Complex sentence: Photoperiod also plays a role in smoltification regulation, whereby increased day length can accelerate smoltification, although temperature appears to limit this photoperiod control, as low temperatures prevent extended day lengths from accelerating the parr-smolt transformation.
Split into simpler sentences: Photoperiod also plays a role in smoltification regulation, whereby increased day length accelerates smoltification. Importantly however, temperature appears to limit this photoperiod control, with low temperatures preventing extended day lengths from accelerating the parr-smolt transformation.