The black saddled toby (Canthigaster Valentini) also known as the saddled toby and valentini’s sharp nose puffer, is a very common sight in Tanzanian waters, being found on reefs, rocky outcrops, lagoons and grass beds. As with other members of the puffer family it swims using its pectoral fins and can make surprisingly fast bursts of speed given its shape. They are found across the Indo Pacific area to the Islands, from 1 meter to 45 meters in depth.
They are often seen swimming fairly close to cover and will dart into a hiding place or swim off at an angle from a person when approached. Once in the hiding spot they will usually turn and watch the diver, waiting for him to swim off.
Black saddled tobies are usually somewhat solitary fish but at times groups of up to twelve or fifteen have been seen milling around in a small area in what is presumably some type of mating behavior as the fish do not appear to be feeding, just swimming around in a ball about five foot wide, each one circling.
Although they are small, they retain an air of confidence about themselves, and can sometimes be seen free swimming far from a hiding place presumably due to the fact that they are highly poisonous, as their liver and skin contain tetrodotoxin which is a very potent neurotoxin. Interestingly, the poison is not produced by the fish itself but by bacteria in the fish which have a symbiotic relationship with the fish.
The toby has a white background with four distinctive bars or saddles across its back, a distinctive yellow tail and a bluish tint on the nose. At times when the light catches it at the right angle it can appear to have a greenish ring around its eyes.
It is an omnivore, and feeds on algae, small tunicates, molluscs and small organisms.
The mimick filefish or black saddled filefish (Paraluteres prionurus) has evolved to mimic the black saddled toby to enjoy the protection offered by the poisonous status of the toby. At times the species swim together and have been known to school. Here is a short video about the two and how to them apart: