Mucus pH of the tiger pufferTakifugu rubripesis an important factor for host identification by the monogeneanHeterobothrium okamotoi

Abstract

We examined a host-finding factor of the monogeneanHeterobothrium okamotoioncomiracidia to develop an alternative prophylaxis.H. okamotoioncomiracidia attached preferentially to gill filaments and skin mucus from the tiger pufferTakifugu rubripescompared with corresponding material from other tested fishes (amber jackSeriola dumerili, red sea breamPagrus major, Japanese flounderParalichthys olivaceusand spotted halibutVerasper variegatus). The body mucus pH of the tiger puffer was 6·40±0·09 (mean±S.D.), whereas that for the other tested fishes was 7·2–7·4. To find if this difference in pH could account for the specific targeting of tiger puffer byH. okamotoioncomiracidia, the attachment response of the oncomiracidia to pieces of agar buffered at various pH between 6·0 and 7·4 was examined. The number of attaching oncomiracidia was maximal at pH 6·4. We produced gynogenetic tiger puffers from a single female. These gynogenetic individuals showed a variety of body mucus pH and they were exposed to the oncomiracidia. Thirteen days after exposure, more youngH. okamotoiwere found on the gills of gynogenetic tiger puffer with mucus at pH 6·3–6·6, than on gills of fish with mucus at pH 6·0–6·3 and 6·6–7·2.H. okamotoiexploits the body mucus pH to identify the host. The simplicity of pH as a lure may lead to development of a simple and economical method to controlH. okamotoioutbreaks.