Influence of temperature and photoperiod on ovarian development and spawning of smallmouth bass (Micropterus dolomieui)

The reproductive cycle of smallmouth bass (Micropterus dolomieui) from the 45° 14'N latitude and 71°58'W longitude has been investigated with regards to constant temperature-photoperiod regimes, seasonal and protracted cycles over two years. The morphology and the histology of the ovary, the changes in plasmatic components and the uni-multi-spawning capacity were followed to verify the influence of temperature and photoperiod regimes, and the plasticity of smallmouth bass reported as eurytopic. Results showed individual variability of ovarian development partially related to the desynchronizing effects of constant conditions and a group-synchronous ovary with a possible asynchronous ovarian development under constant conditions. A positive correlation between plasma calcium and the presence of vitellogenic oocytes was also noted. Plasma protein, calcium and oestradiol-17p levels increased with vitellogenic activity. The presence of atresia was associated with the maintenance of vitellogenic activity over long periods particularly under constant winter conditions. Oocytes did not mature under a second year of constant summer conditions. Smallmouth bass showed a capacity of spawning one to four times a year at 15-30 day intervals. Fecundity and nest productivity were highly variable (500-18,000 oocytes and 0-8,500 eggs released, respectively) but within the range of previous studies. The study delineated the proximate and ultimate controls of temperature on ovarian maturation and spawning regardless of the photoperiod regime. Photoperiod was not shown to have any direct effect on the reproductive cycle. Controlled temperature-photoperiod conditions can induce spawning in any month of the year. Temperature was the decisive factor in the ovarian development and the spawning of smallmouth bass, as it has been shown to be for other teleosts. Sequential sampling of fish demonstrated individual and seasonal variations of ovarian development and synchronization. Furthermore, fish can modulate their spawning tactics based on environmental conditions