Geographic variation in ichthyocrinotoxin from the Estuarine Stonefish (Synanceiahorrida)

Geographic variation in the composition of animal toxins is well documented for venomous taxa, and to a lesser degree, for some poisonous taxa that secrete toxins obtained from their diet. However, very little is known about animals that synthesise their poisons de novo, such as stonefish and their secreted ichthyocrinotoxins. Stonefish are widely distributed throughout the Indo-Pacific, however, the effect of location on the composition of their ichthyocrinotoxin is currently unknown. This study aimed to determine whether the composition of ichthyocrinotoxins from Synanceia horrida (Estuarine Stonefish) varied between three geographically isolated Australian populations including Cairns in far north Queensland, Caloundra in southeast Queensland, and Exmouth in Western Australia. The composition of ichthyocrinotoxins from S. horrida were largely conserved across the three locations, with the size of most of the components falling between 14 and 25 kDa. However, unique components were identified in S. horrida ichthyocrinotoxins from Caloundra and Exmouth populations. Caloundra populations contained unique smaller components (8 and 12 kDa) that were hydrophobic. In contrast, Exmouth populations contained unique larger components (60 and 150 kDa) with no difference in hydrophobicity. We speculate that the composition of ichthyocrinotoxins produced by S. horrida are likely influenced by benthic flora and fauna communities, particularly those that are likely to interact with the animal's skin, such as fouling flora and fauna, as well as parasites. These findings further add to the growing body of evidence underscoring the complexity and compositional diversity of ichthyocrinotoxins produced by stonefish.