In this minute of relaxation, we bring you another Caribbean addition in our series „Take a Minute to relax“. The small but beautiful Monacanthus tuckeri, a.k.a. the Slender filefish.
Although most individuals encountered, range between 2-5cm in length, they can potentially grow up to 10cm! They have laterally compressed, slender, elongated bodies, with a tapered snout, and protruding eyes that are located high on their heads. Filefish have a slender retractable spine on top of their heads, which is incorporated in their first dorsal fin. This spine/dorsal fin actually contains two spines, whereby the second, far smaller one, is used solely to lock the first spine into its upright position. This explains the family name Monacanthidae, from the Greek „monos“ meaning „one“ and „akantha“ meaning „thorn“.
Take a minute to relax with the dancing slender filefish (Monacanthus tuckeri)
Like their cousins the triggerfish, filefish have small gill openings and their pelvic fins are lacking. Instead, there is an extension of the pelvic bone, known as the pelvic rudiment, with skin attached to it. This „pelvic girdle“ is capable of moving up and down in many species, to form a large “dewlap”, which can make Monacanthus appear much larger than it actually is. Some filefish erect the dorsal spine and pelvis simultaneously to lodge themselves into place, making it more difficult for a predator to remove the fish from its shelter. It may also be used for communication purposes with other filefish.
Eats all it can
The small mouths of this creature have specialized incisor teeth, on the upper and lower jaw. In the upper jaw, there are four teeth in the inner series and six in the outer series; in the lower jaw, there are 4-6 in the outer series only. These teeth allow them to be opportunistic omnivores, that dine on macroalgae, filamentous algae, seagrasses, coralline algae, sponges, hydrozoans, bryozoans, and tunicates. A small portion of their diets includes foraminiferans (shelled protozoa), polychaete worms, smaller species of bivalves, snails, ostracods, amphipods, and shrimp.
Avoids being eaten
They have non-overlapping scales that bear “spicules”, which are small, needle-like anatomical structures, protruding from the centre of each scale, giving them the rough and tough, sand-papery skin, that together with its body shape inspired the filefish’s common name. Monacanthus isn’t a particularly strong swimmer, and relies more on crypsis, camouflage, and hiding, to avoid being eaten. Slender filefish are often found around soft corals, like sea whips, rods, and fans, but also in seagrass, hydroids and algae, where they align their movements perfectly with that of the ocean’s swell. Despite lacking the power, their body shape allows them to manoeuvre effortlessly around these complex environments. They love hanging out vertically in the water column, and on top of that, these incredible fish can quickly change their colouration and patterns, making them not easy to find.
But when you find one of these small ocean dancers, enjoy their performance for as long as you can! For it might all be over, in the blink of an eye …