Skin toxins in coral‐associated Gobiodon species (Teleostei: Gobiidae) affect predator preference and prey survival

Abstract

Predation risk is high for the many small coral reef fishes, requiring successful sheltering or other predator defence mechanisms. Coral-dwelling gobies of the genus Gobiodon live in close association with scleractinian corals of the genus Acropora. Earlier studies indicated that the low movement frequency of adult fishes and the development of skin toxins (crinotoxicity) are predation avoidance mechanisms. Although past experiments showed that predators refuse food prepared with goby skin mucus, direct predator–prey interactions have not been studied. The present study compares the toxicity levels of two crinotoxic coral gobies – Gobiodon histrio, representative of a conspicuously coloured species, and Gobiodon sp.3 with cryptic coloration – using a standard bioassay method. The results show that toxin levels of both species differ significantly shortly after mucus release but become similar over time. Predator preferences were tested experimentally in an aquarium in which the two gobies and a juvenile damselfish Chromis viridis were exposed to the small grouper Epinephelus fasciatus. Video-analysis revealed that although coral gobies are potential prey, E. fasciatus clearly preferred the non-toxic control fish (C. viridis) over Gobiodon. When targeting a goby, the predator did not prefer one species over the other. Contrary to our expectations that toxic gobies are generally avoided, gobies were often captured, but they were expelled quickly, repeatedly and alive. This unusual post-capture avoidance confirms that these gobies have a very good chance of surviving attacks in the field due to their skin toxins. Nonetheless, some gobies were consumed: the coral shelter may therefore also provide additional protection, with toxins protecting them mainly during movement between corals. In summary, chemical deterrence by crinotoxic fishes seems to be far more efficient in predation avoidance than in physical deterrence involving body squamation and/or strong fin spines.

Quantitative shotgun proteomics distinguishes wound-healing biomarker signatures in common carp skin mucus in response to Ichthyophthirius multifiliis

“…Neoverrucotoxin in fish venom has a mechanism of action where it has been shown to function by forming pores in cell membranes [ 37 ]. The skin toxins in Gobiodon have a range of biological functions, including parasite and predator prevention [ 38 ]. The upregulation of the neoverrucotoxin subunit beta protein was likely to defend fish against the parasite.…”

The hidden half: ecology and evolution of cryptobenthic fishes on coral reefs

“…Most notably, some Elacatinus or Gobiodon gobies can secrete toxic compounds from their skins that appear to be noxious to predators (Colin, 1975;Schubert et al, 2003). As a consequence, predators exhibit comparably low preference for these gobies (Colin, 1975;Schubert et al, 2003;Gratzer et al, 2015). As a consequence of investing into predator defence, the life-history strategies of these gobies may deviate from the short lifespan and high mortality typical of other CRF species (Miller, 1996).…”

Biological and Ecological Roles of External Fish Mucus: A Review

“…Goby epidermal toxins and their ecological implications are well studied and provide a good example of the importance and complexity of fish mucus molecules in ecosystem dynamics. Coral gobies are known to possess different epidermal mucus toxins that exhibit predator deterrence and parasite avoidance [66,161]. Recent studies have shown how goby mucus substances play a key role in the mutualistic association between gobies and corals [162,163].…”

“…Acropora corals use chemicals to attract gobies when attacked by toxic seaweeds, and in turn, gobies trim the seaweed and increase their own mucus toxicity, protecting them against predators and parasites [163]. At the same time, goby skin mucus repels corallivores, protecting corals from predation [161]. However, even though the ecological role of goby epidermal mucus toxins is well studied, their chemical structures are still unknown.…”