Bactericidal Complement Activity and Concentrations of Immunoglobulin M, Transferrin, and Protein at Different Ages of Channel Catfish

Abstract In this study, we assessed the immune status and natural immunity at different ages in channel catfish Ictalurus punctatus raised in ponds in the southeast USA. Sera were obtained from catfish at 2, 3, 4, 6, and 9 months, and 1, 1.5, 2, 3, 4, 5, and 9 years of age. Catfish immunoglobulin M was quantitated by radial immunodiffusion (RID) according to the Mancini technique. Immunoglobulin M (IgM) was detected by RID at 2 months (1.5 mg/mL), and a gradual increase in IgM was seen until 5 years of age (8.2 mg/mL). Ratios of IgM to globulin remained relatively constant until 3 years of age. Bactericidal activity elicited by the alternative complement pathway (ACP) was determined with Pseudomonas, Escherichia, Aeromonas, and Edwardsiella species. Essentially no difference was seen in percent bactericidal activity against Escherichia and Pseudomonas by the ACP among the different ages of channel catfish. The bactericidal percentages were very high (100°10) against both genera except for Pseudomonas at 2...