Several carapid fishes, known as pearlfishes, are endosymbiotic in holothuroids and asteroids.
Among them, the anemone/clownfish symbiosis is probably the best known (e.g., Mebs, 1994; Elliott and Mariscal, 1997; Cleveland et al., 2011), but another extraordinary example, though less known, is the symbiosis between carapid fishes (Ophidiiformes) and various invertebrates.
A comparison of the histology of gills of untreated and treated fishes showed that the carapid gills were much less altered than those of the other fishes (Figs.
akallopisos) to 16 (in the carapid species) blood vessels flanked by the core of the pillar cells (Fig.
Parmentier and Vandewalle (2005) were the first to test carapid resistance to the presence of Cuvierian tubules.
Contributions to the Biology of Carapid Fishes (Paracanthopterygii: Gadiformes).
Parmentier and Vandewalle (2005) found that the time required for carapids to die when exposed to holothuroid saponins is 2 to 16 times longer than for other fishes and suggested that the resistance of pearlfishes to holothuroid toxins may be related to specializations of the gills.