The immune response in fish: a review

The literature relating to the immune response of fish has been reviewed. Non‐specific immune mechanisms similar to those of other vertebrate classes occur in fish. Similarly specific cell‐mediated immunity has been demonstrated at all levels of evolution, from the cyclostomes to the teleosts. A humoral antibody system also occurs in all classes offish but varies considerably in relation to phylogenetic status. In the cyclostomes, only immuno‐proteins with properties intermediate between the immunoglobulms of vertebrates and the non‐specific agglutinins and lysins of invertebrates have been demonstrated. In the elasmo‐branchs and chondrosteans 7 and 19s irnmunoglobulins of IgM type occur. In holosteans the 19s form is predominant whereas in teleosts, 7 and 19s forms occur, with some evidence of specialization in the 7s form. In the phylogenetically most advanced fish, the Dipnoi, two immunoglobulin classes, structurally analogous to IgM and IgG, have been described. A characteristic feature of both cell‐mediated and antibody mediated immune responses in fish is their dependence upon environmental temperature. There is also evidence that, in some species at least, nutritional factors and behaviour patterns may also influence the immune response. Attempts at artificial immunization of fish against infectious disease have met with varied success. It is probable that better results could be achieved with live vaccine strains, particularly if applied under conditions optimal for the immune responses.