Mouthbrooding Cardinalfish

How to photograph mouthbrooding behavior

Underwater photography of mouthbrooding Cardinalfish can be challenging and rewarding. On a recent visit to the Sabang Wrecks in Puerto Galera, Philippines, we found that a little patience can reward you with some interesting images of this unique marine life behavior.

Ringtailed Cardinalfish with eggs. 

Nikon D90, Nikon 105mmVR macro lens, ISO 200, 1/100th sec at f/16.

Understanding Behavior of Mouthbrooders

Like other Cardinalfish and several other types of fish, such as the Jawfish and many freshwater Cichlids, the Ringtailed Cardinalfish, Apogon aureus, is a mouthbrooder. Mouthbrooding occurs in several types of animals to include some frogs, but is most prevalent with fish. Infrequently it is the female or both sexes sharing the task of carrying the eggs during the incubation period, but usually, as is with Cardinalfish, it is the male alone who carries out these duties. Generally the female will release an egg mass close to the chosen male and after the male fertilizes the eggs, he will take them into his mouth to carry them during the incubation period, until the fry are ready to hatch. The male will generally be unable to eat during this incubation period. However, research in certain Cardinalfish species has shown that some males may show partial brood cannibalism, by eating up to 30% of it’s brood, during this period.

Male Cardinalfish rotating the egg mass

During this time the male Cardinalfish will open it’s mouth to rotate the egg mass on occasion, to keep the eggs clean and aerated. At times it will partially expel the eggs, during this process. It is this behavior, which is interesting to photograph. The egg mass starts out as a white bundle then turns a silvery color with the eyes of the fry becoming evident through the egg casing, towards the end of their development. To capture this behavior, it is best to use a longer macro lens, such as the 100mm or 105mm macro lens, to allow sufficient working distance for the fish to exhibit it’s natural behavior, without spooking it, yet still fill the frame. Every two to three minutes the pregnant male will open its jaw and rotate the egg mass before sucking it back into it’s mouth. You can spot the pregnant male by the extended pouch below its jaw.

Male Cardinalfish with extended throat pouch

Opening its mouth and showing eggs

Underwater Photography Tips for Mouthbrooders with Eggs

• During breeding season, the males have a pronounced buccal cavity or pouch below the jaw to hold the egg mass. Once you have spotted the males, look closely to find one that is carrying eggs. The larger the pouch, the more likely it is to be carrying eggs.
• When shooting with an SLR, use a longer focal length macro lens, such as a 100mm or 105mm macro lens, to allow more working distance. (See lens basics for more information)
• Find your subject and lock on to its location within the school. They usually do not move about too much, so it can be easy to focus on one subject for an extended period.
• Determine the proper settings to get the best exposure, prior to slowly moving in towards your subject, to prevent spooking them with too much movement. Use faster shutter speeds to capture the fast action.
• Keep your eye to the viewfinder and frequently refocus on your subject, when necessary and use the focus lock, to lock focus, to be able to take the shot quickly when the moment presents.
• Using a focus light can help to achieve faster focus.
• You may want to use burst or continuous release mode to get multiple exposures in rapid succession.
• Then it’s just a matter of waiting for that second or two when the moment presents and the fish releases the eggs from its mouth, to rotate and aerate the eggs, to capture the image.
• Remember… the moment only presents itself every 2 to 3 minutes, so it is important to have patience to be able to wait to get the shot.

Further Reading:

Mouthbrooder wikepedia article

Filial Cannibalism in the Paternal Mouthbrooding Cardinalfish

Sexual Difference in Buccal Morphology of the Paternal Mouthbrooding Cardinalfish

Guide to Anilao Diving for Underwater Photography

Ultimate underwater Critter List