Revision of criteria for the classification of postovulatory follicles degeneration, for the Bay of Biscay anchovy (Engraulis encrasicolus L.)

This study proposes a detailed histological key for the examination of the postovulatory follicle’s (POF’s) degeneration for the Bay of Biscay anchovy (Engraulis encrasicolus). Such key was established uniquely on the basis of histological features not regarding to the time of capture of the samples. The objective of this procedure is to overcome the difficulties associated to the estimation of the Spawning Frequency on the basis of the determination of POF’s degeneration stages that have been traditionally divided into three great stages corresponding to daily spawning cohorts. The 7 stages presently proposed suppose a better differentiation and resolution of the different phases of POF’s degeneration. This fact allows separating the staging of POF’s from that of ageing. In that way, samples obtained at any time throughout the day can be used and not only those sampled during a discrete period of the day.