Gametogenic cycle and reproductive effort of the tropical blacklip pearl oyster, Pinctada margaritifera (Bivalvia : Pteriidae), cultivated in Takapoto atoll (French Polynesia)

The gametogenic cycle and the reproductive effort of the blacklip pearl oys ter, Pinctada margaritifera, cultivated in Takapoto lagoon were studied for a 1-year period (March 1997-April 1998) by bimonthly observations of gonad al sections, dry tissue weights and gonadal index in a population of pearl oyster composed of three age-groups. pearl oysters attained sexual maturity in the end of their first year (height approximate to 40 mm), implying tha t P. margaritifera is a late-maturing species in comparison with other Pter iidae. This species was also confirmed to be a marked protandrous successiv e hermaphrodite in culture, with 100 % of males at first maturity and 75 % in older pearl oyster (height > 120 mm). The general pattern of gametogenic activity, fairly synchronous in both sexes, was comparable with that of ot her tropical bivalves: reproduction occurs continuously throughout the year with a maximal activity during the warm season (November-May). No resting period was observed. Quantitative growth data showed that P. margaritifera exhibits an annual synchronised polymodal spawning pattern, with two spawni ng peaks in age-group I (height approximate to 70 mm) and five in age-group s II (height approximate to 100 mm) and III (height approximate to 120 mm). Spawning was sometimes incomplete, nevertheless a clear relationship betwe en gamete production (P-R, g) and size (height H, mm) was obtained: P-R = 5 .26 x 10(-7) H-2.91 (R-2 = 0.99, p < 0.05). Estimation of P-R was used to c alculate the annual reproductive effort in P. margaritifera. Reproductive e ffort (%) was similar to those calculated for temperate species and showed a progressive increase with the age of pearl oyster, from 7 % in age-group I to 38 % in age-group III. This study showed that, in a fairly stable trop ical environment such as the Takapoto lagoon, P. margaritifera is a multipl e spawner, which uses an opportunistic reproductive strategy, allowing inve stment all year around, of any surplus energy into gamete production. Surpl us energy is ensured by the high pumping rates developed by this non-symbio tic bivalve to succeed in low seston conditions. (C) 2000 Ifremer/Cnrs/Inra /Ird/Cemagref/Editions scientifiques et medicales Elsevier SAS.