Triple of them weresignificantly improved, and fish fed diet50I HYP and60I HYP were significantlyhigher in hardness and chewiness than those fed diet50I and60I (P<0.05). Fish feddiets with supplement of Hyp (containing40I Hyp,50I Hyp, and60I Hyp) exhibitedhigher values for springiness than those without (containing40I,50I, and60I)(P<0.05).In conclusion, hydroxyproline supplementation can significantly improve the muscle texture of the cultured turbot.3. Hydroxyproline supplementation on the total Hyp contents in muscle, liver,free Hyp content in plasma, collagen and PHD activity in muscle in turbot(Scophthalmus maximus L.)(1)No difference was observed in total Hyp content of liver in fish fed diet FM,40I,50I,and60I (P>0.05). However, contents of muscle total Hyp and free Hyp in plasmadecreased significantly with increasing substitution level in the diet (P<0.05). Thethree parameters were markedly improved with Hyp supplement in the diets andshowed higher performance than fish fed diet FM (P<0.05).Total Hyp contents in muscle, liver and free Hyp content in plasma weresignificantly affected by the Hyp contents in the experimental diets (P<0.05). Thevariation in content of the above three presented the same trend.Total collagen concentration in muscle was significantly applied to dietary Hyp(P<0.05). Similar to total Hyp content in muscle, the replacement of plant proteindecreased total collagen concentration in muscle compared with fish fed diet FM. Butfish fed diets40I Hyp,50I Hyp, and60I Hyp were significantly higher than othertreatments without supplement of crystalline Hyp in total muscle collagenconcentration (P<0.05), no significant difference was observed among the turbot feddietary with addition of Hyp (P>0.05).(2)Activity of PHD in muscle:No significantly difference was found among PHDactivity in muscle of fish fed the diet40I,50I,60I,40IHyp,50IHyp, and60IHyp inmuscle (P>0.05).In conclusion, dietary Hyp supplementation can improve growth performance andincrease the replacement ratio of fish meal in the diet of juvenile turbot conditionally.Dietary Hyp can improve the muscle texture of the cultured turbot. Addition of Hyp toplant protein-based aquafeeds may be beneficial for maximizing growth and fleshquality of aquatic fish.