The Smooth Trunkfish (Rhinesomus triqueter) is one of the most beautiful fish found in the reefs around Bermuda. As with most things in nature humans perceive to be beautiful, the trunkfish is extremely toxic, producing a toxin called ostracitoxin.
These colorful fish are not to be confused with the Honeycomb Cowfish, whose patterns and shape mimic the Smooth Trunkfish’s, or the Scrawled Filefish, whose mouth and dorsal and anal fins can be easily confused with the trunkfish’s, though they are much larger than the Smooth Trunkfish. In fact, the Smooth Trunkfish is a member of Ostraciidae, or the boxfish family, of which the cowfish is also a member. This family belongs to the order Tetraodontiformes, containing pufferfish and filefish, so it is easy to see how these species are confused with one another.
The trunkfish’s hexagonal scales are fused to a solid box-like body, however, the Smooth Trunkfish lacks the cowfish’s horn-like protrusions above the eyes which give it its name. Because of the heavy, armored scales that are characteristic of the boxfish family, all fish belonging to this family are limited to slow movement. They make up for this fact, however, with their ability to secrete poison in to the surrounding water.
Unlike the lionfish, which use syringe-like spines to “inject” venom, the poison of the trunkfish is released into the surrounding water. This makes all trunkfish difficult to keep in aquariums because when under stress they will continue to release poison, potentially killing all organisms in a tank, including themselves, due to the inability of the poison to diffuse in such a small space. Despite this, however, trunkfish are edible and are marketed in many parts of the world.
Smooth Trunkfish have “inferior” mouths which allow them to feed on various invertebrates such as mollusks, crustaceans, worms, and sponges. These invertebrates are usually hidden by sand or other bottom-debris, and the smooth trunkfish exposes them by ejecting a jet of water through the mouth, similar to the feeding strategy of a goatfish.
The fish are usually solitary, but easily approachable when found snorkeling or diving. I encountered one a few years ago at Clearwater Beach, Bermuda which was not curious, but certainly not scared of a snorkeler invading its space. The fish possess a calm beauty as adults, and are deliciously cute as juveniles due to their box-like shape.