REPRODUCTIVE CONDITION OF THE TROPICAL BLACK-LIP PEARL OYSTER, Pinctada margaritifera (LINNAEUS) IN TWO FOOD CONDITIONS

Abstract

Reproductive condition and spawning of black-lip pearl oyster, Pinctada margaritifera was studied in two regimes of food; food-added (AF) and no food-added (NAF) using cultured oysters. Prior to conduct the experiment, 20 oysters of initial sample were collected to observe the gonadal condition. Two different regimes were assessed in the tanks supplied with 10 &micro;m filtered seawater for two months. In AF treatment, oysters were fed daily with algal paste of 200 cells &micro;l-1. Gonad samples were taken from the oysters every month and processed for histological analysis. Condition index (CI) and gonadal maturity were estimated to assess reproductive status, and muscular dry weight (MDW) were calculated to assess an energy storage of oyster in each sampling date. Most of initial oysters were in fully matured. Water temperature and salinity fluctuated from 28.2 to 31.2ºC and from 33.8 to 34.5 ppt, respectively; two parameters were not influenced in oyster reproduction during the study. The CI of oysters in both regimes were constant until a month, but the CI significantly decreased to the lowest level in NAF in two months later (p<0.05). Oyster MDW in AF was not changed in each sampling date while the MDW decreased significantly at two months later in the NAF. Oysters in the AF were spawned in a month later while the ripe gametes of oysters were still remained in the NAF. The AF showed more suitable condition to ready for spawning than the NAF. Interestingly, oysters were not spawned artificially at one month later in the NAF because oysters were maintained their energy level in food lack condition. Our data suggested that the food supply is very important factor to accelerate the spawning activity of P. margartifera in brooding season.