Density-dependent effect on oral vaccination of channel catfish against Edwardsiella ictaluri

Replicates of four 0.1-acre (0.04 ha) earthen ponds were stocked with either 6000, 12 000, or 24 000, 13 to 15 day post-hatch channel catfish ( Ictalurus punctatus) per pond. At 6 weeks of age fish in two ponds per density treatment were fed a diet containing 1% of a dehydrated, coated Edwardsiella ictaluri vaccine for 5 consecutive days, then 10 days with normal feed followed by the vaccine feed for an additional 5 days. Four months after stocking, survival in vaccinated fish with 6000 and 12 000 fish per 0.04 ha was 100.6% and 77% compared to 80% and 55.5% for non-vaccinated treatments of the respective stocking densities. Survival of the vaccinates and non-vaccinates stocked at 24 000 0.04 ha was 43.5% and 39.4% respectively. The survivals of vaccinates vs. non-vaccinates within a stocking density were not significantly ( P>0.05) different. Survival in lower stocking densities within a vaccination or non-vaccination regime were significantly ( P