Orange-striped Triggerfish

The orange-lined triggerfish (Bali (🇮🇩 Indonesia)stapus undulatus) is a demersal triggerfish that belongs to the monotypic genus Bali (🇮🇩 Indonesia)stapus. It is closely related to the genus Balistoides.

The orange-lined triggerfish has a distinct appearance with a dark brown to dark green body adorned with striking orange lines that span from behind its head to the rest of its body. It can reach a maximum size of approximately 30 centimeters. In terms of physique, it has a stocky, oval-shaped body that is laterally compressed. The head is large, accounting for approximately one third of its body length, and it boasts a small terminal mouth with robust teeth. Its first dorsal fin consists of three spines, with one spine longer and stronger than the others. When at rest, this fin can be erected and kept in a dorsal furrow. The second dorsal fin mirrors the size and shape of the anal fin, which is symmetrically positioned opposite to it. The pelvic fin is reduced to a ventral protrusion. The orange-lined triggerfish typically exhibits a large black spot near its peduncular spines, and its caudal fin is orange. Males tend to be larger and lack a concave snout, which distinguishes them from females and juveniles. Additionally, male adults lose the lines on their snouts as they mature.

While other undefinedstoid fishes, such as filefish and leatherjacks, are commonly found throughout the Indo-western Pacific region, triggerfish are typically encountered within coral reef ecosystems, coral lagoons, and external reef slopes within this area. They can also be found off the coasts of East Africa, the 🌊 Red Sea, and 🇯🇵 Japan. Triggerfish tend to reside near their burrows and dens within the reef structure. In coral reef environments, the orange-lined triggerfish display more flexibility compared to other triggerfish species, spanning depths of up to 50 meters, although their preference is for depths ranging from 2 to 8 meters. No correlation has been established between the size of the reef and the depth preferences of juvenile triggerfish. Furthermore, adult triggerfish were found to vary their depth based on the region. In general, this species demonstrates a wide distribution across the reef. It is worth noting that preference for certain substrata differs between adult and juvenile orange-lined triggerfish. Adults typically favor rock and branching coral, whereas juveniles lean towards softer surfaces.

The orange-lined triggerfish is an omnivore with a strong bite, enabling it to consume various benthic prey. Its diet includes cnidarians, molluscs, ctenophores, crustaceans, other fish, algae, and echinoderms. Given its broad diet and distribution, this species plays a fundamental role in coral reef ecosystems through top-down control, particularly in regulating the sea-urchin population. In East African marine parks, the orange-lined triggerfish serves as a primary and dominant predator of the burrowing urchin (Echinometra mathaei). Prior to protection, the triggerfish population was overfished, leading to a rapid growth in the burrowing urchin population. The presence of these sea urchins has detrimental effects on coral reef health, the presence of other grazers and algae, and erosion. In order to avoid potential degradation of coral reef ecosystems, predators like the orange-lined triggerfish are necessary to maintain control over the burrowing sea urchin population. Research indicates that the orange-lined triggerfish consumes more burrowing sea urchins compared to other predators in East African marine parks, which highlights the species' significant impact on coral reef ecosystems.

The orange-lined triggerfish is diurnal, solitary, and territorial in nature. It exhibits aggressive behavior towards other fish and employs the erection of its first dorsal spine as a means of intimidation towards opponents and predators.