Description d'une frayere et comportement de reproduction de la grande alose (Alosa alosa L.) dans le cours superieur de la Loire

National audienc

Description d'une frayère et comportement de reproduction de la grande Alose (Alosa alosa L.) dans le cours supérieur de la Loire

Une frayère de grande Alose (Alosa alosa L.) a été décrite dans le cours supérieur de la Loire et le comportement de reproduction des adultes a été observé durant toute la période de frai en 1988. Le site était caractérisé par la présence d'un épi et par l'abondance de matériaux fins dans le substrat (sables et graviers). La reproduction était essentiellement nocturne avec un pic d'intensité très net au milieu de la nuit. L'activité de frai a été reliée négativement à la valeur journalière du débit d'eau et ne semble pas être influencée par la température de l'eau. Le nombre de géniteurs a été estimé à environ 34.200 individus. Les résultats montrent que : (1 ) cette frayère devait être un site de reproduction forcée et non typique de la grande Alose, et (2) apparaissait comme une des plus importantes observées sur les grands fleuves français

Primary and secondary oocyte growth dynamics in anadromous semelparous allis shad Alosa alosa

We analysed the ovarian dynamics of the anadromous semelparous allis shad Alosa alosa for which our working hypothesis was that mature pre‐spawning females would have very low or even exhausted primary growth (PG) oocyte reserves; semelparity has been linked with the depletion of the pool of PG oocytes. To test this hypothesis, the PG oocytes were enumerated, their recruitment pattern to the secondary growth (SG) phase was analysed and their potential replenishment from the pool of oogonia was examined in females caught very close to the Mondego River mouth, in central Portugal and along the river. The development of the SG oocytes was also analysed, the fecundity (batch, total and annual) values were estimated and the intensity of atresia was quantified. Ovarian samples and histological sections were investigated in parallel. A dynamic recruitment pattern of PG oocytes to the SG phase was revealed, where all PG oocytes were recruited and were not replenished by oogonia. Annual fecundity was subject to down‐regulation due to atresia prior to spawning and its size was multiple times higher than the size of batch fecundity. Lack of population synchronicity in ovarian development and spawning migration was also observed. This multifaceted analysis of the ovarian dynamics of this species will contribute to management efforts for this critically endangered and economically important fish throughout its geographical distribution. The results reported in this study will also assist in unravelling the complexity of the early processes of oogenesis in fish

An unexpected host for the endangered giant freshwater pearl mussel Margaritifera auricularia (Spengler, 1793) as a conservation tool

International audienc