Another uncertainty involved in the MRL derivation is the use of 5% by weight as the default fat content in fish. Certain fish species have much more than 5% of fat in their body whereas some others contain much less (see, e.g., the data compiled by Gall, 2004). In other words, exactly how we should compare or equate the MRLs or similar tolerance limits from the two agencies (Codex and U.S. EPA) would also depend on what fish species are actually consumed (or to be consumed) in the locality of concern. It is of note that currently the literature tends to have a bias toward expressing the POC residues as per kg of muscle tissue in wet weight, rather than per kg of fat.