Effects Of Dietary Methionine On Growth Performance And Methionine Metabolism Of Juvenile Darkbarbel Catfish (Pelteobagrus Vachelli)

Darkbarbel catfish (Pelteobagrus vachelli) is widely farmed in China. Study wasconducted to investigate the effects of dietary methionine on survival, growthperformance and methionine metabolism. The experiment content and results havebeen presented as follows.1. Molecular cloning, characterization and the tissue distribution of methioninemetabolism genesIn the present study, the cDNA of methionine metabolism gennes from darkbarbelcatfish was cloned by homology cloning with degenerate primer and RACEtechniques. The full-length cDNA of methionine adenosyltransferase (MAT1A,KJ489307) was of2427bp, including an open reading frame1173bp,5’UTR172bpand3’UTR1082bp, encoding a polypeptide390amino acids.729nucleotides ofbetaine-homocysteine methyltransferase (BHMT, KJ489308),501nucleotides ofmethionine synthase (MS, KJ489309) and920nucleotides of cystathionineβ-synthase (CBS, J489310) were also obtained. Quantitative PCR (qPCR) was used toassess the tissue distribution of methionine metabolism genes. The results showed thatliver was the highest expression tissue, stomach was the lowest one. The mainexpression tissue of methionine metabolism is liver.2. Effects of dietary methionine on survival, growth performance andmethionine metabolism in darkbarbel catfishSix isonitrogenous and isolipidic diets were formulated with supplementation of0.0,0.3,0.6,0.9,1.2and1.5%methionine, and the final dietary methionineconcentrations were0.40,0.73,1.04,1.33,1.70and1.98%, respectively. Nosignificant differences in survival, body composition, hepatosomatic index, activitiesof liver glutamic oxalacetic transaminases (GOT), contents of liver glutathione (GSH)and activities of plasma lysozymes were found. On the basis of specific growth rate(SGR), the optimum dietary methionine requirements of juvenile darkbarbel catfish was estimated using second-order polynomial regression analysis to be1.36%of diet(3.25%of dietary protein). With increasing dietary methionine, activities ofglutamic-pyruvic transaminase (GPT) in liver increased significantly, and the highestvalue was found in fish fed the diet with1.70%methionine (P<0.05). As dietarymethionine increased, activities of plasma GPT first increased and then keep stable,and the break point was found in fish fed the diet with1.04%methionine (P<0.05).As dietary methionine increased, activities of plasma GOT first increased and thendecreased, and the highest value was found in fish fed the diet with0.73%methionine(P<0.05). Methionine adenosyltransferase (MAT), cystathionine β-synthase (CBS)and methionine synthase (MS) expression in liver were significantly up-regulatedwith increasing dietary methionine (P<0.05). There was no significant difference ofbetaine-homocysteine methyltransferase (BHMT) in liver (P>0.05).3. The spare value of cysteine for methionine at a constant total sulfur aminoacidsThe1.33%methionine diet was as basal diet, the ratio of cysteine replacement formethionine were0%,25%,50%,75%and100%. The final dietary methionineconcentrations were1.30,1.08,0.85,0.63and0.40%, and the final dietary cysteineconcentrations were0.34,0.56,0.79,1.01and1.24%. No significant differences insurvival, body composition, hepatosomatic index, activities of liver glutamicoxalacetic transaminases (GOT), contents of liver glutathione (GSH) and activities ofplasma lysozymes were found. On the basis of specific growth rate (SGR), theoptimum dietary cysteine requirements of juvenile darkbarbel catfish was estimatedusing second-order polynomial regression analysis to be0.77%of diet (1.84%ofdietary protein). The spare value of cysteine for methionine supplementation was50%,48%of total sulfur amino acid (TSAA). With increasing dietary cysteine, activities ofglutamic-pyruvic transaminase (GPT) in liver first increased then decreased, and thehighest value was found in fish fed the diet with0.79%of diet (P<0.05). As dietarycysteine increased, activities of plasma GOT and GPT first decreased and thenincreased, and the lowest value was found in fish fed the diet with0.79%of dietcysteine (P<0.05).