Study About Regulation Of Dietary Soy Protein Concentrate On Feed Intake And Protein Metabolism In Juvenile Darkbarbel Catfish (Pelteobagrus Vachelli)

Darkbarbel catfish (Pelteobagrus vachelli) is a widely farmed freshwater fishspecies with important commercial value in China. This study is aimed to investigatethe how dietary soybean protein concentrate regulates feeding and protein metabolismof darkbarbel catfish based on the molecular biology technique and feeding andgrowth experiments. The key gene regulation of feeding and metabolism of protein indarkbarbel catfish is acquired by homologous cloning technology. On basis of this,study was conduted to investigate the effects of different protein sources (soybeanprotein concentrate, fish meal, hydrolysis of fish protein and amino acid mixture) ongrowth, survival and expression of some feeding and protein metabolism relatedgenes. The aim of these experiments is to clarify whether or not soybean proteinconcentrate is through the influence of darkbarbel catfish feeding process to controlthe growth and metabolism of protein, and further provide the theoretical foundationfor darkbarbel catfish industry sustainable development. The results are summarizedas follows:1. Molecular cloning, characterization of some feeding and protein metabolismrelated genes in juvenile darkbarbel catfish (Pelteobagrus vachelli)In the present study, the cDNA of NPY, PEPT1and the core sequence of TORfrom darkbarbel catfish (Pelteobagrus vachelli) were cloned by homology cloningwith degenerate primer and RACE techniques. The full-length cDNA of NPY was of661bp, including an open reading frame (ORF) of285bp encoding a polypeptide95amino acids with predicted molecular weight of10.82kDa and theoretical isoelectricpoint of5.8. BLAST analysis revealed that NPY shared high similarity with otherknown NPY, but the N-amino acids portions appeared to be quite variable. Thefull-length cDNA of PEPT1was of2728bp, including an open reading frame (ORF)of2160bp encoding a polypeptide720amino acids with predicted molecular weightof80.95kDa and theoretical isoelectric point of5.47. BLAST analysis revealed thatNPY shared high similarity with other known NPY, but the N-amino acids portionsappeared to be quite variable. The core sequence length of TOR was594bp encoding a polypeptide198amino acids. The foregut had the highest PepT1mRNA levelamong ten tissues in this study. Cloning of the genes could contribut to explain themechanism of feed nutrition explains the regulation of feeding and proteinmetabolism in darkbarbel catfish from molecular angle.2. Compative studies on effects of SPC and other three protein sources on growthperformance, survival, expression of protein metabolism related genes injuvenile darkbarbel catfish (Pelteobagrus vachelli)In the present study, a66-day feeding trial in recirculation rearing system wasconducted to investigate the effects of dietary protein source on survival, growth andforgut PepT1gene mRNA expression levels of juvenile darkbarbel catfish (initialweight2.90±0.01g). Six isonitrogenous (crude protein40%) and isoenergetic (19.5kJ g1) practical diets were formulated by replacing protein from fish meal (thecontrol) with soy protein concentrate (SPC), fish hydrolysate, amino acids. Each dietwas randomly fed to triplicate groups of fish, and each cage was stocked with60fish.Fish were fed twice daily (07:00and18:00) to apparent satiation. The results showedthat no significant differences were observed in survival among dietary treatments.However, different dietary protein had a significant effect on SGR. SGR on day35and day66in fish fed the diet with fish meal was significantly higher than othergroups, while the fish hydrolysate treatment had the lowest level (P <0.05). Theforegut PepT1mRNA expression levels on35day followed the same pattern as SGR,but results of day66analysis showed the foregut PepT1mRNA expression levelsdeviated with different dietary protein. The foregut PepT1mRNA expression level ofSPC100%treatment was significantly higher than other groups and the fishhydrolysate treatment had the lowest level (P <0.05). The results from the presentstudy suggested that the higher forgut PepT1mRNA expression levels could beattributed to explanation the fact that juvenile darkbarbel catfish fed SPC had bettergrowth performance than those fed FH and FAA.3. Effects of different dietary SPC levels on growth performance, survival,expression of feeding and protein metabolism related genes in juveniledarkbarbel catfish (Pelteobagrus vachelli)In the present study, a66-day feeding trial in recirculation rearing system wasconducted to investigate the effects of dietary SPC levels on growth performance,suivival, hypothalamus NPY gene and forgut PEPT1gene mRNA expression ofjuvenile darkbarbel catfish (initial weight2.90±0.01g). Three isonitrogenous (crude protein40%) and isolipid (crude lipid9%) semi-purified diets were formulated byreplacing protein from fish meal (the control) with gradient soy protein concentrate(SPC)(100%and40%level), and were named FM, SPC40%and SPC100%. Eachdiet was randomly fed to triplicate groups of fish, and each cage was stocked with60fish. Fish were fed twice daily (07:00and18:00) to apparent satiation. The resultsshowed that different dietary treatments did not play any significant effects onsurvival, but did show a significant effect on FI and SGR. FI and SGR on day35continued to decrease with the increasing replacing level, among which FM showedthe largest value but SPC100%showed the least value. The results on day66weresimilar to those on day35, although FM and SP40%showed the similar FI value andSPC40%showed the largest value of SGR. The results of forgut PEPT1gene on day35showed were similar to SGR on day35, however forgut PEPT1gene on day66continued to increasing with the increasing replacing level, among which SPC100%showed the largest value. Moreover, hypothalamus NPY gene on day35and66bothshowed a continued decrease with the increasing replacing level, with the largestvalue in FM but the least value in SPC100%..In addition, liver TOR gene expressionlevel was not significantly affected by diatery SPC levels. The results from the presentstudy suggested that the decreased patality caused by decreased NPY mRNAexpression level was one reason for that fishmeal replacement by dietary SPCinfluenced the growth of juvenile darkbarbel catfish.4. Effects of feed restriction on growth performance, survival, expression of somefeeding and protein metabolism related genes in juvenile darkbarbel catfish(Pelteobagrus vachelli)In the present study, a66-day feeding trial in recirculation rearing system wasconducted to investigate the effects of feed restriction on feed intake, growth,hypothalamic NPY mRNA and forgut PEPT1gene mRNA expression levels ofjuvenile darkbarbel catfish (initial weight2.90±0.01g). Fish from the control groupwas fed to apparent satiation. In the experimental treatments, feeding rates wasreduced to50%of the control group or fully hunger, and the three diets were namedas apparent satiation, apparent satiation50%and hunger, respectively. Fish were fedtwice daily (07:00and18:00). Fish from the hunger group was refed to apparentsatiation after35-day fasting. The results showed that no significant differences wereobserved in survival among dietary treatments. SGR, FI and the foregut PEPT1genemRNA expression levels on day35all decreased with increasing feed restriction levels. However, the hypothalamus NPY gene mRNA expression increased gradually(P <0.05). After29days of refeeding, the SGR on day66of maximum valueappeared in the hunger group, the foregut PEPT1gene mRNA expression level alsoincreased significantly. However, the hypothalamus NPY gene mRNA expressionlevel decreased and was significantly lower than that in50%apparent satiation group(P<0.05).The results from the present study suggested that NPY gene had a role topromote appetite in juvenile darkbarbel catfish and had effects on PEPT1gene mRNAexpression.