Fish Pick Up Tricks

Carnal Knowledge
Pretending to have a baby to score? Fish do it

By Faye Flam

Knight Ridder Newspapers

For our species and many others, fatherhood is sexy. According to one recent study, women are so attuned to fatherhood potential that they can tell whether a man likes kids by just looking at him. In other species, females won't give you a second glance if you're not already a devoted and prolific father.

For many fish, "being fatherly seems to be a strong signal to the female to mate," says Mark Sabaj, an ichthyologist at the Academy of Natural Sciences.

It poses a big catch-22 if you have to be a father to become a father. How can a guy break in?

In some species, such as sticklebacks, males will steal eggs from other males. In one type of minnow, says Sabaj, a male will oust a rival from his nest, treating most of the other guy's eggs as caviar but leaving behind just enough to fool a female into thinking he's a nice single dad.

Another popular tactic is fakery. This, Sabaj suspects, might explain one weird-looking catfish he's seen in various South American waters. Called a bristlenose pleco, the female looks normal enough but the male sprouts dozens of wormlike tentacles from his head.

Could the tentacles have evolved because females started mistaking them for fish larvae? A similar tactic almost worked for Hugh Grant's character when he borrowed a friend's child to help him score in the 2002 film, "About a Boy."

Other fish display fleshy yellow knobs or spots on their fins that look like eggs. So why not larvae? And the male bristlenose catfish is under pressure to look desirable since he has to be chosen by a female. Males stake out cavities in rocks and wait like eager young girls at a middle-school dance as the females swim by and inspect them. The females look for males tending larvae, or so they think.

Once she makes her choice, a female enters his cavity, lays eggs all over the walls, and leaves. This may not sound like hot sex by our standards, but to them, apparently, this is as good as it gets.

For all his trouble, once the male fertilizes the eggs and becomes a real father, he ends up with all the parenting and housework. "He uses his fins and mouth to clean the eggs and clear the cavity of detritus ... and aerates the clutch by fanning it with his pectoral fins," Sabaj wrote in a scientific paper co-authored with Jonathan Armbruster and Lawrence Page.

While a number of fish species put the parenting burden on the fathers, others dump everything on the mothers, Sabaj says, and in still others, nobody does anything but release sperm and eggs.