The Black Saddled Toby (Canthigaster Valentini) also known as the Model Toby, 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.
They swim using their pectoral fins and although they can make surprisingly fast bursts of speed, they are not strong or fast swimmers. Perhaps to make up for their relative lack of mobility, they have a symbiotic relationship with bacteria such as Pseudoalteromonas tetraodonis. This bacteria produces tetradotoxin which is a powerful neurotoxin. These tetradoxin’s are found in their skin and internal organs. Tetradoxin is extremely poisonous and is approximately 100 times more toxic than cyanide. This gives them protection against predators.
They obtain one of their common names, the Model Toby because they are imitated by the Blacksaddled Filefish (Paraluteres prionurus). You can see how to differentiate between the two species lower down in the post. The Blacksaddled Filefish is not poisonous, but by mimicking the looks of the poisonous Black Saddled Toby it obtains protection.
IN THE WILD
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 Black Saddle Toby has a white background with four distinctive brown-black bars or saddles across its back. Many dots extend across its nose. The tail is a yellow and just behind the eye there is an orange patch with four thin horizontal blue lines . At times when the light catches it at the right angle it can appear to have a greenish or orange ring around its eyes. Thin lines transverse the nose and curve back towards the eyes.
The black saddle tobies are omnivores and feed 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 (the model in this case) to enjoy the protection offered by the poisonous status of the toby. At times the species swim together and have been known to school. Below are some images of the Blacksaddled Filefish which closely resembles the Toby and you can see how to differentiate between the two species here.
In the image below a juvenile of each species some 1.5 cm long can be seen. The toby is the uppermost specimen.
BLACK SADDLED TOBY CLASSIFICATION