Scientists have undertaken a study on sound production in two fish species that live inside sea cucumbers and sea stars.
Carapus acus and Carapus mourlani, two Atlantic and Mediterranean carapid pearlfish species from the cusk eel Order Ophidiiformes, live inside the guts of holothurian sea cucumbers, such as Holothuria tubulosa and Stichopus regalis, and sea stars respectively.
Adult Carapus acus spend most of the day inside the sea cucumber host, but pokes their heads out, or leave entirely, after dark to feed on small fish and invertebrates.
Both C. acus and C. mourlani have a constriction in their swimbladder which forms two distinct chambers, which are used by the fish to produce sounds to allow them to communicate with other fish both inside and outside of the sea cucumber.
Previous studies on the related Carapus boraborensis, C. homei and Encheliophis gracilis, have shown that the fishes produced sounds to allow them to communicate with other fishes.
However, according to the results of a new study by a team of French scientists which has just been published in the journal Acta Zoologica, C. mourlani and C. acus sounds differ substantially from those seen in other carapids.
The pulse length, peak frequency and sharpness of tuning of sounds in acus and mourlani was different to other carapids studied and the sounds were shorter and less repetitive.
The study also looked at the tegument of sea cucumbers to determine whether it would impede the sound produced by the fish, but found that its effects were negligible allowing carapids to produce sounds that could be heard by other fish outside while remaining inside the sea cucumber.
For more details on the study see the paper: Parmentier E, Fine M, Vandewalle P, Ducamp JJ and JP Lagardere (2006) - Sound production in two carapids (Carapus acus and C. mourlani) and through the sea cucumber tegument. Acta Zoologica, Vol. 87. No. 2. pp113.