Carbonic anhydrase in some coral reef fishes: Adaptation to carbonate ingestion?

Abstract o 1. Carbonic anhydrase activity was measured in three species of coral reef fishes, Acanthurus triostegus, Holocentrus spinifer and Scarus jonesi. 2. Significant activity was found in extracts of blood, gill, gut contents, gut mucosa and bile. 3. Intestinal mucosa of the two calcium carbonate ingesting species was twelve times as active as that of the other species, which does not ingest carbonate. 4. In Scarus jonesi, significant differences exist in the intestinal mucosa activities of feeding vs fasted individuals. 5. Our data are consistent with the hypothesis that the ingestion of calcium carbonate may increase the CO 2 load and, therefore, necessitate high levels of gut carbonic anhdrase.