title: Effects of Holothuroid Ichtyotoxic Saponins on the Gills of Free-Living Fishes and Symbiotic Pearlfishes.
abstract: Several carapid fishes, known as pearlfishes, are endosymbiotic in holothuroids and asteroids. These echinoderms contain a strong concentration of saponins that are efficient membranolytic repellents to predators. We compared the effects of exposure to saponins from the sea cucumber body wall and from the Cuvierian tubules on the behavior and gill ultrastructure of pearlfishes and free-living fishes. Saponins were extracted from the body wall of two holothuroids, the Mediterranean Holothuria forskali and the tropical Bohadschia atra, and from the water surrounding the Cuvierian tubules of B. atra. Five species of carapids that live in symbiosis with holothuroids and seven species of free-living fishes were exposed to these extracts. The free-living fishes exhibited a stress response and died about 45 times faster than pearlfishes when exposed to the same quantity of saponins. Cuvierian tubules and saponins extracted from the body wall were lethal to the free-living fishes, whereas the carapids were much less sensitive. The carapids did not exhibit a stress response. The high toxicity shown by Cuvierian tubules was not explained by the nature of the saponins that were identified by mass spectrometry, but it is likely due to the higher concentration of saponins in the tubules. Histology and scanning and transmission electron microscopy of the gills of the free-living fishes and pearlfishes showed that saponins act at the level of the secondary lamellae where they induce the detachment of the epithelia, create edema at the level of the epithelia, and induce pores in the epithelial cells that lead to their destruction and the invasion of inner cells (pillar cells and red blood cells). This sequence of events happens 5 min after saponin exposure in free-living fishes and after 1 h in carapids.
authors.affiliation: Biology of Marine Organisms and Biomimetics, University of Mons, B-7000 Mons, Belgium; igor.eeckhaut@umons.ac.be e.parmentier@ulg.ac.be.
authors.forename: Igor
authors.initials: I
authors.lastname: Eeckhaut
authors.affiliation: Biology of Marine Organisms and Biomimetics, University of Mons, B-7000 Mons, Belgium;
authors.forename: Guillaume
authors.initials: G
authors.lastname: Caulier
authors.affiliation: Biology of Marine Organisms and Biomimetics, University of Mons, B-7000 Mons, Belgium;
authors.forename: Lola
authors.initials: L
authors.lastname: Brasseur
authors.affiliation: Biology of Marine Organisms and Biomimetics, University of Mons, B-7000 Mons, Belgium;
authors.forename: Patrick
authors.initials: P
authors.lastname: Flammang
authors.affiliation: Synthesis and Organic Mass Spectrometry, University of Mons, B-7000 Mons, Belgium; and.
authors.forename: Pascal
authors.initials: P
authors.lastname: Gerbaux
authors.affiliation: Laboratory of Morphology, University of Liège, B6 Sart Tilman, B-4000 Liège, Belgium igor.eeckhaut@umons.ac.be e.parmentier@ulg.ac.be.
authors.forename: Eric
authors.initials: E
authors.lastname: Parmentier
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects; D005399:Fishes / Q000502:physiology*; D005880:Gills / Q000187:drug effects* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D012503:Saponins / Q000737:chemistry / Q000494:pharmacology*; D012616:Sea Cucumbers / Q000737:chemistry* / Q000502:physiology*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013559:Symbiosis / Q000502:physiology*
chemical_list: D012503:Saponins