Effects of Photoperiod and Substrate on Larval Development and Substrate Preference of Juvenile Southern Flounder, Paralichthys lethostigma

ABSTRACT

During the last decade, decreased landings of flounder along the mid- and south Atlantic coast have stimulated interest in flatfish aquaculture. The euryhaline southern flounder, Paralichthys lethostigma, is tolerant of great salinity and temperature ranges, making it a good aquaculture candidate. A 54-day study was undertaken to investigate the effects of photoperiod and substrate type on survival and growth of larvae and on pigmentation of recently metamorphosed juveniles. Photoperiod treatments consisted of continuous light, which is the current practice in flatfish aquaculture; 10 hours of light, which mimics the natural photoperiod; and continual darkness, to examine effects on visual feeding. Substrate treatments consisted of either no sand (bare, black fiberglass tanks) or sand-covered tank bottoms. All fish in the continual darkness treatment died within 18 days of hatching. Photoperiod and substrate type significantly affected survival. Survival was higher in the 10 hours of light treatment than in the 24 hours of light treatment (24% vs. 12%, respectively) and in the no sand treatment compared to the sand treatment (13% vs. 4%, respectively). There was no difference in mean total length of metamorphosed juveniles. There were no treatment effects on the percent normally pigmented juveniles. A study examining substrate preference indicated that small juveniles preferred mud and sand substrates over black or white bare tank bottoms. It was also shown that juveniles can readily adapt to a dark substrate. However, adaptation to a tan-colored sand background required a long time period, and some fish were not able to adapt, even after 19 days of exposure.

Key Words:

• Southern flounder
• Paralichthys lethostigma
• larvae
• photoperiod
• substrate
• pigmentation