This document specifies a laboratory test method for screening anti-fouling paints in a flow-through system using mussels as the test organism. It is intended to be used in conjunction with ISO 21716-1, which specifies the general requirements. The purpose of the test is to determine if there is a difference in mussel settlement on painted test panels compared with mussel settlement on inert non-toxic control panels under the conditions of the test. Examples of statistical analysis to determine if the difference in mussel settlement is statistically significant are given in Annex A.