Quantification of the carbon released by a marine fish using a carbon release model and radiocarbon

Here we propose a carbon release model that divides fish-released carbon into two sources (ingested food and the fish body), and three forms (dissolved organic carbon (DOC), CO₂, and particulate carbon (PC)). We quantified the daily carbon budget of a marine fish Oryzias melastigma by feeding the fish radiocarbon-labeled living rotifer. We found that 91%-92%, 25%-47%, 28%-50%, 20%-31%, and 8%-9% of the ingested food carbon was absorbed, assimilated, and released as DOC, CO₂, and PC, respectively. Fish body carbon dissimilated/catabolized and released as 0.053-0.12 d^-1 at two daily food rations. DOC, CO₂, and PC accounted for 39%-42%, 39%-45%, and 16%-19% of the released fish body carbon, respectively. Our study shows that the fish transformed substantial fractions of their daily ingested food and dissimilated body carbon into DOC, and fish may be an important source of DOC in the ocean.