What the Fish? Episode 4: Sneaker Males Are My Anemone

To milt or not to milt?

For most fishes, reproduction involves eggs and milting, which is like crop-dusting with sex cells (aka gametes). The vast majority of fishes are oviparous, which means they lay eggs that are fertilized and develop outside the mother's body. In these situations, males typically milt, which is the release and spreading of their gametes, onto the eggs that have been deposited in the environment. In ovoviviparous fishes, the eggs develop inside the body of the mother, and male gametes have to be passed into the females’ body through specialized structures, such as claspers (modified pelvic fins) in sharks or gonopodiums (modified anal fins) in guppies. Live birth (viviparity) has also evolved in a number of lineages of fishes, including sharks, guppies, and rockfishes. In viviparous fishes, the young develop within the mothers’ body.

Male, female, or both?

While most fishes have separate sexes, a number of lineages are simultaneous or sex-switching hermaphrodites. Some fishes, such as clownfishes, can change their sex once during their lifetimes either from female to male, or male to female depending on environmental and/or behavior scenarios. A small number of fish species are simultaneous hermaphrodites capable of producing both male and female gametes at the same time (e.g., lancetfish, some species of moray eels as seen above). Scientific studies have identified that at least some of these species (e.g., the mangrove killifish Kryptolebias marmoratus) are capable of self-fertilization!

Fish of the Week: Orange Clownfish (Amphiprion percula)

Family: Pomacentridae

Distribution: Western Pacific

Maximum Size: 11 cm

Fun Fact: Clownfishes are all born as males, with some males changing their sex to female over the course of their lives.

Encyclopedia of Life: Orange Clownfish

The orange clownfish lives in shallow lagoons and reef systems, and it is frequently found in symbiosis with species of anemones in the genus Heteractis. Clownfishes acclimate to the stinging tentacles of anemones by mixing the slime of the anemone with the slime of its own skin. They live in a social hierarchy-based system composed of a large reproductively active female, smaller reproductively active males, and even smaller males that are not permitted to breed through the hierarchy. If something happens to the female, the largest male will change sex and become the new reproductively active female, with a smaller male moving up the ranks to become a reproductively active male.


You can follow us on Twitter and tweet us your fishy questions @FM_WhatTheFish or email us at whatthefish@fieldmuseum.org.

So long, and thanks for all the fish!

Fish Nerds Podcast Team:

Beth Sanzenbacher

Eric Ahlgren

Leo Smith

Matthew P. Davis

DNA Discovery Center