Growth performance, survival rate and expression of MHC-I gene in Clarias gariepinus at post Vagococcus carniphilus challenge period

The emergence of Vagococcus carniphilus in Nigeria's catfish farming sparked an investigation into its lethal concentration, effect on growth, and the possible interplay of a genetic factor (MHC-1 gene) in the survival of farmed Clarias gariepinus.

Juvenile C. gariepinus (average weight = 41.04 g; n = 10/tank.) was immersed into a liter of water containing different concentrations of 1, 2, 3, 4, and 5 mL of V. carniphilus isolates in different tanks. Intraperitoneal injection at 1, 2, 3, 4, and 5 mL concentration of V. carniphilus during 96 h was carried out. Time at first mortality and LC₅₀ across different routes were documented and utilized to select the fastest mortality-inflicting route (FMIR). C. gariepinus subsamples (n = 28/tank in triplicate) were challenged with the selected FMIR for 24 h. The challenged and controlled fish were fed to satiation once daily for 28 days. Liver samples of the control, challenged dead and challenged survived specimens were assessed for MHC-1 gene expression.

First occurrence of mortality, mortality rate, and LC₅₀ occurred in respective immersion (p < 0.05) and intraperitoneal injection(p > 0.05) treatments at 3.33 ± 1.52hr (5 mL) to 17.33 ± 3.51hr (1 mL); 11.00 ± 3.60hr (5 mL) to 14.66 ± 4.04hr (1 mL) concentrations. The 5 mL immersion (FMIR) challenged fish had significantly higher FCR (8.12 ± 5.79; 1.69 ± 0.14), but lower feed intake, feed efficiency ratio, weight gained, average daily growth, and relative growth rate. Relative percentage survival ranged from 33.3 (challenged) to 100.00 % (control). The MHC-1 gene expressed at ΔΔCT 5.22 ± 1.54 (dead) and −1.27 ± 0.52 (survivors).

Differential expression of MHC-1 gene across the dead and survived C. gariepinus indicates its relevance as a genetic factor for survival.