Catfish may be one of the most diverse groups of venomous animals on earth, according to a study by University of Michigan graduate student Jeremy Wright published in a recent issue of the journal BMC Evolutionary Biology.
According to the results of Wright's study, which examined the distribution of venom glands associated with the fin spines of catfishes, there are at least 1250 and possibly more than 1600 species of venomous catfishes.
The author examined histological preparations of 158 species of catfishes, biochemical and toxicological analyses of fin spine extracts from several species, and previous phylogenetic studies of catfishes to examine the distribution of venom glands in this group.
Using a maximum parsimony character optimization analysis, the author found venom glands to have evolved independently two or three times within catfishes, and venomous catfishes to possibly outnumber the combined diversity of all other venomous vertebrates.
According to the author, catfish venom show strong similarities with, and might be derived from, previously characterized toxic proteins found in catfish skin secretions. Alternatively, some catfish venoms accelerate healing of wounds, and this may be their primary purpose (with their venomous properties being an added benefit).
For more information, see the paper: Wright, JJ (2009) Diversity, phylogenetic distribution, and origins of venomous catfishes. BMC Evolutionary Biology 9, 282.