Sampson J. E.*, Rhode C.
Department of Genetics, Stellenbosch University, Private bag X1, Matieland, 7602, South Africa
Aquaculture of dusky kob (Argyrosomus japonicus) in South Africa has seen effective response to selection using traditional methods, however parentage assessment using microsatellite markers attributes 67% of a cultured F1 generation to a single breeding pair following mass spawning. The lack of molecular characterisation of broodstock has resulted in high relatedness and creates the potential for inbreeding depression in subsequent generations. This validates previous findings in the species, thus emphasising the need for genetic characterisation of breeding stock. The complex nature of developmental traits such as growth rate requires the inclusion of environmental influences when attempting to characterise genetic variation. Individual responses to stress and behavioural plasticity may serve as key selectors for improved fitness and growth. To this end, analysis of exonic regions for five key genes associated with developmental and neurological pathways in vertebrates was performed in order to better understand the complex biology associated with growth performance in aquaculture. Six SNPs were found to be significantly associated with increases in growth performance, three in bdnf and three in egr1. Haplotypic analysis found strong LD within genes, and an association of egr1 haplotype -GA- with larger individuals (p < 0.01; OR = 21.87, 95% CI: 21.68 – 22.05). A single non-synonymous SNP caused a Serine-Proline (p. Ser119Pro) substitution in the fourth exon of bdnf. This was confirmed (through protein modelling) to significantly alter the structure of BDNF in small individuals, and the mutant protein likely decreased feeding behaviours resulting in this slower growth. A link between neurobehavioral development and growth is apparent, warranting further study in cultured populations.