剑尾脂鲤 · Swordtail Characin

Overview

Corynopoma riisei is a surface-oriented characid with an unusual reproductive system: males inseminate females, which later release eggs. Male fin extensions and specialized glands make courtship particularly interesting to observe.

Distribution & habitat

It occurs in northern Venezuela, around Villavicencio in Colombia, and on Trinidad. This exclusively freshwater fish inhabits coastal rivers and tributaries. Trinidad records span slow, silty water and clearer flowing habitats.

Aquarium setup

Reserve plenty of open space near the surface despite the fish's modest size. Plant the aquarium with patches of floating cover, adding slender branches and some leaf litter if desired. Soft, mildly acidic water is preferred.

Diet & feeding

The upward-facing mouth and body shape suggest feeding on small surface invertebrates in nature, rather than establishing a fully documented wild diet. Live or frozen water fleas, bloodworms, and copepods are favored in captivity. Most individuals also learn to take dry food.

Behaviour & compatibility

Keep at least six to eight. Males may quarrel occasionally, but the species is otherwise peaceful with suitable companions. Similar-sized characids, cory-type catfishes, small loricariids, and dwarf cichlids can work when their environmental needs match.

Sexual dimorphism

Males develop visible glandular tissue around the tail base, a forward-pointing paddle-shaped appendage near the gill cover, and elongated fins. Small hooks occur on the anal fin. Females lack the conspicuous fin extensions and generally have a rounder abdomen.

Breeding

Condition a mixed group with plentiful small live and frozen foods. Courtship includes movement of the male's gill-cover appendages; females may rub against or nip them. The exact roles of chemical signaling and fin hooks in insemination remain partly unresolved.

For rearing, prepare a separate dim aquarium using water from the adults' tank, fine plants around the edges, an open center, and gentle sponge filtration. After several days of courtship, transfer a couple of females and wait. Females apparently can delay releasing fertilized eggs for weeks until conditions suit them. Eggs hatch in about twenty to thirty-six hours. Remove females once young appear.

Feed microscopic foods for roughly a week, then introduce newly hatched brine shrimp and microworms. Small daily changes with water from the parent aquarium support growth. Broods are usually smaller than in externally fertilizing tetras, possibly because fertilization is more efficient.

Notes

Tail glands release chemicals attractive to females; additional gill glands may also influence courtship. Internal insemination should not be confused with livebearing: eggs are still released and hatch outside the female.