The Effects of Latitudinal Origin and Paternal Contribution on Larval Growth of Winter Flounder in a Northern Environment

Abstract

Three stocks of winter flounder Pseudopleuronectes americanus are currently defined in the northwest Atlantic region: One south of Cape Cod, Massachusetts, one north of it, and a third on Georges Bank. Our objectives were to determine whether the different populations along this latitudinal gradient have similar larval development characteristics in a coldwater environment and to test the paternal contribution to larval development. We crossed breeders that had been captured on their natural spawning sites in Passamaquoddy Bay, New Brunswick, and Baie des Chaleurs and the St. Lawrence estuary, Quebec, to produce pure-strain families (year 1) and hybrids (year 2). Larvae were reared under the salinity and temperature conditions of the St. Lawrence estuary, the northernmost site in our study. Total length and maximum width were measured from hatching to settlement. In the wild population from the St. Lawrence estuary, males were shorter and in better condition and females produced smaller eggs than those from the two more southern wild populations. The time lapse between fertilization and hatch was shorter for embryos from the Baie des Chaleurs. In both the pure and hybrid cross experiments, the different cross-types showed similar fertilization and hatching success, size at hatch and settlement, and time until settlement but differed in larval growth rate. Larval growth was slower in families sired by St. Lawrence estuary males. When females from the Baie des Chaleurs were crossed with males from the different origins, the results were similar to those obtained in families sired by St. Lawrence estuary males. These results strongly suggest a paternal component to larval growth. Settlement, however, which appeared to be size dependent, was governed more by environmental factors than by parental ones.