The Environmental Science Graduate Students at Watlings Castle, San Salvador, Bahamas.(TME 98)
Parrotfish are very common throughout the reef systems of the Florida Keys and the Bahamas. They exhibit three unique adaptations that make them very interesting subjects for scientific exploration. Parrotfish have a set of pharyngeal teeth which are used to grind up corals. This adaptation helps them reduce interspecies competition for food resources within the reef community. A second adaptation that they exhibit is their hermaphroditic life style. This lets them change sex in response to fluctuations in population density. The third amazing characteristic of parrotfish is that at night they surround themselves in a mucous cocoon to protect them when they sleep.
Stoplight parrotfish, Sparisoma viride, belong to the Scaridae family in the order Perciformes. Originally over 300 different species were identified within the family, but further research showed that there were only 80 (Nelson, 1984). The parrotfish go through several color changes throughout their various life stages, which were confusing to earlier taxonomists. The stoplight parrotfish is also commonly named dark green parrotfish, moontail, parrot chub, and red belly (Bester, 2003).
Parrotfish have very large scales and a beak-like jaw with fused teeth. The teeth resemble a parrotŐs beak which is where they got their common name. Early observers thought they resembled the tropical bird when they where eating on the reefs. The pharyngeal teeth located in the throat consist of two convex plates that interlock with sets of molariform teeth to grind up hard corals after they are ingested. Their bodies are oblong and somewhat compressed with a rounded head and a characteristic row of scales on the cheek. They use their pectoral fins much like a birds wings to propel themselves through the water. For quick burst of speed they also use their caudal fins to escape predation, but they do not use the caudal fin as their primary source of propulsion like most fish.
Range and Habitat
These fish are commonly found in the tropical waters of the Caribbean Sea, Gulf of Mexico, and southern Florida and the Bahamas. They are commonly found around coral reefs in depths ranging from 3 to 50 meters. They are diurnal, feeding throughout the daylight hours and sleeping at night. At night they secrete a mucus cocoon for protection from predation. It masks them from being seen and it is beleved to keep their scent from reaching predators. Another advantage it gives them is its foul taste. Predators of parrotfish such as moray eels will not attack them when they are in the cocoon due to its taste.
Parrotfish feed primarily on algae and corals. They use strong beak-like teeth to scrape algae off of rocks and dead coral and also to bite off pieces of the hard living corals. The living coral polyps contain symbiotic algae known as zooxanthellae that provide the fish with nutrients. After a parrotfish ingests a piece of hard coral, it moves it to the back of the mouth to a specialized pharyngeal mill where the ratchet action of the pharyngeal teeth pulverizes it for digestion. Once the nutrients are removed from the coral, it is excreted back into the reef environment as fine white sand. Depending on its size, an individual parrotfish may produce up to a ton of sand per year.
The reproductive strategy observed in parrotfish is very unique among the fish community. They spawn all year, with an increased rate of reproduction during the summer months. Parrotfish and a few other reef species such as the wrasse family, Labridae, and the grouper family, Serranidae, take a hermaphroditic approach to reproduction. Parrotfish have two strategies that they use. In one strategy they are all born female and then later they can change sex into males. This strategy is known as protogynous hermaphroditism (Girlolamo, 1999). They can also begin life as males that are known as primary males. It is thought that the sex changes occur as a result of low population densities.
Another advantage is gained through this type of reproduction. In parrotfish populations, the large supermales, large males that were once female, are dominant. They claim most of the females, and the primary males often spawn in groups with one female (Warner, 1988). Starting out as a female and then changing sex later in their life histories is very advantageous. The females have no trouble finding mates no matter how large they are, while the males are much more reproductively successful as larger individuals (Warner, 1982). This lets the fish have a very successful life. They can reproduce as females when they are younger, and then when they grow to a large enough size to compete as males they change sex and reproduce as supermales.
Parrotfish exhibit sexual dichromatism throughout their lives, meaning that they are different colors depending on what life stage they are in. Primary males and females are often colored very similarly in dull reds, grays, browns, and blacks. They appear very boring in comparison to the secondary supermales. Supermales are often bright green, yellow, blue, red, and yellow (Nelson, 1984).
Age and Growth
Stoplight parrotfish can weigh up to 3.5 pounds and reach lengths of around 20 inches. Other Pacific Ocean species can grow to lengths in excess of 3 meters. They reach sexual maturity in the third year of life, and a typical life span for parrotfish is around 10 years.
Relationship with humans
Parrotfish are not a popular food in the United States except in Hawaii. In Hawaii, they were at one time very valuable. They were only to be touched by royalty. However, now they are eaten by everyone in Hawaii. As a food, they can sometimes cause nervous reactions to occur in humans that can even be fatal to a low percentage of consumers.
Throughout its evolutionary history parrotfish have undergone some amazing adaptations which make them very successful reef dwellers. They have found their niche or rather defined one for themselves through their reproductive strategies, eating habits, and their amazing protection mechanism. It is likely that these fish will continue to be successful for many years to come allowing that the coral reefs can be preserved and saved from human disturbance.
Bester, Cathleen. Biological profiles. Ichthyology, Florida Museum of Natural History, 2003.
The Columbia Electronic Encyclopedia, Columbia University Press. 2000. http://www.infoplease.com/ce6/sci/A0837716.html
Girlolamo, M. Social organization and sexual pattern in the Mediterranean parrotfish Sparisoma cretense. Marine Biology (1999) vol. 135, no. 2, pp. 353-360.
Nelson, Joseph S. Fishes of the World. 2nd ed. New York: John Wiley and Sons, 1984.
Warner, Robert. Sex change in fishes: hypotheses, evidence, and objections. Environmental Biology of Fishes. Vol. 22. No. 2 pp. 81-90. 1988.
Warner, Robert. Metamorphosis: Among tropical fish, when the going gets tough, the tough change sex. Science, Dec. 1982.
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