EFFECTS OF RATION LIMITATION AND LOW-TEMPERATURE ON GROWTH, BIOCHEMICAL CONDITION, AND SURVIVAL OF JUVENILE SUMMER FLOUNDER FROM 2 ATLANTICCOAST NURSERIES

Laboratory experiments were conducted on juvenile summer flounder Para lichthys dentatus (25-80 mm total length) from Delaware and North Caro lina nurseries to compare their responses to temperature and to ration limitation. Ad libitum feeding rates, maximum growth rates, and growt h efficiency were measured at temperatures from 2 to 20-degrees-C. Alt hough ad libitum feeding rates did not differ between fish from the tw o locations, North Carolina juveniles had higher maximum growth rates and growth efficiencies than Delaware juveniles between 6 and 18-degre es-C. Growth rates and changes in biochemical condition were also meas ured for different rations at temperatures that persist during the mon ths following settlement (10-16-degrees-C). Survival was high (>98%) a fter 10-14 d of starvation and suboptimal rations at 10-16-degrees-C, but growth rates were highly dependent on feeding rates. Maintenance r ations remained constant between 10 and 16-degrees-C, but scope for gr owth increased with temperature. Scope for growth of North Carolina ju veniles was higher than that of Delaware juveniles between 10 and 16-d egrees-C, and growth rates of North Carolina juveniles were more sensi tive to changes in ration. Changes in RNA:DNA ratios over the course o f each 10-14-d experiment depended primarily on ration; ratios increas ed as temperature and feeding rate increased. Low-temperature toleranc e (at 1-4-degrees-C) of juveniles was highly dependent on the rate of temperature decline, not on feeding rate. Time until 50% mortality (LT 50) varied from 14 d (-1.3-degrees-C/d, fast rate) to 31 d (-0.3-degre es-C/d, slow rate); North Carolina juveniles were significantly less t olerant of decreasing temperatures than were Delaware juveniles.