2.1 Conceptual model
The conceptual model for the estimation of the carbon released from fish (Figure 1) is derived from the bioenergetics model for fish (Warren & Davis, 1967) and a carbon flow model for zooplankton (He & Wang, 2006). Theoretically, the carbon released from a fish can originate either from ingested food or from the fish body during short-term (e.g., daily) observations. Fish absorb carbon from ingested food; generally, most of the carbon in the ingested food will be released and lost through respiration, excretion and defecation, and only the carbon remaining is assimilated and used for fish growth or reproduction. Carbon in the fish body is renewed continuously, and the “old” carbon is released and is lost from the body. All the released carbon is released in the form of DOC, CO2, and PC. Therefore, the fish-released carbon derives from either ingested food or from the fish body and can be divided into the three forms, DOC, CO2, and PC.