In this paper assocoations of fishes and sea cucumbers are described. Fish species of the subfamily Carapinae (pearlfishes) find their shelter in sea cucumbers. This subfamily encompassestwo genera of commensal and parasitic species. Various researches have shown that these fishes obtain from their hosts not only protection but also food. While the parasitic fishes of the genus Echiodon eat their gonads, the commensal species of the Carapus genus use the sea cucumber as a bait to attract the tenuis larvae and juveniles to the host. Parasitic species can cause castration of the infected sea cucumbers but due to the regeneration rate these damages are not considered dangerous for the host or the entire population. When living in the intestines or respiratory tract of sea cucumbers no adverse effects on the hosts of nonparasitic pearlfishes were observed, while there is a significant damage on gonads in cases where the fish were in the coelom of the hosts.