Thesis (M.Sc.)--Chulalongkorn University, 2013

Molecular markers that allow selection of juveniles and broodstock with a high breeding value for growth traits are useful for the aquacultural industry. In this study, cellular proteomics of hepatic tissues of large-sized (average body weight = 28.53 ± 12.97 g and average total length = 13.30 ± 1.82 cm, N = 9) and small-sized (average body weight = 2.62 ± 0.74 g and average total length = 6.00 ± 0.55 cm, N = 9) 4-month-old juveniles of the Asian seabass (Lates calcarifer) was examined. In total, 1578 protein homologues were identified and 833 proteins significantly matched either unnamed or unknown proteins (52.8%). The remaining 745 protein (47.2%) matched proteins with known functions. Twenty-eight proteins (e.g. calmodulin cAMP-dependent protein kise catalytic subunit beta, dual specificity phosphatase 6, fidgetin-like protein 1 and clathrin coat assembly protein AP180-like) showed significantly differential expression between large-sized and small-sized samples. In addition, several growth-related proteins, for example, transforming growth factor beta-2 precursor (TGF-β2 precursor), transforming growth factor beta-3 precursor (TGF-β3 precursor), transforming growth factor beta-2-induced protein ig-h3 precursor (TGF-β2-induced protein ig-h3 precursor) and activin type IIB receptor (ActRIIB) were also identified. Single nucleotide polymorphism (SNP) in insulin-like growth factor II (IGF-II), myostatin (MSTN) and ActRIIB was further analyzed in 4-months-old juveniles cultured in concrete tanks (N = 99). Polymorphism of the intron 4 gene segment of IGF-II and MSTN loci 1 did not associated with growth-related parameters. In contrast, large-sized 4-month-old L. calcarifer carrying SSCP pattern B of the exon 1 gene segment of IGF-II possessed a greater average body weight (30.32 ± 15.00 g) than those carrying SSCP pattern C (19.66±5.10 g) (P < 0.05). For MSTN loci 2, results for overall samples revealed that 4-month-old fish carrying SSCP pattern A possessed a greater average body weight, total length and hepatic weight (13.13±11.82 g, 9.32±3.34 cm, 0.19±0.19 g, respectively) than those of fish carrying SSCP pattern B (5.26±7.29 g, 6.65±2.15 cm, 0.07±0.06 g, respectively) (P < 0.05). For ActRIIB, juvenile L. calcarifer exhibiting SSCP pattern D had a greater average body weight, total length and hepatic weight (17.15±13.79 g, 10.24±3.59 cm, 0.24±0.22 g, respectively) than those carrying SSCP genotypes A (2.64 g, 6.10 cm, 0.08 g, respectively) and B (2.95±0.66 g, 6.26±0.64 cm, 0.04±0.04 g, respectively) (P < 0.05). Considering only large-sized juveniles, those exhibiting SSCP pattern D (average body weight 26.38±9.48 g) had a greater growth-related parameters than those exhibiting SSCP pattern C (average body weight 17.77±5.02 g) (P < 0.05). Relationships between SSCP patterns of all examined genes and growth-related parameters were not statistically significant in small-sized fish (P > 0.05). The PCR products of representative individuals exhibiting different SSCP patterns of IGF-II (exon 4) and ActRIIB were sequenced. Results indicated three (A/A72C/C165, G/G72C/T165 and A/G72C/C165) and four (A/G144C/T326, A/G144C/C326, G/G144C/T326 and G/G144C/C326) diplotypes, corresponding to SSCP patterns A-C and A-D of respective genes, were observed. Results demonstrated the potential of SSCP for identification of SNP in interested genes of L. calcarifer.