Photo of the Week: April 19, 2010

Hi Gang!

This week’s POTW is from the reefs of Cozumel, an iconic tropical island destination located east of Mexico’s Yucatan peninsula. The photograph is of a species of angelfish commonly referred to as the queen angel or queen angelfish. Taxonomists know the species as Holacanthus ciliaris. 

I think divers from all parts of the experience spectrum agree that angelfishes are among the most eye-catching of all reef fishes. Their stunning colors, entertaining antics and the curious natures of many species make these fishes stand out in numerous tropical and sub-tropical reefs around the world.

Worldwide there are approximately 74 species of angelfishes. For many years angelfishes and butterflyfishes were described in the same family, but in more recent times ichthyologists have separated the two groups. Angelfishes are described in nine genera in the family Pomacanthidae while the world’s approximately 120 species of butterflyfishes are described in 10 genera in the family Chaetodontidae.  

Angelfishes are characterized by having a flattened, somewhat triangular, disc shaped-body, dramatically sloping forehead and mouth that is located on the front “end” of the face in what is known as the terminal position. Angelfishes also have a long spine at the base of their operculum, or gill cover. It is primarily the possession of this spine that caused taxonomists to separate angelfishes from butterflyfishes in the early 1970’s. 

Angelfishes are diurnal, meaning they typically swim about the reef during the day and retreat into the reef structure at night to rest. I remember shooting a film about the sea at night in the Bahamas some years ago, and during that film we documented the same queen angelfish resting at night in the same hole during every night of the shoot. 

The terminal mouth and long, tapering snout of angelfishes enables them to feed on a wide variety of small invertebrates that seek shelter in the crevices in reefs. A list of prey items includes a variety of algae, tunicates, anemones, zoanthids, hard corals, soft corals, hydroids, bryozoans and small crustaceans. Some angelfishes also readily prey upon sponges. Certain species only feed on a single sponge species, while others are widely indiscriminate.

In addition, some angelfishes also serve as cleaner species as they have an appetite for parasites that pester other reef fishes.  It is widely accepted among specialists that the bright coloring of many juvenile angelfishes serves to advertise their presence as available cleaners. Some juvenile angelfishes are also known to feed on the mucus coatings of squirrelfishes, soldierfishes, cardinalfishes and other reef species.

The sexes in angelfishes are separate with males tending to be slightly larger than females. Juveniles are often highly territorial, and are often seen chasing fishes that intrude into their realm. The trait of territoriality is not part of the life style of the adults. In most species the juveniles are brightly colored and many display eye-catching patterns with the colors and color patterns commonly being very different than those of the adults of the same species. The colors and patterns change as the fishes approach sexual maturity, an adaptation that helps interested adults identify potential mating partners.

Spawning occurs throughout the year with most of the reproductive activity taking place shortly after sunset. Interestingly, adults of many of the physically larger species of angelfishes form strong male/female pair bonds, while many of the smaller species form organized harem groups. A harem usually consists of one male and two to five females with the male being the dominant fish. If he is eliminated from the social group, then the dominant female will gradually transform into a sexually functioning male over a period of several weeks.

In harems, when the fishes spawn the male and females congregate at the edge of the reef where a female flits towards the surface releasing her eggs as she goes. The male is quick to follow her and fertilize the eggs she has released. The male spawns with each of the females in the harem with the entire affair lasting no more than a few minutes. Females produce between 25,000 and 75,000 eggs each evening with upwards of 10,000,000 being produced over the course of a spawning season. Each egg contains a single drop of oil, and that is enough to make the eggs positively buoyant causing them to rise toward the surface where they will remain until the embryo fully develops and hatches. The incubation period is very brief, lasting only the 12 to 24 hours it takes until the eggs hatch and the larvae enter the water column in their planktonic form. With species of larger angelfishes that reproduce in mated pairs, the male will pursue his mate around the reef with most of the rest of the details being similar to those found in the harem groups. 

The queen angelfish ranges throughout the Bahamas and Caribbean, and from Florida out to Bermuda, south to Brazil, and east through the Gulf of Mexico. They are usually found in coral reef communities at depths between 20 and 70 feet. Queen angelfish are often shy and seem somewhat wary around divers, but every now and then one will show a high degree of curiosity and swim right up to divers. No doubt, their handsome appearance makes them irresistible to underwater photographers.

I hope you enjoy this week’s POTW!

See you next week,

Marty