Mailfish

About

The mailfish (Cleidopus gloriamaris), also widely known as the pineconefish or knightfish, is one of the more unusual-looking animals you can keep in a marine aquarium. Its body is encased in thick, interlocking scales that genuinely resemble a pine cone or a suit of plate armor, and the lower jaw carries a pair of bioluminescent organs that glow green-to-red. Earning it the nickname "port and starboard light fish" among Australian fishers. In the wild it lives along the Australian coastline from the eastern Indian Ocean into the western Pacific, spending daylight hours tucked under rocky ledges, inside caves, or hovering in shaded overhangs on reefs and occasionally over muddy bottoms. That secretive, low-activity lifestyle carries right into the aquarium. Expect this fish to stay hidden through much of the day and become more active once the lights dim. It is a carnivore that needs meaty foods, but its temperament is peaceful and it poses no real threat to tankmates. Despite the unusual biology and the marine setup it requires, the species is listed as beginner-appropriate, suggesting it adapts reasonably well to aquarium conditions when its need for hiding spots and low-light retreats is respected.