Aspects of the physiology of terrestrial life in amphibious fishes. III. The Chinese mudskipper Periophthalmus cantonensis.

The first paper of this series (Gordon et al. 1969) defined our usage of the phrase 'amphibious fishes', surveyed the literature on the physiology of terrestrial adaptations in those amphibious fishes lacking speciali2ed accessory respiratory organs, and presented data on aspects of related adaptations in the amphibious mudskipper fish, Periophthalmus sobrinus. The point was made in that paper that each species of amphibious fish appears to have adapted to terrestrial life in a different way. The present paper describes the results of a study of physiological adaptive responses shown by another amphibious fish, one phylogenetically quite distinct from all others previously studied. The Chilean clingfish Sicyases sanguineus belongs to the teleostean superorder Paracanthopterygii (Greenwood et al. 1966), which diverged from the other superorders of teleost fishes in the Cretaceous or Paleocene periods some 60-120 million years ago (Rosen & Patterson, 1969). S. sanguineus is one of the largest and most terrestrial of the clingfishes (Briggs, 1955). It occurs in large numbers intertidally and subtidally along rocky coastlines of western South America from southern Peru to southern Chile (de Buen, i960). Only limited physiological studies have been carried out on it previously, specifically aspects of respiratory metabolism and heart rate while out of water (Vargas & Concha, 1957; Concha & Vargas, 1957). We have studied the population living on the shore of Montemar, just north of Virla del Mar, Chile. Measurements made included survivaltime out of water, rates of evaporative water loss, upper lethal temperatures, three aspects of the 'diving syndrome' (metabolic rates, heart rates and blood lactic acid levels), and changes in nitrogen excretion. Ebeling, Bernal & Zuleta (1970) made related observations on behaviour in the field, aspects of the species' ecology, and aspects of respiratory physiology. Gordon (1970) discusses some of the implications of our studies of nitrogen excretion.