Immunization of Fishes: a Review

Immune response in fishes, which are ectothermic animals, depends on temperature. The optimum response is at the optimum temperature for the species. It is, however, slower in coldwater fishes, such as salmonids, and faster in warmwater fishes. Serum of fishes contains proteins very similar, but not identical, with those of mammals. Immune bodies are contained in gamma, beta, and alpha globulins. Gamma globulin is absent in some fishes. Fishes can be effectively immunized by injection of antigens, however, this is not a practical method. For this reason oral immunization has been attempted repeatedly but the effectiveness is variable.

Immunity to Eimeria tenella and Eimeria necatrix infections in the fowl. I. Influence of the site of infection and the stage of the parasite. II. Cross-protection

Resistance to E. necatrix induced by complete life-cycle infections was transferable from duodenum to caeca and vice versa.

Complete life-cycle infections with E. tenella protected against subsequent attempts to infect with 2nd-generation merozoites. A similar experiment using E. necatrix showed a partial effect.

E. necatrix gametogony-only infections did not protect against subsequent gametogony-only infections and did not protect against schizogony in the duodenum. They did suppress oocyst production resulting from entire life-cycle infections.

Satisfactory oocyst production from the intra-caecal inoculation of second generation E. necatrix merozoites was not obtained.

Repeated oral infections with E. tenella or E. necatrix reduced subsequent cross-infections with E. necatrix or E. tenella respectively by approximately half. Both schizogony and gametogony stages were affected.

A similar result was obtained with E. tenella oocyst inoculation when previous infections were initiated by the intra-caecal injection of E. necatrix sporozoites.

Oocyst production from the oral administration of E. tenella oocysts to birds previously infected with gametogony stages only of E. necatrix was much reduced but the schizogony stages of the challenge infection were not appreciably affected. Previous repeated caecal inoculation of E. necatrix merozoites did not reduce oocyst production from subsequent inoculations of E. tenella merozoites or of E. necatrix merozoites.

Thanks are due to Mr P. L. Long for his interest and advice. The excellent technical assistance of Mr Brian Millard and other members of the Parasitology Department is also gratefully acknowledged.