Cardinalfish

Cardinalfish 
Cardinal fish inhabit the Atlantic, Pacific and Indian oceans. While primarily saltwater fish, some species do live in brackish and freshwater. They are ray-finned, nocturnal fish who generally feed on zooplankton and some small invertebrates. Though cardinal fish in captivity are smaller than those in the wild, they make colorful, easygoing pets.

Some fish species protect their eggs and young from predators with an oral incubation technique. In many cases, the male takes on this responsibility, fertilizing the eggs and then holding them in his mouth for the duration of gestation. While cardinal fish incubate their fry only up to this point, some fish species protect their offspring beyond birth.

Mouth brooding gives the male parent a close watch on the egg mass and helps to provide an extra layer of protection, ensuring they survive and develop into fit, self-sufficient offspring. Rotating and expelling them occasionally helps with air circulation and cleanliness.

Species that mouth-brood after eggs hatch are able to let their offspring out for feeding and swimming. When they suspect danger, the parent may use behavioral cues to recall the young ones. However, for the parent, mouthbrooding does have negative effects on feeding; he may be unable to eat during the brooding period. Left underweight, cannibalism sometimes occurs with the male cardinal fish digesting up to 30 percent of offspring.

Reference:
http://en.wikipedia.org/wiki/Mouthbrooder
Photo credit : Nicholas Terry
More of his work:
http://www.flickr.com/photos/16692936@N07/