Differential resistance to edwardsiellosis in rohu (Labeo rohita) families selected previously for higher growth and/or aeromoniasis-resistance

Heritability of immunity traits and disease resistance of bighead catfish, Clarias macrocephalus Günther, 1864

Disease outbreak is a major obstruction for intensive aquaculture worldwide. One of the promising solutions is genetic improvement by selective breeding, providing that a sufficient proportion of additive genetic variance (measured by heritability-h²) of disease resistance traits exists. In addition, immunity traits are of interest as potential indirect targeted traits for disease resistance. In this study, the genetic parameters of resistance to Aeromonas hydrophila were reported for the first time in the bighead catfish, Clarias macrocephalus Günther, 1864 which is an important parental species for the production of the commercially important hybrid C. macrocephalus × C. gariepinus. The analyses were performed on 736 data records obtained from 74 full-sib families (31 half-sib families) produced by factorial mating design. The results showed that the heritability of survival rate after disease (Aeromonas hydrophila) challenge (intraperitoneal injection with 0.1 ml containing 1 × 10⁶ CFU/ml of A. hydrophila) was low to moderate (0.05 ± 0.02-0.27 ± 0.15). The immune traits (bactericidal activity-BA, lysozyme activity-LA, and alternative complement activity-ACH₅₀) had low to moderate heritability (h²_BA = 0.05 ± 0.02; h²_LA = 0.16 ± 0.04; h²_ACH50 = 0.31 ± 0.06) while heritability of hematocrit (Hct) was also low (h²_Hct = 0.17 ± 0.04). The results suggested the possibility to improve resistance to A. hydrophila by selection, while the possibility to use immunity traits as indirect selection criteria for disease resistance is still unclear.