The degeneration of postovulatory follicles (POFs) in time and at different temperatures was studied for the Bay of Biscay anchovy. For this purpose a key of 7 POF stages, solely defined on the basis of their histological degeneration characteristics, was applied. The novelty of this procedure is that it separates staging of POFs from their ageing process. The female gonads, taken from several captivity experiments and field samples, were classified in this way. Water temperature in captivity tanks corresponded to high values (17-21°C), except for one case in which different day and night temperatures were applied. In addition, 472 field samples (11948 anchovy females) from several cruises were examined; of these, 126 samples (3348 females) were identified as coming from areas of high sea surface temperature (weighted mean =17.76°C, s.d.=0.84) and 131 samples (3181 females) as coming from areas of low sea surface temperature (weighted mean =14.42°C, s.d.=0.75). There was close agreement in the succession of POF stages over time after spawning between the experiment and the field samples. The first four stages of POF degeneration occurred in less than 24 h, and by the end of the first day the POFs were mainly in Stage V. Stages VI and VII showed their highest occurrence during the first and second half of the second day after spawning, respectively. Full resorption of POFs was achieved in about 55-60 h. For the range of temperatures examined (13-19°C), little effect of temperature on the degeneration of POFs over time was noticed. The advanced degeneration stages were found all day round, showing some overlapping periods when successive spawning cohorts co-occurred. The application of these results for ageing POFs is discussed.