Genetic parameters and genotype by environment interaction in a unique Indonesian hybrid tilapia strain selected for production in brackish water pond culture

Recurrent farming failures due to disease outbreaks have driven Indonesian shrimp farmers to develop co-culture between shrimp and tilapia. For this reason the Research Institute for Fish Breeding (RIFB) Indonesia has started to develop a fast-growing tilapia with good growth over a range of fluctuating salinities in brackish water ponds. A freshwater nucleus and evaluation breeding program is the simplest strategy to implement, but requires knowledge on the extent of genotype by environment (GxE) interaction between fresh and brackish water environments. The objectives of this study were: 1) to investigate the presence of GxE between brackish water and freshwater ponds, 2) to investigate the impact of salinity on genetic parameters, and 3) to investigate gonadal development of tilapia in both environments. We produced 91 fish families and for each family, randomly choose 2 groups of 20 fingerlings for communal grow-out in brackish water at salinity 6 to 25 ppt and freshwater for 120–147 days. We recorded harvest weight (HW) and standard length (L) and calculated daily growth coefficient (DGC), growth rate in length (GR(L)) and condition factor (K) for each fish. Gonadosomatic index and maturation score (0/1) was recorded on 6 fish from each family per environment. We estimated genetic parameters using bivariate animal models in ASReml version 4.1. Results: HW, L, DGC and GR (L) in brackish water were significantly higher than in freshwater. Heritability was moderate for all traits in both environments (0.35–0.50). Genetic correlations between brackish water and freshwater for HW, SL, DGC and GR(L) were 0.65–0.74. Gonad weight for males and females, and gonadosomatic index for females in brackish water were significantly higher than in freshwater (P < 0.05). Gonad maturity for both sexes had low heritability in brackish water than in freshwater, (0.12 and 0.04 respectively) with a genetic correlation of 0.47. We conclude that there is substantial GxE interaction for growth between brackish water and freshwater. However, the higher mean growth in brackish water suggests that this is not due to salinity per se, but more likely to other differences between the pond environments. We recommend that a breeding program for salinity tolerant tilapia with a safe, stable, low-risk, and bio-secure fresh water nucleus should incorporate sib information on growth performance in brackish water.