Labridae Fishes: Morphology, Feeding Habits and Limitations

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The family Labridae, otherwise known as wrasses, is marine fish consisting of more than 575 species found in warm-temperate and tropical reefs around the globe (Wainwright et al. 2004). Of all of the coral reef fishes worldwide, the family Labridae is one of the most morphologically diverse (Westneat 1995). Due to their different morphologies, different fishes within the species prey on different types of food. The main difference making up the separate morphologies, and subsequently feeding habits, is the functional and mechanical properties of the jaw. Due to so many variations of the functional morphologies of feeding, many studies have been conducted on wrasse feeding behavior to distinguish how the different modifications of morphology have become so diversified using the same basic mechanical (jaw) feeding system (Wainwright 1988; Westneat 1995; Hulsey and Wainwright 2002; Bshary 2003; Wainwright et al. 2004). All various species within the Labridae family vary in their food preferences and specializations. Prey includes coral, shrimp, fish, hard-bodied prey, soft-bodied prey, parasites, and algae. The highly specialized nature of the feeding behavior of the wrasses is responsible for their occupation of very narrow ecological niches.

In particular, we observed the genus Halichoeres in Belize, which includes the Yellowhead Wrasse, Halichoeres garnoti, as well as the Bluehead Wrasse, Thalassoma bifasciatum. This species demonstrates forceful and crushing feeding patterns. This type of feeding is derived from the morphology of its pharyngeal jaw. The jaw of Halichoeres has two muscles originating at the neurocranium extending downward and inserted into the lower pharyngeal jaw, without any joints (Wainwright 1988). Although these jaws offer extreme crushing force, the force is dependent upon many variables including the crushing force potential, the pharyngeal jaw gape, and the body length. These three factors designate whether the Halichoeres eat hard prey or soft prey (Westneat 1995).. There is a distinct, positive correlation between the body length and the crushing force potential (Westneat 1995). In a study by Wainwright, he observed various Caribbean wrasses, their feeding behavior and linked them to their individual morphologies (Wainwright 1988). The species Halichores. maculopinna, also known as the Clown Wrasse, has the lowest pharyngeal jaw strength. This species also has the smallest body length but largest jaw width, which allows for a diet consisting mainly of phytoplankton and zooplankton. Increasing moderately in body length and pharyngeal jaw strength, Halichores bivittatus (Slippery Dick) and H. garnoti (Yellowhead Wrasse) have diets consisting of both hard and soft shelled diets, but hard prey contributes less to the diet than soft. The largest species with the greatest crushing force potential, H. radiatus, the Puddingwife wrasse, has a diet consisting of considerable amounts of hard-body prey, with crabs being a major dietary component (Wainwright 1988). Field observations made at South Water Caye, Belize, showed H. garnoti exhibit a type of grazing behavior that supports the relationship between pharyngeal jaw strength and crushing potential, as observed by Wainwright’s experiment. The body length of the Yellowhead Wrasse is approximately 17-18 cm, an intermediate size compared to the smaller Caribbean Cleaner Wrasse or the larger Puddingwife Wrasse. I observed a few different Yellowhead Wrasses and each of them displayed the same behavior: they would cruise around in shallower reef zones, about 0.6-0.9 m. above the ocean floor, circling an area about 9.1-12.2 m., occasionally diving into a crevice of coral or biting at the coral. When they went into the coral crevice, although I could not see what they were eating, I am assuming they found small crustaceans, snails, shrimps or worms. I did not observe how they disposed of the food waste, such as the crushed up shells....
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