Stable Differences in Growth Rates of Juvenile Triploid Oysters <i>Crassostrea gigas</i>

Abstract

The three groups of mollusks of the triploid Pacific oyster Crassostrea gigas from the Liman Donuzlav (Black Sea), differing in morphometric characteristics: fast growing (FG) – shell height (H) 40 mm, medium growing (MG) – 15 mm H 40 mm and slow growing (SG) – H 15 mm, were studied. The stable differences in the growth rates of juveniles of the same age were revealed. Mollusks of the FG group were the leaders in terms of weight gain and linear size throughout the study. The average daily increase in shell height in the studied mollusks ranged from 0.1 to 0.35 mm/day, with maximum values in June and September. Weight gain occurred with different intensity, on average in SG – 0.051 g/day, in MG – 0.168 g/day, in FG – 0.287 g/day. The peaks of this indicator were in August and September, reaching 0.12, 0.26 and 0.43 g/day, respectively. A negative allometry of the shell in height was obtained in slow–growing polyploid oysters (b = 2.17), in the other two other groups – a clear positive (for MG b = 3.23, for FG b = 3.80), i.e., the increase in mass was faster than linear growth in juveniles of the species. Polyploidy (triploidy) is suggested as the reason for the differences in the growth rates of the same-aged mollusks. The allometry indicator b can be used to identify growth features in the early stages of oyster development.