Observaciones Biológicas en ostras (Ostrea chilensis Philippi) de Pullinque

The oyster (Ostrea chilensis Phil.) population is analyzed at Pullinque located in the Quetalmahue Gulf (lat. 44° 51' 45'' S. long. 73° 55' 25'' W) forehead of Ancud in Chiloe Island, Chile. It is a natural population repopulated with oysters from the Pullinque oyster fishery collectors. Oysters were collected with a dredge at random. They were obtained monthly for 16 months (January, 1965 to April, 1966), with the following conclusions: 1.- The bank has a surface of 162,698 m². Its population was estimated to have 2,391,661 oysters, with an average density of 14.7 oysters per square meter (Fig. 2). 2.- The population size is uniform ranging from 15 to 18 mm. The smallest oyster having 17 mm and the biggest 87 mm. The highest frequencies (62.4%) are found between 55 and 65 mm. (Fig. 2–3). 3.- Ostrea chilensis is monoecius but it presents alternative sexes. Fecundation is internal and all the egg and larvae development process occurs inside the oyster epibranchial chamber (viviparous oyster) (Fig. 4 a–m). 4.- The liberated larvae is well developed (Fig. 4 g–l) and it has a short planktonic life. 5.- The larvae liberation occurs between September and March (Fig. 6). 6.- The gonads and larvae development is related to the water temperature and the spawning takes place with a temperature between 14 and 22°C. (Fig. 7) 7.- Weight-size relationship. As they increase in size they gain weight (Fig. 10, Annex 5–6). The same thing happens with wet weight and shell weight. The maximum weight of the oyster edible part occurs together with the gonadic ripening in August–September (Fig. 5). Minimum weights were observed between November and February in relation to the larvae liberation. 8.- Oyster growth is shown in Figs. 8–9 and it occurs as follows.