Sydney: Cardinal fish can go to great lengths to protect their young. That means starving or even putting up with a jealous spouse - and often, dying young for their sake, a study reveals.
According to scientists from the ARC Centre of Excellence for Coral Reef Studies and James Cook University, the survival strategy that has served Cardinal fish so well for 50 million years could come unstuck due to rapid global warming.
"We studied how Cardinal fish has evolved over millions of years and found that these mouthbrooders haven`t changed much - their jaw cavities have become larger for keeping more young in their mouths, and their colours are different, but that`s about it," explained David Bellwood, professor and study co-author.
"While other fishes have evolved by changing shape and broadening their diet, the mouthbrooding fishes remain simple feeders that eat mainly plankton. This can be bad news when food is scarce," added Bellwood, the journal Proceedings of the Royal Society B reported.
With a lifespan of about two years, Cardinal fish breed several times a year, mostly in summer. Instead of laying thousands of eggs in a batch like other fish, they lay hundreds of slightly larger eggs, according to a university statement.
When the female releases the eggs, the male gathers them into a tight bundle which he keeps safe in his mouth for a couple of weeks until the young hatch and become free-swimming.
"These eggs occupy up to 100 percent of the oral cavity, and the dad`s mouth would expand and look like a large bubble," said Andrew Hoey, who conducted the study.
"It`s a wonder that they can even breathe. They don`t feed, but live on stored energy, and stay sedentary in and around corals," said Hoey.
"The females play the role of jealous wives. They stay close to the males, not to help rear the kids, but to prevent other females from swimming off with such a desirable mate. Our guess is these stay-at-home dads are very much in demand," Hoey said.
Although the 50 million-year-old breeding technique has proved successful so far, providing large and happy families for cardinal fishes, their future is looking grim, Bellwood said.
The other problem is the increasing lack of shelter as corals around the world die from bleaching and disease: Cardinal fish are popular prey for larger predatory fish like coral trout.