Things You'll Need
- Aquarium, heavily planted and equipped with a heater and filter
- Rearing tank equipped with a heater and filter
- Magnifying glass
Instructions
Visit a specialist breeder or a reputable dealer to find a pair of swordtails.
Observe the fish and look for an individual with a modified fin on its abdomen, in the general region of the vent. This fin is long and thin and points backward.
Use a magnifying glass if necessary, because black swordtails mature much later than other swords. The fish with the modified fin, or gonopodum, will be a male. This fish might only be 3 inches long and might not yet possess the long tail fin extension which makes this species so recognizable.
Look for a fish with a rounded fin near the vent. This fish will be a female.
Choose a female black swordtail with clear or colored fins. Black pigment in the fins is associated with fatal tumors.
Choose a male black swordtail with red or orange fins.
Place the fish together in one aquarium and observe them closely for signs of mating; these fish breed readily. Black swordtails are livebearers and the male will fertilize the female internally by placing his gonopodium into her vent.
Watch the female closely to see if she is becoming plump. Gravid females will look visibly pregnant as they begin to fill out.
Place a breeding trap into the aquarium and secure it to the rim with a plastic peg.
Remove the female to a breeding trap approximately 35 days after you observed mating. This small, plastic container allows the young to fall through a false grid floor into a safe area where the female cannot access them, as adult females often eat newly born fry.
Fill the 20-gallon rearing aquarium with water from the main breeding tank.
Set an aquarium heater to 72 degrees Fahrenheit and place it into the rearing aquarium.
Place a sponge filter into a back corner of the rearing aquarium.
Move the fry to their 20-gallon aquarium. You can do this on the day they are born. Scoop the fry up in a small plastic container, as a net may damage their delicate bodies. Some of the young will be solid black with red or orange fins, while others will not have completely black bodies. Avoid further breeding the specimens which do not possess solid dark bodies.
Raise the young that have solid black bodies and choose your next breeding pair from the best specimens in this group of fish. Choose individuals that have the darkest bodies and the most red on their fins. These specimens, known as Berlin swords, are highly sought after among aquarists.