Four Cases of Unusual Crustacean‐Fish Associations and Comments on Parasitic Processes

Abstract Unusual short‐term associations provide insight into the long‐term development or modification of parasitism. A superinfestation of a trap‐held crevalle jack Caranx hippos by juvenile cymothoid isopods Cymothoa oestrum suggested loss of the mechanism controlling numbers of isopods on a host, and overcrowding on the host overcame this isopod's strict site specificity. Crabs (Decapoda) have not been reported as parasites of fishes, but unidentified crab zoeae superinfested the gills of a trap‐held gray angelfish Pomacanthus arcuatus . Adult burrowing crabs Raninoides lamarcki invaded the gills of trap‐held gray snapper Lutjanus griseus ; this suggested how a relatively large crustacean could become an opercular chamber parasite and how wound feeding could occur. An apparent prey‐to‐predator transfer of the cymothoid isopod Anilocra acuta to a free‐swimming king mackerel Scomberomorus cavalla also represented a move from an external to a pharyngeal‐attachment position in this site‐specific isopod. Trap confinement may have protected the infestations of juvenile C. oestrum and crab zoeae from organisms that serve as cleaners. New associations are usually begun by immature stages, but may also be initiated by adult crustaceans, as in the cases of A. acuta and R. lamarcki . The ability of crustaceans to survive, adapt, and be observed makes them excellent subjects for use in discerning complex parasitological processes.