Gonadic conditioning of the calafia mother-of-pearl oyster, Pinctada mazatlanica (Hanley, 1856), under two temperature regimes

Gonadic conditioning of pearl oyster Pinctada mazatlanica was studied under two water temperature regimes using cultured specimens. Before starting co nditioning, specimens were induced to spawn with thermal shock. Two differe nt regimes were evaluated, controlled temperatures (CT) and gradually incre asing temperatures (IT). In both trials, specimens were fed daily with Isoc hrysis galbana and Chaetoceros gracilis in a proportion of 7:3. Gonad and m uscle samples were excised from the oysters every 15 days and processed for histological analysis. Condition Index and Muscle Condition Index were cal culated. Similarly, oocyte frequency and oocyte diameter measurements were made. ANOVA analyses were used to test significant differences in the frequ ency and diameter of postvitellogenic oocytes, and values of both condition indexes between temperature regimes, and over time. The IT showed more sui table conditions for gonad conditioning than CT, although the time needed f or reaching maturity was higher in the former regime. For CT, a temperature of 24 degreesC was the best for conditioning, since there were no traces o f atretic oocytes, partially spawned specimens, and there were less previte llogenic oocytes and more postvitellogenic oocytes filling the follicles. A t 20 degreesC, no positive results were noticed. Condition indexes appear t o be reliable indicators of gonad activity during conditioning in both tria ls. The ANOVA analysis detected significant differences in almost all the s tatistical treatments run for oocyte frequency, oocyte diameter and conditi on indexes according to temperature regime and over time. (C) 2001 Elsevier Science B.V. All rights reserved.