Count Your Eggs Before They Hatch: Fecundity Differences in Two Species of the Livebearing Fishes of the Genus Gambusia
Date
2008-04-26
Authors
Garee-Boyles, Sophia
Tracy, Stephanie
Hornung, Rachel
Deaton, Ph.D., Raelynn
Journal Title
Journal ISSN
Volume Title
Publisher
Sam Houston State University. Elliott T. Bower's Honor College
Abstract
Description
Fertilization in Gambusia species is internal and the young develop inside the mother until they emerge as small free-swimming fish. The gestation period for these fish usually ranges from about 22-25 days, but can be as long as 50 days, depending on water temperature, season, and location. Females must become sexually mature in order to produce offspring, and this can take up to 8 months, depending on water temperature and other variables. Mature females have a dark spot (gravid spot) on the side of their abdomen, above the gonoduct, whereas mature males have a modified anal fin to transfer sperm to the females (called a gonopodium). The larger gravid spots on the females indicate higher levels of sexual maturity. Fecundity is also influenced by levels of nutrition. The more food available, the larger the brood mass potential. The Western Mosquitofish, Gambusia affinis, is known for their ability to survive in environments that fluctuate drastically in temperature and available nutrition. The largespring gambusia, G. geiseri are known to inhabit warmer springs and have a longer reproductive season. In our experiment, we examined 10 G. affinis and 10 G. geiseri, dissecting them to measure the number of eggs and embryos, and their stage of development. As we predicted, the G. geiseri had more eggs and embryos in various stages, probably due to their earlier breeding season. We also found that there were more gravid G. geiseri than G. affinis. This could be due to other variables such as temperature and nutrition. Our data showed significant variations between the broods in both species and their development stages.
Keywords
Reproduction, Fishes--Spawning, Gambusia geiseri, Mosquitofish