Snorkeling with Male, mouth-brooding Jawfish

Finally! The right place, right time…but wrong lens. Ah, the same old story, but I can fix that with a morning visit to locate my subject again. Would I find it? I had better, I have wanted this opportunity for a long time. The very next morning, I asked the resort to bring me back to the reef where I systematically covered as much ground as I could while still making sure I wouldn’t overlook him. There! There he is. A male dendritic jawfish (Opistognathus dendriticus) with hundreds of tiny eggs in his mouth!

Male seahorses, pipefishes, cardinalfishes, and jawfishes belong to a very unique club whose membership merely requires them to play the role traditionally assumed by the mother that of carrying fertilized eggs to term. Egg-carrying strategies that males employ include eggs that are kept inside brood pouches, eggs that may be attached to the underside of the belly, or eggs that are retained in the mouth.

Male cardinalfishes and jawfishes incubate their eggs by holding them in their mouths, a strategy called mouth brooding. Females lay an egg mass and after fertilizing them, the male takes the eggs into his mouth and incubates them for several days or up to several weeks for some species. During this time he does not eat, and his activities are restricted to juggling the eggs in his mouth to aerate them. Upon hatching, the juveniles usually remain in the same area as their parents, but receive no further parental care.

While the advantage of these strategies can be appreciated—providing a higher level of protection for their eggs during development—the reason for the males assuming the role of egg carrier is not well understood. It has been suggested that the female, who invested heavily in egg production, can now rest, which may result in the ability to reproduce more often. Given that they provide no parental care after birth and that few will survive, perhaps mating more often increases the chances that more of their offspring will survive.