A simple method for collecting 14CO2 in fish.

A simple apparatus was designed for continuous collection of excreted 14CO2 in fish. Carp (Cyprinus carpio; body wt. about 400 g) were intraarterially injected with [14C]acetate (44 mmol) and transferred to a test chamber (21 +/- 1 degrees C). Within 48 h, 65.4 +/- 2.7% of the dose was recovered as 14CO2. A small amount of 14CO2 was retained in the water of the test chamber. Control experiments using [14C]acetate-injected mice as '14CO2-generators' showed that this 14C residue in the water could be recovered almost completely as 14CO2 upon acidification. In the carp experiments, some radioactivity remained in the acidified test chamber water; this residue may represent unchanged [14C]acetate and/or metabolites other than 14CO2.