Tropical Fish Hobbyist - October 2010

to eight fry. I was very excited—though these were once somewhat common fish in the hobby, they are becoming harder to find. This particular group is of even more importance because they are the descendants of fish collected by the late Derek Lambert, given to me when I met him at an American Livebearer Association (ALA) convention.

After their parents had been breeding well for several years, these fish had decided not to have any more fry for another few years, so I was very happy to see the new babies. Ameca is a monotypic genus, meaning there is only one species in the genus, and these fish are extinct in their wild habitat. They were only found originally in a very small area in the Ameca River Drainage in Mexico. There may also be a small population left in a water park in the town of Ameca, and perhaps feral populations in the United States.

While admiring the new A. splendens fry, I couldn’t help but notice the strange, almost tentacle-like appendages hanging from their bodies. These are trophotaeniae, which are comparable to the umbilical cord in mammals. Goodeids are viviparous, meaning that the eggs are retained in the mother’s body as with the poeciliids, but unlike the poeciliids, the unborn goodeids receive nutrients from the mother through the trophotaeniae. These fall off within a few days after birth.

Goodeid males and females also have different anal fin structures. Once again, the females and fry have a regular rounded anal fin, but the male’s anal fin is split, giving these fish the sometimes-used common name “split fins.” The front part of the male split fin is flexible and allows it to fertilize the females. Unlike poeciliids, female goodeids do not store sperm to fertilize multiple broods.

Male Brachyrhaphis rhabdophora; male poeciliids are generally more colorful than females.

Ameca splendens fry with trophotaeniae (organs similar to an umbilical cord) still attached.

There are a number of ways to help increase the number of fry surviving in multigenerational aquariums, however.

Livebearer Breeding Tips

In my aquariums, I generally prefer to keep single species with multiple generations in the same tank. It’s hard enough to maintain multiple aquariums in which to breed several different species, but it’s even harder if each species also needs many tanks.

I have been trying to keep each species in two different tanks as backup in case something happens to the fish in one of them, but dedicating that much space to fishkeeping isn’t always practical.

Hiding Places

When breeding livebearers, you can often increase the number of fry that survive by providing good hiding places for them. I use live plants, which are great because adults may also use them for refuge, and microscopic organisms that grow among the plants serve as supplemental food for the fry.

While almost all plants are helpful, those that provide good top cover are particularly useful with many livebearer fry, many of which will want to spend a lot of time at the surface of the aquarium. In aquariums that are not set up for plants, some floating plants can easily be grown with low lighting as long as the surface isn’t too agitated by filtration or aeration. In hard water, hornwort is often quite easy to grow, and the aquatic fern Ceratopteris thalictroides usually does quite well in softer water; both of these grow well as floating plants. Plastic plants can also help hide fry.

Fish Size and Aggression

Even within a species, the size of the fish can make a difference when trying to keep adult fish from cannibalizing their fry—or even other adults. Some aggressive fish, like many of the Brachyrhaphis and Gambusia species, for instance, will do fine with each other and their fry to a point. But as older females tend to get very large, they also seem to start becoming more aggressive— harassing, killing, and eating smaller fish.

With some of these fish, I’ve found it’s often easier just to have an old ladies’ tank for these larger females to retire in. Large males can sometimes be equally as aggressive, but since the females are often larger than the males in my particular mix of livebearers, I find aggression to be much more common with the females. Among my killifish I often have the opposite problem.

Feed Well

Feeding fish well will also help keep them in good health, improve the health of the fry, and make the fish less likely to prey on their offspring. Feeding a variety of good-quality foods often will help keep larger fish from eating the smaller ones. I’ve never really had troubles with getting most livebearers to eat pretty much any fish food—fresh, frozen, or dried—I put in front of them. Live foods are always appreciated by fish, and they are widely used to encourage breeding.

Remember that when feeding more food, regardless of type, you’re increasing the amount of waste and adding more strain to your biological filter. Be sure to check for any problems with test kits or through visual signs of increased algal growth or fish stress.