On the biology of the pearlfish Carapus acus (Brunnich, 1768) (Carapidae, Teleostei), with indications of a non-parasitic nutrition.

450 Stichopus regalis (Cuvier), caught with a trawl-net at a depth of 70-11 0 m off Banyuls-sur-mer (France) contained 38 Campus acus. We found only tw o pearlfish in 85 Holothuria tubulosa Gmelin caught in less than 10 m of se awater. We kept pearlfish in aquaria and analysed their behaviour by means of computer analysis of video records. The manner by which the fish enter t heir hosts was studied (see summary). In the wild most specimens of C. acus are found in S. regalis, yet in our aquaria C. acus only entered H. tubulo sa if they could choose between both species. We studied the stomach conten ts of C. acus and found crustaceans. The stomachs examined did not contain any holothurian tissue. Our results give reason to agree with Emery (1880), who stated that C. acus is an inquiline, to whom the host holothurian serv es as a shelter only.