Effect of Saprolegnia parasitica infection on immuno-biochemical parameters and disease resistance capacity of Labeo rohita fingerlings.

The oomycete water mold Saprolegnia parasitica poses a considerable threat to the global aquaculture industry, leading to substantial economic losses. This study aimed to investigate the effects of experimental S. parasitica challenge on key immunological, biochemical, and hematological parameters, as well as disease resistance, in fingerlings of Labeo rohita, an important freshwater carp species farmed across Southeast Asia. The study used a strain of S. parasitica isolated from L. rohita to challenge healthy juveniles (10.2 ± 2.1g) through different infection routes such as injection, cohabitation, and immersion exposure. Analyses of blood parameters on days 15, 30, and 45 post-infection revealed significant changes (P≤0.05), including increased blood glucose, decreased serum protein, albumin, and lysozyme activity, and variable serum bactericidal activity in infected fish. Infected fish also showed reduced hemoglobin concentration and erythrocyte counts compared to uninfected controls, leading to a mortality rate of about 55 % by day 45 post-infection. These findings suggest that S. parasitica infection can impair immune function in L. rohita fingerlings, potentially hindering the growth of the aquaculture industry reliant on this species. Future research should focus on identifying genetic and environmental factors influencing disease susceptibility, evaluating preventive and therapeutic measures, and exploring associated histopathology.