| Summary: | The Portuguese oyster <i>Crassostrea angulata</i> shows great potential in oyster farming. In Europe, pure populations of this species were observed only in the southern coasts of Portugal and Spain, namely in Rio Sado, Rio Mira and Guadalquivir. The conservation of <i>C. angulata</i> populations is important in the context of production diversification and biodiversity preservation. In this way the zootechnological development for seed hatchery production is extremely important. Broodstock conditioning is a key step in the process of rearing bivalve in hatchery. Many factors regulate the reproductive cycle, being food the most important. However the influence of the nutritional quality of different phytoplankton on sexual maturation has been poorly explored. To evaluate the effects of different diets on <i>C. angulata</i> sexual maturity, broodstock were conditioned with different food regimes: Diet 1: bi-specific combination of <i>Pavlova lutheri</i> and <i>Isochrysis galbana</i> clone T-ISO (1:1); Diet 2: tri-specific combination of <i>P. lutheri</i>, <i>I galbana</i> clone T-ISO and <i>Skeletonema constatum</i> (1:1:1); Diet 3: bi-specific combination of <i>S. constatum</i> and <i>Chaetoceros calcitrans</i> (1:1) and Diet 4: tri-specific combination of <i>P. lutheri, S. constatum</i> and <i>C. calcitrans</i> (1:1:1). During conditioning, condition index and gonad histological analysis were performed. Results showed heterogeneity between diets. At the beginning of conditioning 60% of individuals were in resting (stage 0), 30% were males in early gametogenesis (stage I) and 10% were females in mature stage (stage III). At the end of the conditioning, the most effective diet was the Diet 3 (60 % of mature oysters with a mean condition index value of 2.83±0.95). Whereas those fed with Diet 1 have an unsuccessfully gonadic development, with 80% of individuals in resting stage. Indeed, the condition index, in Diet 1 decreased during the conditioning period. The results obtained in this study reinforce the idea that the diatom microalgae group is essential in the conditioning of <i>C. angulata</i> broodstock. This work constitute an important first step in the hatchery <i>C. angulata</i> broodstock nutrition and a prerequisite for future work on improvement of broodstock conditioning and the optimization of feeding practices that will maximize the conditioning phase and minimize cost in aquaculture hatcheries.
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