This comes from this week's NY Times science section...
(
http://www.nytimes.com/2004/04/13/science/13OBSE.html)
JM
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It's pretty difficult (not to mention impolite) to talk with your mouth full. But the cardinalfish has a different problem. It finds it hard to breathe, as a full mouth impedes the flow of oxygen-bearing water past the gills.
Now, you may wonder just how often cardinalfish, found around coral reefs, actually become stuffed to the gills. The answer is quite often, though food has nothing to do with it. Like a few other types of fish, cardinalfish are mouthbrooders. Males keep fertilized eggs in their mouths for a week or two, until they hatch. Broods can be large, up to a quarter of the fish's body weight.
Researchers from the University of Oslo set out to determine what effect a mouth full of eggs has on cardinalfish respiration. They studied two species on the Great Barrier Reef off Australia, the fragile cardinalfish and the threadfin, using a laboratory setup that allowed them to measure respiration in various conditions.
The experiments, described in The Proceedings of the Royal Society: Biological Sciences, showed that a full mouth had little effect on fish at rest in water with normal levels of dissolved oxygen. But a mouthbrooding male has a reduced capacity for sustained swimming. And in poorly oxygenated, or hypoxic, water, mouthbrooding males of each species spat out their eggs to increase the flow of water to the gills.
The researchers found that the two species acted somewhat differently in response to hypoxia. Although the fragile and the threadfin are about the same size (three to five inches), the fragile has a larger average brood. Fragiles spat out their eggs at higher oxygen levels than did threadfins, and fragiles were incapable of increasing the pumping frequency of water past the gills to make up for reduced oxygen. The results, the researchers say, suggest a trade-off between brood size and the tolerance of low oxygen levels.
