Effects Of Dietary Protein Sources On Feeding Response,immunology Response And Flesh Quality Of Grass Carp (Ctenopharyngodon Idellus)

Grass carp(Ctenopharyngodon idellus) is typically herbivorous, which is a main Chinese freshwater aquaculture fish. Three treatments of feeding experiments including fish meal and plant protein blend(soybean and soy protein concentrate, SPC) diet groups were chose to investigate the effects of fish meal and plant protein blend(soybean and soy protein concentrate, SPC) on growth performance, harmatological profiles, antioandant activity, immunity response, flesh quality and feeding response of grass carp. The control diet was used Peru fishmeal as sole protein source, and use blended plant protein replace 80% and 100% fishmeal, which named as FM, PPB80 and PPB100 diet, respectively. Each diet was fed to 3 replicates with 20 grass carp(initial body weight 153.4±0.3g) for 8-week feeding. There are three parts in this study, the results were respectively summarized as follows:Part 1 The effects of dietary protein sources on feeding response of grass carpAn 8-week growth experiment was conducted to evaluate the effects of dietary protein sources on growth performance, plasma hormone and appetite-related genes expression of grass carp. The results showed that final body weight(FBW), weight gain rate(WGR) and specific growth rate(SGR) in FM group were significantly lower than those in PPB80 and PPB100 group(P<0.05) but feed conversion rate(FCR) was higher(P<0.05). The feed intake showed a reversion from the forth week. No significant difference was observed in daily feed consumption between FM and PPB80 group(P>0.05), but both of them were higher than that of fish fed PPB100 diet during 1-3 weeks(P<0.05); From the forth week to the end of the trial, feed intake was reduced in FM group, and it was significantly lower than those of PPB80 and PPB100 groups(P<0.05). No difference was observed in the concentration of plasma neuropeptide Y(NPY), Leptin or Ghrelin among all treatments postprandial 3h and 6h(P>0.05). However, in postprandial 24 h, plasma Leptin of fish fed FM diet was significantly higher than that of the other groups(P<0.05), and simultaneously, fish fed PPB100 diet showed highest plasma NPY and Ghrelin concentration(P<0.05), which suggested that FM group was in anorexia state in postprandial 24 h, while PPB80 and PPB100 group was hunger and actively feeding. The expression of appetite-related genes in hypothalamus showed that at postprandial 3h Ghrelin/Leptin-NPY/POMC(proopiomelanocorein) signal pathway was activated, the m RNA level of Leptin was up-regulated(P<0.05) while agouti gene-related protein(Ag RP) was down-regulated(P<0.05) in FM group(P<0.05). The opposite expression level appeared in peripheral digestive tract that fish meal diet up-regulated(P<0.05) ghrelin while down-regulated mechanistic target of rapamycin(m TOR) and Leptin(P<0.05). It is suggested that feeding response center cannot make an effective response to the appetite from peripheral is the main reason of anorexia. In postprandial 24 h, the m RNA level of inhibitors Leptin and POMC in hypothalamus showed FM group was significantly higher(P<0.05) while promoter Ag RP was higher in PPB100 group(P<0.05). In digestive tract, the expressions of m TOR, subunit 6 kinase 1(S6K1) and Leptin were up-regulated significantly in FM group(P<0.05). It proved that long-term feeding on high level fishmeal lowered the sensitivity of peripheral and central feeding regulatory system, and then further promoted anorexia of grass carp. In conclusion, the long-term intake of high-fishmeal diet induced anorexia could be the major reason for reduced growth performance during the later stage of experiment. Low fishmeal diet(PPB80) can maintain a continuity feeding and growth. The food intake of PPB100 group was low in the first 4 weeks but a reversal occurred after 3 weeks and maintains an active food intake and rapid growth.Part 2 The effects of dietary protein sources on immunity response of grass carpAn 8-week growth experiment was conducted to evaluate the effects of dietary protein sources on harmatological profiles, antioandant activity and non-specific immune parameters of grass carp.The result showed that high plant protein diet increase activities of alanine aminotransferase(ALT) and lactate dehydrogenase(LDH) in plasma significantly(P<0.05),while high fishmeal diet increase total bilirubin(TBILI) and alkaline phosphatase(ALP)(P<0.05),but the values are within the normal range; Fishmeal promoted Total antioxidant capacity(T-AOC) both in plasma and liver(P<0.05), while the fish oil in fishmeal increased malondialdehyde(MDA) which is the end product of lipid oxidation(P<0.05). In addition, plasma Total superoxide dismutase(T-SOD) was decreased(P<0.05) to destructive free radicals. No adverse effects of dietary protein sources on liver and plasma in others harmatological profiles was observed(P>0.05). High PPB activated immune system that increased Interleukin-8(IL-8), Complement 3(C3),Nitroblue tetrazolium(NBT) and Immunoglobulin M(Ig M) in plasma(P<0.05). There was no significant differences in Interleukin-1α(IL-1α) and Myeloperoxidase(MPO) among groups(P>0.05). In conclusion, Low fishmeal diet(PPB80) could protect immune system of grass carp. Both of high fishmeal and high PPB diet would lead oxidative stress or inflammatory reaction.Part 3 The effects of dietary protein sources on flesh quality on grass carpAn 8-week growth experiment was conducted to investigate the effects of dietary protein sources on final body weight, whole body compositions and flesh quality of grass carp. The results showed that crude lipid of grass carp in PPB100 was lower(P<0.05), while ash was higher than FM group(P<0.05). In addition, flavor amino acid in muscle of FM group was higher than PPB100 group(P<0.05), but no difference was observed in the muscle total free amino acid(TFAA) or biogenic precursor among all treatments(P>0.05). Furthermore, the texture characteristics of raw fillets showed much more significantly difference than those of cooked fillets. The raw fillets in FM groups showed significantly higher hardness, gumminess, chewiness, resilience, drop loss, collagen content and shear force than those of plant protein diets groups(P<0.05). No adverse effects of the texture characteristics on cooked fillets were observed among groups(P>0.05). In conclusion, fishmeal would increase fillet lipopexia. There was no effect on muscle flavor total free amino acids among different protein sources. High plant protein diet could ensure the quality of cooked fillets.