The pearl fish was recorded in Tunisian water twice. For the first time in Tunisia by Pruvot (1921) during l’ORVET campaign in the East of kélibia. The specimens was caught by a trawl on a muddy bottom at depth between 107 and 113 m. the second specimens was signaled by Lubet and Azzouz (1969) during an experimental trawling study. It was caught in the circalittoral area of the Gulf of Tunis at a depth ranged between 100 and 200 m on a detritic fine bottom. In the Gulf of Gabès the species was reported at about 100 m of depth during an experimental trawling campaign on muddy sandy bottom (Fig. 2). This capture can be considered as the first one in the area. In fact, since 2000 an yearly experimental survey was carried in the area (Hannibal survey). The same hauls were conducted in the same conditions (date, direction, gear…). The species was never being recorded although the commercial portion and the discard part were carefully examined.
The pearl fish live in association with several species of sea cucumbers. This relation is one of the most intimate associations between a vertebrate and an invertebrate host. Carapus acus spend their quiescent hours within the bodies of echinoderms.
Its occurrence in hosts is largely dependent on host availability and its distribution from potential larval areas. In southeastern Spain coast, Stichopus regalis was the only host detected for Carapus acus among six sea cucumber species studied: Holothuria poli, Holothuria mammata, Holothuria tubulosa, Holothuria sanctori, Holothuria arguinensis and Parastichopus regalis (González-Wangüemert et al. 2014). While, Trott (1981), reveal that if the pearl fish Carapus acus have the choice to pick their host they select only H. tubulosa.
It use the sea cucumbers as a protection habitat from predation only or also as a source of food, and to develop into its adult stage of life (Kloss and Pfeiffer 2000).
Parmentier and Das (2004), mentioned that the species leave their host holothurians essentially at night, when they presumably feed. The pearl fish of the Gulf of Gabès was captured in the early morning, sea cucumber weren’t fished during this experimental trawling hauls. While, 11 Holothuriidae were inventoried in Tunisia water, among them, three species are common in the Gulf of Gabès water: Holothuria forskali, Holoturia tubulosa and Stichopus regalis (Ben Mustapha et al. 1999). After the discovery of the pearl fish, the Holothuroidea observed in discard portion were dissected and examined, no pearl fish were detected.