Fish Have Sex in a Variety of Ways
Fish Reproduce With Many Options
Fish sex is a mystery to many and indeed fish reproduce in a manner somewhat different from humans. There are female fish who produce eggs, or in fish lingo, roe; and there are male fish who produce sperm, also known as milt. There are also hermaphroditic fish that have both sex organs at the same time. Due to their aquatic environment, most fish opt for external fertilization although some fish, sharks, and rays do develop babies internally.
How Do Fish Reproduce Through External Fertilization?
Roughly 90% of bony fish reproduce through external fertilization or oviparity. In oviparity the female develops millions of eggs and either lays them on a substrate or casts them out into the water. Males will then release their sperm into the water and if the fish are lucky, eggs and sperm will meet. Most male fish do not have penises; rather sperm are released through the urogenital opening. There are some obvious disadvantages to this system of fish sex. The fish don’t have much control over the meeting of egg and sperm. Also, the babies will hatch into larvae that must fend for themselves – obtaining their own food and avoiding predation. Out of the millions of eggs laid only a few might make it to adulthood. However, this method of fish sex does allow the animals to take advantage of their aquatic medium.
How Does Internal Fertilization Work For Fish?
Some fish fertilize eggs within the mother and this type of fish reproduction better coincides with the traditional idea humans have of sex. In this method the males do have an organ for sperm transfer. It’s not called a penis but a gonopodium, however its function is essentially the same. Internal fertilization can follow through in two ways, ovoviviparity and viviparity. In ovoviviparity there is no direct maternal nourishment through a placenta. The developing young feed on the yolk just as fish developing externally do. However, having the egg develop within the mother can protect it from predators. The disadvantage is that the mother isn’t able to develop as many eggs as fish practicing oviparity do. Often with fish using ovoviviparity the young are still hatched as larva. One example of a fish using ovoviviparity is the rockfish.
Can Fish Have Live Births?
The other method of internal fertilization is viviparity. In this case the mother directly nourishes the eggs through a structure analogous to a mammal’s placenta. Also, the baby fish are born fully formed. Many species of sharks, although not all, have live births. Sharks do fertilize internally though and in this case the male sexual organ is referred to as claspers. Guppies are different from sharks in many ways, but they too give live births.
The reproductive lives of fish vary by species and fish have many options to choose from. It just goes to show that fish sex is another interesting wonder of the natural world.
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