One of the major aquaculture species farmed in Singapore and the region is Malabar red snapper ( Lutjanus malabaricus), which is attracting increasing interest due to its favourable taste, unique red colour and premium prices . However, the quality of fingerlings supplied to the industry is inconsistent. Selective breeding for genetic improvement of production traits has been widely adopted in many key aquaculture species as an approach to increase the quality and productivity of fingerlings. However, currently t here are no selection programmes for Malabar red snapper and to inform future breeding programs it is essential to understand genetic parameters related to commercial traits of interest. Therefore, t he present study estimated genetic parameters of harvest traits for Malabar red snapper with the objective of providing useful information on future genetic improvement programmes of the species.
I n total 2,580 Malabar red snapper cultured at three different rearing sites (tanks in floating barge, sea-c ages and tanks in land-based facility) were genotyped using a newly developed Axiom 70k R ed S napper SNP array, and their body weight (BW) , total length (TL) and intensity of red colouration (CIELAB *a values) were measured before harvest when fish were 18 months old. The mean ( ± SD) of BW , TL and *a values of all fish samples were 632.2 ± 233.3 g , 321.8 ± 68.4 mm and 5.2 ± 6.6, respectively . Heritabilities (h2), genetic correlations (rg ) and genotype by environment interactions (GxE) were estimated using BLUPF90 with an animal model and using the genomic relationship matrix. T he h2 for BW, TL and *a were 0.32 ± 0.04, 0.33 ± 0.04 and 0.03 ± 0.02, respectively . The phenotypic and genetic correlation s between BW and TL were 0. 94 ± 0.00 and 0.95 ± 0.01 , while there was no genetic correlation between BW (nor TL) and red coloration. These results indicated that the harvest growth traits of Malabar red snapper can be improved via selective breeding programs . I n contrast, the very low h2 of red colour suggests that environmental factors (e.g. dietary carotenoids ) rather than genetic effects may be primarily responsible for the phenotypic variation observed in skin redness. Moderate GxE interactions were observed BW (0.50-0.60) and TL (0.14-0.65) among the th ree rearing sites, suggest ing that that a single breeding program may not deliver equal genetic gains for all farms alike, and that genomic selection algorithms should be trained on the rearing site where animals are to be farmed (sea- cages or tank-based systems). In conclusion, the present study provided valuable information for the design of future selective breeding programs for Malabar red snapper.