Abstract
At Makemo Atoll (French Polynesia), the carapid fish Onuxodon fowleri lives in symbiosis with the black-lip pearl oyster Pinctada margaritifera. Although the symbiont seems to live inside its host bivalve by using it as a shelter, additional data are still needed to better understand the exact nature of this association. For this purpose, we implemented an approach using stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N). The δ13C and δ15N values were measured in tissues of the pearl oyster (gonads, gills, mantle and muscles), white muscle tissue from the fish and other food sources. This stable isotope approach was also complemented by the analysis of stomach contents in the carapid fish. Overall, the isotopic compositions measured in the present study support a commensal relationship between O. fowleri and P. margaritifera. In addition, our isotopic data bring new information about another guest living inside P. margaritifera, namely the palaemonid shrimp Conchodytes meleagrinae. Based on the δ13C and δ15N values, it appears that the shrimp might feed on the bivalve gonads.
Highlights
Symbiosis refers to the close association of two different species living together, with organisms being involved as hosts or symbionts (de Bary 1879)
Over the two sampling campaigns, we found a total of 57 O. fowleri individuals sheltered inside the 209 P. margaritifera that were collected on the 13 reef pinnacles
We found that the δ13C values of O. fowleri did not match the isotopic composition of small benthic invertebrates collected in the vicinity of the pearl oysters
Summary
Symbiosis refers to the close association of two different species living together, with organisms being involved as hosts or symbionts (de Bary 1879). Pearlfishes (Ophidiiformes: Carapidae) are eel-like fishes that mainly occur in shallow to moderately deep waters of tropical seas (Markle and Olney 1990) Within this family, several genera (Onuxodon spp., Carapus spp. and Encheliophis spp.) share a remarkable peculiarity: they are able to penetrate and live inside different invertebrate hosts such as echinoderms (holothurians, starfish) and bivalves (Fowler 1927, Tyler 1970, Trott and Trott 1972). The exact nature of this host/symbiont association has not yet been experimentally demonstrated and additional data are needed to gain further insight into the type of symbiosis taking place
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