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Fatherly Fish

Fatherly Fish

In the hit movie Finding Nemo, Marlin the clown fish searches the ocean for his missing son. While it's unlikely that a real clown fish could make this long journey, some male fish do show a fatherly attitude toward their offspring. You'll hear about one in this Science Update.


Transcript

A fish's fatherly instincts. I'm Bob Hirshon and this is Science Update.

Fish aren't known for their parenting skills—most abandon their eggs once they've been laid. But it turns out that some fish dads take pride in parenting, even flaunting their abilities to attract new mates.

That's according to University of Florida zoologist Colette St. Mary. She says the sand goby, a common fish found in Europe, watches over its eggs until they hatch.

St. Mary:

So a good father has a nest which he's defending. And he also is fanning the eggs and cleaning them, basically rubbing his body against them, fanning them with his fins, which moves water through the nest.

But even with all this babysitting, these fish fathers aren't missing out on further mating opportunities. St. Mary and her colleagues found that when a female goby swims by, these dads actually step up the good-father routine, as if trying to impress the female.

St. Mary:

This is evidence that males of this species are using care very much like they use courtship. They are providing more care in the presence of mating opportunities, than in their absence.

The researchers are now testing to see whether all this showing off really does increase a male's chances with the ladies. For the American Association for the Advancement of Science, I'm Bob Hirshon.


Making Sense of the Research

Although the families on Jerry Springer might suggest otherwise, human fathers are actually pretty dedicated by animal standards. In mammals and birds, it's usually the female who takes care of the offspring, while the males mostly look out for new mating opportunities. That's partly because females can have only a limited number of offspring, so it pays for them to take good care of them, while males can have almost unlimited numbers of children, as long as they get around the block enough times.

In fish, the story is a little different, because females lay hundreds or even thousands of eggs at a time, and the males come along and fertilize the eggs later. As a result, many fish don't parent their offspring at all—by the time they hatch, mom and dad could be far across the sea. What's striking is that among fish who do show parenting behavior, the dads seem to be more dedicated than the moms. For example, you've probably heard that male, not female, seahorses carry eggs in their pouch.

The sand goby is another interesting example. As St. Mary points out, they perform a number of elaborate parental care behaviors. And they seem to step it up whenever females are around. This could explain why it's advantageous for males to take care of their eggs: doing so helps them get more chances to mate, and therefore many more offspring.

An interesting detail that wasn't mentioned in the story is that sand goby dads sometimes eat their eggs while they're taking care of them. This sort of cannibalistic behavior is relatively common among fish—after all, if you're sitting around guarding eggs all day, you're going to get hungry, and it might be better to eat a few eggs than to abandon them on a food hunt and risk losing them all. But St. Mary found that the more females there are nearby, the fewer eggs the males eat. Could they be restraining their appetites in front of the ladies? Are they trying to send the message: "Hey, mate with me, I won't eat your eggs—well, most of them, anyway"?

That's the sort of question St. Mary would like to ask in her next experiments. It's clear that the males respond to the presence of females by trotting out their daddy act, but do the females buy it? She'll try to answer that question by isolating male fish and recording females' responses to each kind of fatherly behavior they display. If acting like a dad really does spark the female gobies' interest, that would help explain why the guys like to show off.

Now try and answer these questions:

  1. What are some examples of fathering behavior in sand gobies?
  2. What are the possible benefits of the fathering behavior? Which explanation best fits the evidence available so far?
  3. Describe an experiment that would test females' responses to male fathering behaviors. What kinds of records would the experimenters have to keep? Be specific.
  4. If female sand gobies could lay only one or two eggs per year, how might their parenting change? How might the behavior of the males change? Give reasons for your answer.

For Educators

Sweden's Aquascope has pictures and facts about sand gobies. Click on "More Facts" at the bottom of the first page.

NOVA Online's Flying Casanovas explores courtship behavior in birds.


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