Feeding ecology and diet

Surfperches feed variously on shrimps, amphipods, crabs, and other crustaceans, as well as mollusks and worms. To feed on such organisms, many surfperches take indiscriminate bites out of the algae and debris found on the bottom, and then winnow out their invertebrate prey within the oropharyngeal cavity, spitting out the remainder. The small kelp perch (Brachyistius frenatus) feeds largely on ectoparasites picked off other fishes, and several other surfperches supplement their regular diets by engaging in such cleaning activities.

Cichlid feeding ecologies are extravagantly diverse, and may partly explain the species diversity within the family. Although most cichlids can opportunistically feed on a wide range of foods, they are also specialized to feed on certain types of food with particular efficiency. Of course, many cich-lids specialize in hunting other fishes and eating them whole. Tilapia is the only genus of African cichlid to specialize on phytoplankton, by collecting the particles (with the assistance of sievelike gill rakers for filtering) in balls of mucous secreted in the mouth and then swallowing them. Deposit feeders take a very similar approach, but with sedimented phyto-plankton and even disintegrated hippopotamus droppings. Cichlids who feed on epilithic algae, or aufwuchs, scrape the algae from rocks, typically employing multiple rows of fine teeth used like a file. Periphyton feeders scrape algae off living plants. For example, the giant haplochromis Hemitilapia

Cyathopharynx Furcifer

Breeding habits of the cichlid Cyathopharynx furcifer 1. Male drags long pelvic fins along the bed of the nest, showing female where to lay eggs; 2. Female lays eggs while male waits to fertilize them; 3. Female takes fertilized eggs into her mouth; 4. Hatched fry are released from the female's mouth. (Illustration by Gillian Harris)

Breeding habits of the cichlid Cyathopharynx furcifer 1. Male drags long pelvic fins along the bed of the nest, showing female where to lay eggs; 2. Female lays eggs while male waits to fertilize them; 3. Female takes fertilized eggs into her mouth; 4. Hatched fry are released from the female's mouth. (Illustration by Gillian Harris)

oxyrhynchus in Malawi feeds by placing the grasslike leaves of the plant Vallisneria between its jaws and nibbling off the algae without damaging the leaf. Singularly robust dentition characterizes leaf choppers, while mollusk feeders have large pharyngeal bones covered with flat, stocky teeth to crush shells. Labidochromis vellicans of Malawi, a benthic arthropod feeder, has very long, sharp, outward pointing teeth that resemble forceps, and uses them to pluck insects from the substrate. Alternatively, the greenface sandsifter (Lethrinops furcifer) of Malawi has a pointed, protractile mouth and sievelike gill rakers. It rams its head into the sand, filling the buccal cavity, then separates out and swal lows insect larvae by expelling the sand across the gill rakers and through its opercular openings. Some species have developed protractile mouths specially suited for inhalant feeding on zooplankton. There exist fin-nipping feeders, and in Victoria and Malawi, species that feed on the eggs and larvae of other mouth brooders. Many species have acquired large molariform teeth on the pharyngeal jaws for crushing the shells of snails. Additionally, in all three African Great Lakes, cichlids with differing tooth morphologies have evolved to feed exclusively on the scales of other fishes; some even mimic the color patterns of their prey to avoid detection.

Interesting selective forces are at work within the scale-feeding Lake Tanganyika genus Perissodus. To a greater or lesser degree, all seven species exhibit laterally asymmetrical mouths that are angled either to the right or left, and this trait has a genetic basis. Left-handed individuals nip scales off the right flank of their prey, and vice versa for right-handed individuals. Incredibly, the differential alertness of prey species appears to exert selective pressure on the scale eaters that acts to maintain about equal numbers of left- and right-handed individuals within a population. A study on Perissodus microlepis found that whenever one or the other form becomes significantly less abundant, prey species become more vigilant about watching for scale eaters from the side favored by the more abundant form. In this way, the less-abundant form is conferred a selective advantage, and the genetic polymorphism responsible for the two forms is maintained.

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