Red-hot Monkey Sex: Reproduction in the Wild Pt. 1, the Goldfish

I love my job. I’m not a mattress tester or an ice cream taster. I don’t zip from peak to valley in a wingsuit or advise heads of state. Nope. I study behavioral neuroscience. Social behavior is my passion and, although spending hours watching goldfish–my model organism–might seem like a snooze, I’m smitten. Goldfish are a hard sell, but stifle your yawns: their reproductive behavior is fascinating.

First off, like many fish species, the goldfish relies on external fertilization to get the job done. No hanky-panky, hardly any touching…and NO snuggling afterwards, either. Sounds like hell, right? But how can the goldfish reproduce without physical contact? Instead of  P(or equivalent)IV(or equivalent), males release their sperm into the water near a female, who in turn releases her eggs. Look elsewhere for passionate embraces, but external fertilization isn’t the end of the story.

Foreplay isn’t optional for the goldfish. (Suddenly envious?) In order for males and females to come into reproductive condition, environmental factors and pheromonal cues have to coincide. Environmental factors don’t include Glory Box by Portishead, rose petals, or mood lighting. But don’t despair yet: there is some romance to goldfish sex. Reproduction is preceded by an intricate, cooperative phermonal dance between the sexes. Female phermones stimulate the production of sperm in males, while phermonal signals from rival males can inhibit sperm production.

But that’s just the preamble. Sure, the foreplay’s pretty neat, and the external fertilization is fascinatingly alien, but the goldfish’s social system is the star attraction. In many vertebrate social groups, hierarchies are established among the sexes: there’s a dominant male and, often, a dominant female. This exceptionally smug male will sire (almost) all of the group’s offspring. (Think silverback male gorilla.) Dominance in these social groups is a measure of genetic fitness; if only the dominant male reproduces, the logic goes, the group’s offspring will have his champion genes. And while champion genes are well and good, an established social hierarchy whittles away at genetic variety. But the goldfish–the clever, clever goldfish–has a solution that adds variety AND keeps those champion genes in circulation.

Male goldfish do compete against each other for access to females’ eggs, but competition occurs only when a female is ready to release her eggs. These displays–called “scramble competitions”–are brief and, usually, relatively nonviolent. Scramble competitions are all about location, location, location: a limited number of positions proximal to the female’s genital papilla/vent region are conducive to fertilization. The enterprising male goldfish makes like a bumper car and shoves, weaves, and nudges his way to victory. Because males’ reproductive fitness is so susceptible to the influence of external factors, the male who “wins” the female varies with each mating. A fit male comes out on top, sure, but WHICH fit male isn’t predetermined. Multiple fit sires keep the gene pool diverse and the offspring healthy. What a clever system, right?

A male goldfish in pursuit of a female will nudge her vent area to stimulate the release of eggs.

And that’s where the story ends. It’s over after a night of passion. Goldfish are the ultimate permissive parents: no curfew, no regurgitating insects, no defending a burrow, no paying for 4+ years of higher education. Wham, bam…over and done. Instead, (relatively) nonviolent reproductive competition is where the goldfish shines.

(In the wild, females conceal their eggs by releasing them near water plants; in captivity, where plants aren’t always available, females have been known to spawn in loose yarn or…mops. If you feel like surprising your partner with a spawning mop (and I guarantee that she/he/they will be very surprised), you can find DIYing instructions at


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