Effects of Three Cold Weather Event Simulations on Early Life Stages of Southern Flounder Paralichthys lethostigma

The objective of this study was to determine what life stages of cultured southern flounder could tolerate differing levels of cold weather event simulations.  Evidence suggests that low temperatures (< 12°C) are detrimental to premetamorphic larvae, thus increasing the vulnerability of this species held in outdoor grow out ponds.  Information is needed to identify the smallest/youngest size class that could successfully survive within these ponds during a cold weather event.  We examined two distinct life stages: premetamorphic larvae, and postmetamorphic juveniles of the postmetamorphic juveniles we were able to examine two size classes (small/recently-morphed = 9.8 ± 0.3 mm in TL and large = 19.7 ± 0.6 mm).  Life stages were subjected to a simulation dropping temperatures (-0.33°C/h) to one of three goal temperatures (4, 7, or 10°C) and then increasing temperatures (+0.33°C/h) to original start temperature.  Fish were fed and monitored daily for survival.  This study found that large postmetamorphic flounder had good survival for all temperature treatments (89 – 100% survival), whereas both premetamorphic larvae and small postmetamorphic juveniles had low survival (< 30%) for all temperature treatments.