Studly Fish Aren't Born, They're Made—Sometimes Overnight

By Joseph Castro | July 18, 2011 4:16 pm

Some people like to say that men are always ready (and eager) for sex. Whether or not that’s true for humans, Stanford University researchers have recently learned that it is the case for certain male fish. Downtrodden male African cichlids, whose reproductive systems are so suppressed that biologists thought the fish couldn’t produce sperm, can successfully spawn within hours of rising to power, according to a new study published in the journal Proceedings of the Royal Society B.

Like many other animal species, a single leader—the biggest, baddest male—runs each group of African cichlids. This alpha male, which often sports vibrant blue scales, monopolizes the females and beats down other, weaker males in the community. (High school, anyone?) Because of this sexual exclusion, subordinate males suffer a noticeable pallor, decreased levels of reproductive hormones, and severely shrunken testes. Essentially, the fish trade sperm production for growth spurts, in hopes of someday overtaking the alpha male. Why waste energy making sperm if you can’t use it, right?

At least, that’s what lead author Jacqueline Kustan and her team thought. But when they took a closer look, they saw that the dominated cichlids generated no fewer sperm than the dominating cichlids, despite the fish’s physiological differences. Instead, the reduction in hormones and testes size only decreased the cichlids’ amount of motile sperm. So, they probably can’t have little baby fish if given the chance.

But then the researchers wondered: What would happen if a male cichlid’s social status suddenly shifted?

To find out, the Stanford team took two equally sized alpha males from two different communities and placed them together with three to four females. Within a day, one of the males had taken a submissive role and fled from the other male; after four weeks, it appeared to be physically and reproductively no different than a typical subordinate male.

The researchers then removed the alpha, giving the other male the opportunity to ascend the hierarchical ladder. But rather than the gradual changes the team expected to see, the liberated cichlid went alpha almost immediately, swimming protectively around its new territory and trying to entice the females. In just a few hours, it successfully spawned, and a day later it already developed the reproductive system of a seasoned alpha (with large testes to prove it).

It appears that the beta fish are just biding their time, producing sperm on the sly so that they can quickly take over when the opportunity arises, the researchers pointed out in a prepared video (above).

But is this really a smart move? If the fish are anything like baboons, being alpha male is quite a stressful job.

(via Physorg)

  • Geack

    Seems like starting with a fish that had been previously alpha needlessly confuses the issue. Any info avilable on why they didn’t just start with an already subordinate male? For now, based on the limited info in this article, it appears that all we know is that a previously alpha fish can get back to reproducing quickly, which doesn’t really match the claimed conclusions of the study.

  • Anonymous

    Many fish can breathe air via a variety of mechanisms. The skin of anguillid eels may absorb oxygen. The buccal cavity of the electric eel may breathe air. Catfish of the families Loricariidae, Callichthyidae, and Scoloplacidae absorb air through their digestive tracts


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