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The weight of sand, coral scrapings, algal fragments, and other calcareous materials which pass through the intestines of reef fishes was calculated on a hectare-per-year basis. It was found that browsing omnivorous reef fishes which rely, in part, on a plant diet ingested and redeposited at least 2300 kg of such material on a 1-hectare study reef near Bermuda. Reasons are presented why this estimate, certainly in order of magnitude, should be applicable to coral reefs in general.

Studies of behavior in yellow bullheads showed that they recognized individuals of their own species by means of pheromones. After training by reward and punishment, blinded bullheads were able to discriminate between the odors of two donor fish, but they lost this ability when deprived of their sense of smell. The main source of the intraspecific chemical stimuli involved in recognition is the mucus. A change in status after fighting was chemically communicated to other bullheads.

Fish of the genus Ictalurus can find distant chemical clues by means of taste alone, and they exhibit true gradient searching in the absence of a current. Neither unilateral nor bilateral deprivation of the sense of smell impaired their searching ability, but unilateral deprivation of taste receptors which are spread over body and barbels of the animals caused pro nounced circling toward the intact side. The relation of swimming paths of the fish to the chemical in the water suggested that comparisons of concentrations were made in time and space.

Two types of detergents, one easily oxidized and the other not, damage the chemoreceptors of yellow bullheads, Ictalurus natalis (le Sueur) exposed to concentrations of 0.5 parts per million in the surrounding water. This concentration is considerably lower than that at which sublethal damage has been detected previously. Histological examination reveals erosion of the taste buds; electrophysiological methods and observations of swimming and feeding behavior reveal impairment of receptor function. Affected fish do not fully recover after 6 weeks in detergent-free water.