Genetic parameters for growth and survival in rohu carp (Labeo rohita).
Estimates of genetic parameters for growth and survival were obtained from data recorded on 16,718 rohu carp (Labeo rohita), the offspring of 311 sires and 257 dams from seven year-classes. The fish from the first five year-classes (1993 to 1997) were reared in both mono- and polyculture (together with catla and mrigal) earthen ponds, while the three remaining year-classes (1999 to 2001) were reared in monoculture ponds only. The base population year-classes (1993 and 1994) was crosses between a local farmed stock and five river strains. Body weight was recorded at tagging (6 months of age), on a sample of the fish (16 months of age) and at harvest (20 months of age). Genetic correlation between body weight at harvest in the two production systems was very high, 0.96±0.07, indicating a negligible genotype by production environment interaction for growth in rohu. However, the genetic correlation between survival in these two production systems was of medium magnitude, 0.55±0.24, but with a large standard error. Consequently, in a rohu breeding program, the breeding candidates can be selected for growth based on body weights recorded in monoculture ponds. The estimated heritabilities (and of the effect common to full-sibs, c2) across the two production systems were 0.22±0.15 (0.66±0.07), 0.38±0.11 (0.28±0.05), 0.34±0.10 (0.23±0.04) and 0.14±0.05 (0.08±0.02) for body weight at tagging, at sampling, at harvest and survival until harvest (on liability scale), respectively. The large c2 needs to be reduced by rearing each family until tagging size in a more controllable environment, or by pooling a random sample of fry from each family shortly after hatching. The genetic correlation between body weight at sampling and harvest was very high, 0.98±0.01, whereas the genetic correlations of body weight at tagging with body weight at sampling (0.46±0.25) and harvest (0.38±0.27) were of medium magnitude and not significantly different from zero. The low genetic correlations of survival until harvest with body weight at tagging (0.03±0.38), sampling (0.11±0.23) and harvest (0.19±0.22) show that genetic improvement of survival of any significance is only possible through direct selection for survival.