Ask patty

Virgin birth?

At the club meeting, Thelma Frias came up to me and asked if there was such thing as a virgin birth in fish? It seems that she had acquired a Piketop minnow (Balanesox belizanus) and had kept it without a mate for six weeks and its previous owner had also kept the fish without a mate for eight prior weeks. Then one a, much to the surprise and delight of its new owner, the fish delivered about 40 half inch babies. This did not seem possible because the time period without a mate was so long.

I hit the books because I knew nothing about this fish and it did not look like the livebearers that I knew. I found that the Piketop minnow is an aggressive predator that does not do well in a community tank. It prefers brackish water with heavy cover and it has a gestation period of 4 1/2 to 7 weeks. So how did this fish deliver after 14 weeks? Well, it seems that some live-bearing fish have a unique breeding method. The male introduces packets of sperm called "spermatozeugmata" which behave quite extraordinarily. Some of the packets will burst and fertilize any ripe eggs present, while others become embedded in the ovarian cavity wall and will remain there until they are needed to fertilize a later batch of eggs. This way a female can have several broods of fry without mating each time.

Although I could not find any literature that said that the Piketop minnow is one of the livebearers that uses this method, it would seem logical that this is the case. Proper water quality and food they have triggered the fish to produce a new brood. Even though this is a very predatory fish, all the literature I read on them says they don't eat their young. I hope Thelma has good luck raising these very interesting fish.

This article originally appeared in the Newletter of the Tampa Bay Aquarium Society, June 1996