Warming delays ovarian development in a capital breeder

The consequences of rising temperature to reproductive development in the lesser sandeel, Ammodytes marinus, were studied in captive fish held at three temperatures to reflect the present day and future predicted winter temperature of North Sea habitat. Our results showed that an increase in temperature of 5 °C led to more than a 2 month delay in the timing of oocyte maturation. The inverse relationship between the stage of ovarian development and temperature in A. marinus is in contrast with that seen in many early year spawners. A close relationship between relative ovary size and ovarian development, as well as an overlap in oocyte diameter among treatments suggested that this temperature effect is mediated via an energetic constraint on reproductive investment. Temperature had no effect on the potential fecundity—length relationship in December, and while the intensity of pre-ovulatory atresia did not reflect condition, it was found to increase with temperature and decrease with oocyte diameter. The magnitude of potential temperature-related changes in spawning phenology could have important implications to the future match between hatching times of A. marinus and prey availability, although this may be partially mitigated by the positive temperature dependence of embryonic development.