Effects of Ration Limitation and Low Temperature on Growth, Biochemical Condition, and Survival of Juvenile Summer Flounder from Two Atlantic Coast Nurseries

Abstract

Laboratory experiments were conducted on juvenile summer flounder Paralichthys dentatus (25–80 mm total length) from Delaware and North Carolina nurseries to compare their responses to temperature and to ration limitation. Ad libitum feeding rates, maximum growth rates, and growth efficiency were measured at temperatures from 2 to 20°C. Although ad libitum feeding rates did not differ between fish from the two locations, North Carolina juveniles had higher maximum growth rates and growth efficiencies than Delaware juveniles between 6 and 18°C. Growth rates and changes in biochemical condition were also measured for different rations at temperatures that persist during the months following settlement (10–16°C). Survival was high (>98%) after 10–14 d of starvation and suboptimal rations at 10–16°C, but growth rates were highly dependent on feeding rates. Maintenance rations remained constant between 10 and 16°C, but scope for growth increased with temperature, Scope for growth of North Carolina juveniles was higher than that of Delaware juveniles between 10 and 16°C, and growth rates of North Carolina juveniles were more sensitive to changes in ration. Changes in RNA:DNA ratios over the course of each 10–14-d experiment depended primarily on ration; ratios increased as temperature and feeding rate increased. Low-temperature tolerance (at 1–4°C) of juveniles was highly dependent on the rate of temperature decline, not on feeding rate, Time until 50% mortality (LT50) varied from 14 d (–1.3°C/d, fast rate) to 31 d (–0.3°C/d, slow rate); North Carolina juveniles were significantly less tolerant of decreasing temperatures than were Delaware juveniles.