Stuffed

Natural History, July-August, 2004 by Stephan Reebs

Few species of fish take care of their young, but the dedication among the ones that do can reach heroic levels. Consider the cardinalfish. Once the male has fertilized a clutch of eggs, he carries them in his mouth for one to two weeks, until they hatch. But because the clutch is so large (as many as 2,000 eggs), his mouth is so full he can't eat--except for snacking on the occasional egg.

A fish has his limits, though. Sara Ostlund-Nilsson and G6ran E. Nilsson, both biologists at the University of Oslo in Norway, caught males of two species of cardinalfish native to Australia's Great Barrier Reef and monitored their responses to decreasing concentrations of dissolved oxygen (a situation found in some recesses of a coral reef). When the oxygen dropped to about a third of the normal level, boom! the incipient dads started spitting out their broods. Dads of the species whose broods are relatively large (as a fraction of the male's weight) were the first to spit out their eggs. Having a big family may sound like a good insurance plan, but plans can falter when times get tough. ("Breathing with a mouth full of eggs: Respiratory consequences of mouthbrooding in cardinalfish," Proceedings of the Royal Society of London B 271:1015-22, May 22, 2004)--S.R.