The swordtail characin (Corynopoma riisei), described by Gill in 1858, is a small fish available in fish stores from time to time. Swordtail characins are generally silver but exhibit a range of other colors from gold to shades of blue, depending how the light catches the body. This species is sexually dimorphic, with the male (2 inches in total length) growing larger than the female. As the male matures, his dorsal, anal and pectoral fins become larger. The lower caudal fin develops a number of elongated yellow rays, which give rise to this fish’s common name of swordtail characin. Mature males also develop two fleshy, paddle-shaped maneuverable appendages. These appendages are attached to each gill cover by a narrow, transparent, threadlike extension.
Swordtail characins have been found in the Meta River, which flows along part of the border between Colombia and Venezuela and is part of the Orinoco Basin in South America. Their preferred habitat appears to be the slow-flowing smaller tributaries that have some vegetation, particularly along their banks. Here the water is usually mildly acidic and soft (pH 5.0 to 6.0, dH 1 to 5).
Swordtail characins swim in shoals near the water surface where they feed on small insects that hit the water. They also eagerly eat other small aquatic invertebrates, from Daphnia to insect larvae, as well as small worms.
Swordtail characins have a preference for the upper waters of the aquarium and are active fish — particularly the males, which dart about around their perceived territories. They do not bother other fish species, but two swordtail characin males will partake in fin-flaring exhibitions that liven the aquarium. A group of swordtail characins consisting of perhaps two males and four or five females could be housed in a 35-gallon-long aquarium (36-by-18-by-18 inches) containing other small South American fish species. A tight-fitting hood is required to prevent swordtail characins from jumping out of the aquarium.
To allow aquatic plants to root well, fill the base of the aquarium with 3 inches of smooth gravel. This type of setup offers ample swimming area in the middle and space at the surface for the males to display, while also allowing females to take cover in the plants. Dark gravel will help enhance the subtle colors of the swordtail characins and other fish in the aquarium. Some good fine-leaved plants for this aquarium include Mayaca fluviatilis and stargrass (Heteranthera zosterifolia), and Alternanthera reineckii ‘Red’ will add a lot of color. A low-growing plant suitable for the foreground is the pygmy chain sword plant (Echinodorus tenellus). Fluorescent lighting will be adequate for these plants.
Swordtail characins at your local fish store have hopefully adapted well to local water conditions. Check how the fish are doing before purchasing any and ask about the water in the holding tank. These characins should do well in moderately soft (dH 4 to 8) and slightly acidic (pH 6.0 to 7.0) water. For filtration, use an internal or an external canister filter, and perform 20-percent water changes each month. Use a heater to maintain the temperature between 75 to 80 degrees Fahrenheit. In the aquarium, swordtail characins can adapt to eating flake and other small foods. Offer them live or frozen foods, such as bloodworms, Daphnia, mosquito larvae and brine shrimp, at least once or twice a week. This will keep the swordtail characins in good order and spawning regularly.
Swordtail characins have an interesting way of spawning. The males flash their pair of gill-attached paddles during courtship to attract female fish, and they may even use them to stroke the female. If the female is receptive, the male transfers a packet of sperm to the female, which the female uses to fertilize eggs later when she deposits them among plants. There is no internal fertilization (no fertilized eggs have been found inside females).
One way to accomplish a successful breeding project is to set up a small well-planted aquarium with fine-leaved plants and Java moss. Use water from the main aquarium (pH 6 to 7, dH 4 to 8, temperature 80 degrees), and introduce two or three females, which you should feed well with live food. These females could already be carrying males’ sperm. If so, they will lay eggs among the plants, which should hatch within a day or two.
Carefully examine the plants with a flashlight about five days later to see if there are any tiny fry. They will look like silver slivers darting around among the plants. If there are fry, remove the adult females. Otherwise, introduce male fish for just a day, and then remove the females about three days later, by which time they should have deposited their eggs in the plants.
Success in raising the fry depends on your ability to provide them with the right-sized live foods. Feeding fry is easy, as they eat the microorganisms in infusoria. Alternatively, finely ground flake foods can be provided sparingly, as uneaten food fouls the water. After a few days, they should be able to eat microworms. By day 10, they should be able to eat newly hatched brine shrimp. After this time, they should grow quickly. Water changes, good food and larger aquariums will keep them growing to their full potential.
The beautiful swordtail characins, with their novel way of spawning, are delightful yet hardy fish in the aquarium. They are well worth breeding if only because of their scarcity in the hobby. FAMA
Iggy Tavares started keeping fish more than 40 years ago when he caught some wild guppies in an African stream. His passion is breeding cichlids. He also enjoys writing about his numerous experiences and is an enthusiastic fish photographer.