The Blacksaddle filefish (Paraluteres prionurus) is also known as the Mimic filefish or Blacksaddle leatherjacket. Their coloration and shape mimics the poisonous Blacksaddle toby Canthigaster valentini.
This mimicry provides them with protection from predators. Their resemblance is quite similar and a Blacksaddle toby is pictured in the two images below. This form of mimicry is known as Batesian mimicry, where the in this case an edible fish visually mimics a toxic fish species. The species which is being copied is known as the model and the Blacksaddle Toby is sometimes referred to as the Model Toby.
The Blacksaddle filefish which is the mimic is also known as the Mimic Filefish. A juvenile of each species each approximately 2 cm long can be seen below. The Toby with the distinguishing lines on its face is the uppermost specimen. The Blacksaddle filefish is the lower specimen.
Filefish, also known as leatherjackets in Australia are closely related to Triggerfish and Pufferfish. Filefish are in the family Monacanthidae meaning one spine. Similar to Triggerfish, they have a prominent first dorsal spine which can be raised for defense or wedging themselves into a hole. Filefish obtain their name from their rough non overlapping scales which have small spikes on them.
To illustrate the difference between the Blacksaddle filefish, Paraluteres prionurus and the Blacksaddle toby Canthigaster valentine the toby is pictured in the two images below. Note the stripes on the nose which are one of the easier features to distinguish from a distance.
The body shape is very similar to that of the Blacksaddle toby as can be seen in the images. The body is as with most filefish, compressed more laterally compared to the toby which is plumper. The Blacksaddle Filefish has a floral yellow pattern around the eye whereas the toby has concentric rings of green and orange. If one is close enough this is a quick easy way to distinguish the two.
Both have similar looking saddles but the filefish has reticulated patterns below the saddles and on the nose. The toby has lines across the nose and dots on the body. The filefish has a large first dorsal fin which it can raise. The dorsal and anal fins are much longer than those of the toby.
Adult Blacksaddle filefish have small orange hooks in the caudal area which can be seen in the image above. The purpose of these hooks seems to be unknown. The roughness of the skin can also be clearly seen in the image above.
IN THE WILD
The Blacksaddle filefish is a relatively common species in Tanzanian waters. Once one learns to distinguish them from the Blacksaddle Toby you see a lot of them. They often swim together with the tobies and are often seen in pairs swimming above the reef. Occasionally they are seen solitary.
When seen at night they follow the habit of many other filefish and press themselves up against a piece of coral usually low on the substrate. Their coloration does not seem to change at night unlike many other filefish species.
Blacksaddle filefish are found across the Indo Pacific area from the East Coast of Africa to Japan and south to Australia. They are not found in the Red Sea. They are often found in areas where there are large numbers of Blacksaddle Tobies. Both species are usually found in lagoons and on seaward reefs.
The Blacksaddle filefish are omnivores and graze the reef substrate. They additionally feed on small invertebrates, tunicates and sponges. Tube worms , sea star legs and other invertebrates such as sea cucumbers are often nipped in a tank and it is assumed this occurs in the wild as well.
Breeding with filefish usually takes place between one male and several females. The females lay their eggs on the substrate and they are fertilized by the male. The eggs are then guarded by the female to prevent them from being eaten by predators. The Blacksaddle filefish is more often than not seen in pairs in the wild. It seems likely that they differ from other filefish and that the pairs are mated pairs.
Blacksaddle filefish are found in the aquarium trade. They are easier to care for than most other filefish and additionally are not aggressive towards other fish other than their own species. Because of their habit of eating small invertebrates and grazing the reef they are not Reef safe. Tube worms, sea stars and other invertabrates are at risk. As they feed continuously in the wild they require at least three feeds a day. Being omnivores they require a mixed diet to keep them healthy and happy.
BLACKSADDLE FILEFISH CLASSIFICATION
Species: A. scriptus