Eels of the genus Gymnothorax from the Pacific are selectively preyed upon by banded sea kraits (Laticauda colubrina) and have been reported to sustain massive doses of sea krait venom without ill effect. By contrast, the present study found that Gymnothorax moringa from the Caribbean, where no sea snakes occur, are sensitive to sea krait venom, with doses as low as 0.01 mg dry wt of venom/kg wet wt of eel resulting in signs of envenomation, and doses as small as 0.1 mg/kg proving to be lethal. These observations suggest that the resistance of Pacific Gymnothorax to sea krait venom results from coevolution of predator and prey, rather than from a general hardiness of Gymnothorax. This theory is supported further by literature reports of sensitivity to sea snake venom by other taxa of non-coevolved eels that either are allopatric with sea snakes (Anguilla), or are sympatric with them but occupy different habitats and are not preyed upon by them (Heteroconger).