Sword-cheeked Tetra

About

The swordtail characin (Corynopoma riisei) is a quietly fascinating little fish from the coastal rivers of Trinidad and northern Venezuela, as well as the Meta River basin in Colombia. Males carry a distinctive fleshy appendage on the gill cover that plays a central role in courtship. They extend it and twitch it to attract females, who may respond by rubbing against or even biting the lure. What makes this species genuinely unusual among tetras is that fertilization is internal. Males produce pheromones from specialized caudal glands to draw females in, and once inseminated, females can reportedly retain fertilized eggs for weeks before releasing them when conditions suit them. In the aquarium, swordtail characins are peaceful community fish that do well with other similarly-sized South Americans. Think small characins, Corydoras, dwarf cichlids like Apistogramma, and smaller plecos. Males can be scrappy with each other if kept in small numbers, so a group of six or more keeps things balanced and brings out natural schooling behavior. They settle in well with plenty of cover and will accept a range of foods readily. Not a species you'll find at every fish store, but when they do turn up they're worth picking up. The reproductive biology alone makes them one of the more interesting characins available to hobbyists.