Genotype by environment interactions of harvest growth traits for barramundi (Lates calcarifer) commercially farmed in marine vs. freshwater conditions

Barramundi (Lates calcarifer), also known as Asian seabass, is a commercially important tropical aquaculture species farmed in diverse culture production systems and salinities (marine to freshwater). Despite adaptability to different culture conditions, selective breeding programs to improve growth rates in barramundi should consider the impact of genotype by environment (GxE) interactions on genetic gains. Barramundi juveniles from 144 families, originating from 24 dams and 54 sires were farmed in a seawater (SW) raceway in Bowen (QLD, Australia) and a freshwater (FW) pond environment in Townsville (QLD, Australia) - both operated under commercial culture conditions. Fish were sampled at 15 months post-hatch (mph) in the SW raceway (mean 1718 ± 309 g weight (W), 454 ± 28 mm total length (Lₜ) and 141 ± 11 mm body depth (BD) (n = 752)) and at 21 mph in the FW pond (mean 1905 ± 426 g W and 451 ± 39 mm Lₜ and 144 ± 15 mm BD (n = 752)). DNA parentage analyses were used to assign progeny to their respective parents, and the final dataset comprised of 1116 offspring. Moderate-low heritability estimates were found for body traits (W h² = 0.46 ± 0.10; Lₜh² = 0.41 ± 0.12; BD h² = 0.49 ± 0.13; body shape H h² = 0.41 ± 0.12; and Fulton's K condition factor h² = 0.15 ± 0.07). Deformities (Def) were observed in 1.8% of fish in SW and 25.1% of fish in FW, although negligible additive genetic effects were evident (Def h² = 0.05 ± 0.04). GxE interactions were found to be moderate for harvest growth traits (W GxE rg = 0.81 ± 0.11; Lₜ GxE rg = 0.64 ± 0.18; BD GxE rg = 0.78 ± 0.13; H GxE rg = 0.71 ± 0.17), and high for Fulton's K condition factor (K GxE rg = 0.36 ± 0.31; P > 0.05). This study reveals the presence of weak to moderate re-ranking of genotypes for harvest growth traits in L. calcarifer farmed in marine and freshwater conditions, suggesting that GxE interactions should be taken into account in a breeding program servicing multiple environments. Incorporation of sib-information from extreme salinity environments into the selection criteria of a breeding program may therefore optimize the realization of genetic gains across distinct commercial conditions.