Gonad stage: Number of male or female clams in each of the following gonad stages: early mature; advanced maturity; mature; early regresion; final regresion. Classification was made after histological examination of alcohol-formol-acetic acid-preserved gonad samples. Tissue embedded in paraplast wax after dehydration, sectioned at 5 µm and stained with ARTETA trichromic stain before examination. Data points from Table 20.