Hermaphrodism is relatively common among forms of marine life
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Take nudibranchs. These snails-without-shells, also called sea slugs, are true hermaphrodites, having male sex organs on one end, female organs on the other. When these creatures have sex, they line up end to end, sometimes several individuals at a time, creating a kind of conga-line orgy.
Fish equipped with both testes and ovaries are called simultaneous hermaphrodites.
One such type of sea bass spawns about 14 times a day. About half the time, the individual releases eggs; the other half sperm. This fish can switch from one to the other in 30 seconds.
black sea bass (1900) found here
As these sea bass grow older, their female gonads grow larger, causing the fish to release more and more eggs and less and less sperm. This probably increases the species’ reproductive success rate since most eggs get fertilized, but most sperm don’t link with eggs.
black sea bass found here
Other simultaneous hermaphrodite fish grow more male tissue as they age. Usually, these fish keep changing, eventually becoming all male. Fish that change sex completely like this are called successive hermaphrodites. Wrasses, parrotfish, some gobies and several other reef fish are in this group.
tattooed parrotfish found here
Successive hermaphrodites perform sex-change acts in a variety of ways, depending upon the species and circumstances.
In clownfish (those cute orange fish that live with anemones), only the largest female and male of a group reproduce. If this large female dies, her mate becomes a female. Then the largest juvenile in the family moves up, becoming the new male.
clownfish found here
Other fish make more than one sex change. In Japanese reef gobies, a female in a group will become male if the dominant male leaves. If a larger male joins the group, the changed fish reverts to her former female self. This sex change takes only four days.
reef goby on brain coral found here
A two-male species, the midshipman of Northern California, has been studied extensively. Type I males take longer to mature, but grow bigger and develop strong vocal systems for courting.
These males, whose gonads account for only 1 percent of their weight, hum to attract females to their carefully built nests.
midshipman found here
Type II males, however, mature early. Their gonads account for a whopping 9 percent of their body weight. (This would be 16 pounds of testicles on a 180 pound man). And humming to attract mates? Forget it. These males use invasion to get mates, stealing both nests, and the females in them, from type I males.
Hermaphrodite fish are on the rise, thanks to the birth control pill and other natural and unnatural forms of estrogen that have made their way into the water. It is believed that it is the female estrogen hormones released from sewage treatment plants that are responsible for the feminization of wild fish.
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