Ration, Growth, and Measures of Somatic and Organ Condition in Relation to Meal Frequency in Winter Flounder, Pseudopleuronectes americanus, with Hypotheses Regarding Population Homeostasis

Abstract

Six ration levels were established among 120 large, adult winter flounder (Pseudopleuronectes americanus) by setting different feeding frequencies, but with unlimited feeding at each meal. All fish were maintained at 7 C. With decrease in feeding frequency, fish ate less food per month but more food per meal — i.e. ration compensation was attempted. At the lowest frequency, two meals per month, fish did not compensate. At any one feeding frequency, fish ate progressively more per meal from the first to the fourth (final) month of the experiment.Maintenance ration was 7.9 gcal/g per day. Weight loss on starvation was equivalent to 2.14–2.35 gcal/g per day. Gross conversion efficiency ranged from 1 to 16%, and was positively correlated with ration. Net conversion efficiency averages 24.3% and was not related to ration.Positive correlations were found between mean calories consumed per day and condition, liver weight, percent fat in the liver, percent of fish with yolk-bearing ovaries, ovary weight, and percent of ovarian follicles with yolk. The decrease in proportion of yolked oocytes with decrease in ration was not due to increased follicular atresia, but to a decrease in number of oocytes starting vitellogenesis.Comparisons with flounders sampled directly from Passamaquoddy Bay, N.B. showed that the negative correlation between condition index and percentage of oocytes not in vitellogenesis was the same for Bay and laboratory fish, the range of response being greater in the laboratory fish. The existence of this relationship was interpreted as evidence that some flounders within the Bay were not getting all the food they could use. In the face of food scarcity, the winter flounder’s adaptive reproductive strategy seems to be to sacrifice egg production and maintain body weight, and so when a good year comes its body will be large and able to carry a larger ovary.