The Niger Trigger (Odonus niger) has a body that can range from dark blue to blue-green in color. Its tail is crescent-shaped, and may develop streamers as the fish matures. The teeth are often red, especially in fish from the Red Sea. These triggers may prey on some crustaceans, sponges, tunicates or very small fish, especially as adults, but do not usually bother corals.
Triggerfish are easily recognized by their distinct body shape and a thick dorsal spike that can be raised and lowered at will. When these fish feels threatened, is ready for sleep at night, or wants to secure itself against strong wave action, it can use the spine to wedge itself into a hole or crevice. Once a trigger has secured itself, it is next to impossible to remove it from its hiding place. These fish may lay on the bottom of the tank or hide in a corner if they can't find an adequate place to feel secure, so they appreciate rock or other ornaments where that can retreat. Use caution when netting these fish as the spines and rough scales can become tangled in the mesh.
Triggerfish are voracious carnivores and will need to be fed a varied diet of meaty foods including freeze-dried or frozen clam, krill, shrimp, and other similar items. They generally cannot be housed with inverts such as crabs, clams, urchins or crabs as these will be seen as a quick snack. Tank mates should be chosen carefully, and they should be large enough and tough enough to hold their own against a feisty trigger.
Be aware that these are very active fish, spending most of their time in the open searching for food or other fish to chase. Some can be downright mean, killing tank mates or biting electrical cords, fingers, or anything else that breaks the water's surface. Be aware of the temperament of any trigger species you may want to house in a tank before they are introduced. Even small triggers can cause big issues as they mature or become established. Triggers from the genera Pseudobalistes, Rhinecanthus, Balistes and Balistoides are generally the most aggressive species and should not be kept with corals, inverts or small fish. Odonus, Melichthys, and Xanthichthys genera are generally less aggressive or destructive and some may even be kept successfully in community or reef aquariums but be aware that they still may prey on inverts (especially crustaceans) or on smaller tankmates.