Immunological responses of fishes to glochidia of freshwater mussels

Abstract

The immunological aspects of the interaction between fish and glochidia were studied using glochidia of the Alabama rainbow mussel (Villosa iris). Tested host species was the rock bass (Ambloplites rupestris) and non-host fishes were common carp (Cyprinus carpio) and goldfish (Carassius auratus). Ouchterlony double-diffusion tests showed that both the host and non-host species expressed a specific humoral response to glochidial antigens after being artificially infested with the parasites. Further microagglutination tests were completed to compare titers of host and non-host fishes which were either uninfested, infested, or reinfested with glochidia. These tests showed that host and non-host species exhibit humoral responses of similar strengths (similar titers) to glochidia. In addition, fishes infested with glochidia had higher titers than uninfested fishes, and reinfested fishes had titers higher than both uninfested and infested fishes. Results indicate that fishes express anamnestic responses to glochidia.

Because many host-specific parasites mimic their host’s antigens to avoid full immune attack, I tested for antigen mimicry in glochidia. Goldfish were injected with host (rock bass) and non-host (carp) antigens, in the form of sera, and then re-exposed to glochidial antigens at a later time. This test and other experimental results show no evidence of mimicry of host antigens by glochidia before attachment to host fish.

Immunoelectrophoresis (IEP) was used to compare precipitation patterns of host and non-host fishes and to determine whether IEP can be used for identifying suitable hosts for a species of mussel. Although there were subtle differences observed between the precipitation bands of host and non-host fishes using IEP, successful molecular host identification will require more precise electrophoretic methods. The precipitation patterns of glochidial antigens and transformed juvenile antigens (reacted with anti-glochidia fish anti-sera) were compared to determine whether glochidia develop new antigens to avoid a full immune attack during glochidiosis. No precipitation occurred in trials using transformed juvenile antigens; therefore, pre-infestation glochidia and post-infestation juvenile mussels are antigenically different.