Comparison of serum antibody responses and host protection against parasite Ichthyophthirius multifiliis between channel catfish and channel × blue hybrid catfish

There is limited information available on the immune protection of channel catfish Ictalurus punctatus × blue catfish I. furcatus (CB) hybrid against the fish parasite Ichthyophthirius multifiliis (Ich). The objective of this study was to compare serum antibody response and host protection between channel catfish and CB hybrid catfish using a cohabitation model. Channel catfish and CB hybrid catfish were immunized with live theronts by immersion or by IP injection at the dose of 10,000–20,000 theronts per fish in two trials. The fish were then challenged with theronts to compare serum antibody response and protection against the parasite between channel catfish and CB hybrid catfish. The immunized channel catfish and CB hybrid catfish showed a significantly higher (p < 0.05) serum anti-Ich antibody (titer > 1120) compared to non-immunized controls (titer = 0). After being challenged with live theronts, the immunized channel catfish and CB hybrid catfish had none or a low number of the parasites (<50 trophonts per fish) and showed a significantly higher (p < 0.05) survival (90–100%) than non-immunized controls (0%). Overall results indicated that there was no statistical (p > 0.05) difference on serum anti-Ich antibody, parasite infection and fish survival between immunized channel catfish and CB hybrid catfish.