REPRODUCTIVE-BIOLOGY AND FECUNDITY OF THE BAY OF BISCAY ANCHOVY POPULATION (ENGRAULIS-ENCRASICOLUS L)

This review presents the results of field studies conducted between 19 87 and 1992 on the on reproductive biology and fecundity of the Bay of Biscay anchovy. Close to 100% of the anchovy population reach maturit y during the reproductive season, although the smallest 1-year-old anc hovy mature slightly later. At peak spawning, however, the reproductiv e output (numbers of eggs laid daily per unit body weight) of one year oil anchovy is similar to that of older anchovy. Anchovy mainly spawn from 19:00 to 6:00 (GMT) with a peak at 00:00 (GMT). For the females spawning on a given night, the final maturation process of the spawnin g batch of oocytes starts the night before. The process of nuclear mig ration proceeds through the night and the first parr of the following day. Oocytes start to hydrate early in the afternoon of the day of spa wning. Hydration reaches its maximum intensity at dusk and in the earl y night. Gonads with postovulatory follicles can already be observed b efore dusk, indicating the start of spawning activities. Anchovy is a batch spawner with indeterminate fecundity. 'De novo' vitelogenesis pr oceeds in immature oocytes during the reproductive season. Annual fecu ndity is determined by both the number of eggs laid per spawning (batc h fecundity) and the number of spawnings per season (frequency of spaw ning and duration of the spawning season). Batch fecundity presents al increasing pattern as the season advances, from ca. 200 eggs/g in Apr il, to ca. 500 and ca. 650 eggs/g in May and June respectively. The fr action of females spawning per day ranges from 18 to 33%, and increase s as the season progresses. This high spawning frequency may be relate d to the relatively short spawning season. Assuming a two month protra cted spawning season, the total reproductive output of Bay of Biscay a nchovy can range between ca 9,000 to ca. 11,000 eggs per unit gonad-fr ee body weight (g).