DESCRIPTION OF THE STARVING CONDITION IN SUMMER FLOUNDER, PARALICHTHYS DENTATUS, EARLY-LIFE HISTORY STAGES

The nutritional status of laboratory-reared summer flounder, Paralichthys dentatus, larvae and early juveniles was assessed by morphometric, biochemical, and histological criteria. Conditions of food deprivation were imposed on 6-, 16-, and 33-day-old larvae as well as on 60-day-old juveniles. Samples of ad-libitum-fed or starved individuals were analyzed with regard to standard length, dry weight, eye diameter to head height ratio, pectoral angle, RNA:DNA ratio, total protein content, histological appearance of selected organs, and cell height of the anterior and posterior intestinal mucosae. In general, tolerance to starvation increased with age: 60 h in 6-day-old-larvae, 72 h in 16-day-old larvae, 8 d in 33-day-old-larvae, and 10 d in 60-day-old-juveniles. The results of this study demonstrate that morphological criteria are either not good indicators of nutritional status (eye:head ratio), good only for larvae (pectoral angle), or require extensive calibration (standard length and dry weight). They also show that biochemical criteria are either not good indicators (protein content) or are sensitive to starvation only in juveniles (RNA:DNA ratio). Among the histological criteria, thickness of the posterior intestinal mucosa was the most sensitive and consistent indicator of starvation in summer flounder larvae and early juveniles. The most salient attributes of this histological analysis were sensitivity, objectivity, ease of interpretation, and exemption from shrinkage calibration. These results suggest the use of the histological approach in the face of uncertainties associated with the other methods examined. On the other hand, application of either morphological or histological criteria is appropriate for an aquaculture setting in which age of larvae is known.