Temperature effects on broodstock conditioning of tropical cupped oyster, Crassostrea (Magallana) saidii

The tropical cupped oyster Crassostrea (Magallana) saidii, formally described in 2021 but historically harvested from the Sungai Muar estuary for over 160 years, faces increasing pressure from stock depletion. Hatchery-based broodstock conditioning is therefore essential to ensure sustainable seed supply, yet the influence of temperature on reproductive physiology in tropical oysters remains poorly understood. This study evaluated the effects of chilled (26.9 ± 0.3 °C), ambient (28.3 ± 0.6 °C), and heated (30.8 ± 0.6 °C) conditioning regimes over 40 days on gonadal development, proximate composition (protein, carbohydrate, lipid, and ash), and fatty acid class profiles. Temperature treatments were associated with differences in the distribution of gonadal stages (0–5), although mean maturity index (MI) did not differ significantly among treatments at individual sampling points (P > 0.05). Proximate composition varied with conditioning regime: protein content was higher in the chilled oysters during the early conditioning phase, whereas lipid content was elevated in heated and ambient oysters during the first 20 days, with convergence among treatments thereafter. Carbohydrate and ash content showed moderate fluctuations but no consistent temperature-related difference (P > 0.05). Fatty acid class analysis indicated that chilled and ambient oysters were generally characterised by higher proportions of unsaturated fatty acids and higher UFA:SFA ratios at most sampling points, whereas heated oysters displayed episodic increases in saturated fatty acids, including elevated SFA proportions at Day-10 and Day-40. Chilled oysters also exhibited relatively low n-6:n-3 ratios at several sampling points, consistent with lipid profiles commonly associated with reproductive conditioning. Overall, modest reduction of conditioning temperature (26.9 °C) was associated with a greater proportion of advanced gonadal stages and comparatively stable biochemical patterns relative to ambient (28.3 °C) and heated (30.8 °C) regimes. These findings provide the first experimental evaluation of temperature-mediated broodstock conditioning in C. saidii and offer practical guidance for temperature management in tropical oyster hatcheries.

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