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Dr. Universe: How can you tell if a fish is female or male? Or if it is a kid or adult or teenager? – Hanaiah, 7, Zhujiang New Town, China
Dear Hanaiah,
There are more than 34,000 species of fish on our planet. It can be tricky to tell the age or gender of a fish, but biologists have come up with a few different ways to find out.
My friend Paul Wheeler, a fish biologist at Washington State University, told me all about it.
Once fish reach an age when they are ready to mate, it is a bit easier to tell whether it is male or female. Females have parts that help produce eggs, and males have parts that help fertilize the eggs. |
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Using an ultrasound, a tool that can capture pictures of an animal’s insides, biologists can look at the fish’s anatomy. They can even tell if a fish is ready to spawn, or deposit, eggs in the water.
There are also some outward characteristics that help us tell the gender of a fish. Wheeler is very curious about salmon. He said male salmon get darker, and their colors are more intense than females. The males also have a big hook on their jaw and sharp teeth.
Researchers can also look at DNA, or genetic information, to learn different things about fish.
“It requires taking a little piece of their fin, and the fins grow back. It’s like taking a little piece of fingernail,” Wheeler said.
It takes time and scientific equipment to analyze the DNA from the fin, but it can help us learn if a fish is male or female.
Wheeler adds that even fins can sometimes signal if a fish is male or female. Male sharks have a pair of fins called “claspers.” Male mollies also have a special set of pointed fins near their rear ends. |
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