Abstract
Three different experiments were conducted to examine the oocyte development of the polychaete Hediste diversicolor in response to changing photoperiod and temperature at three different periods of oogenesis. In experiment I, worms collected during summer were reared under constant or decreasing photoperiod and temperatures to test the combined effects of the summer–autumn photoperiod and temperature transition on oogenesis. The result showed females collected during summer showed the highest oocyte growth when exposed to constant temperatures combined with decreasing photoperiod and decreasing temperature combined with constant photoperiod. In experiment II, worms collected in late autumn were under mimicked or shortened seasonal changes in photoperiod to evaluate the effect of accelerated change on oocyte growth. The result showed worms had 1.5 times faster oocyte growth rates when exposed to accelerated rate of change in photoperiod (2.5 times faster). In experiment III, worms collected in spring were exposed to different temperature regimes to examine the effect of raising temperature on the synchronization of oocyte growth and maturation. The results showed worms collected in spring showed increased temperatures will increase oocyte maturation synchronicity. It was concluded temperature and photoperiod transition can increase the oocyte development.
Highlights
The world’s aquaculture production has shown an annual growth of 8% over the last decades, and the sector is expected to continue to grow in the future (Food and Agriculture Organization [FAO], 2017)
To examine the effect of photoperiod and temperature on oogenesis, worms were exposed to two different light regimes [long days (LD), 16 h light, vs. short days (SD), 8 h light] and two different temperature regimes [constant temperature (T16), 16◦C, vs. gradually decreasing temperature (T16−7), from 16 to 7◦C]
The average growth in oocyte diameter was highest in worms reared at short photoperiod and constant temperature (SDT16, 0.76 μm·day−1), followed by worms reared at long photoperiod and decreasing temperature (LDT16−7, 0.66 μm·day−1)
Summary
The world’s aquaculture production has shown an annual growth of 8% over the last decades, and the sector is expected to continue to grow in the future (Food and Agriculture Organization [FAO], 2017). This sustainable growth demands alternative feeds and feed ingredients. Hediste diversicolor (Müller, 1776) (Nereididae, Polychaeta) is widely distributed from North Sea and Baltic Sea to Mediterranean They can obtain good growth rates and nutritional composition when fed cheap feed sources such as fish waste (Bischoff et al, 2009; Wang et al, 2019). To produce polychaete larvae year-round, closing and controlling the life cycle of the target species is paramount (Olive, 1999)
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