Realized Heritability and Genetic Gain of Growth Traits in the Portuguese Oyster, <i>Crassostrea angulata</i>

Selective breeding is a fundamental tool for improving growth performance in aquaculture species. This study evaluated the realized response to selection, heritability, and genetic gain for three economically important traits consisting of shell length, soft tissue weight, and whole weight in the commercial edible Portuguese oyster ( Crassostrea angulata ) across three consecutive selection generations (S4, S5, and S6) and their respective control lines (C4, C5, and C6). A family‐based breeding design was implemented, and growth traits were measured at five time points during the grow‐out period (120, 180, 210, 270, and 365 days). The results revealed consistent genetic improvement in all three traits, with whole weight exhibiting the highest realized heritabilities (0.35–0.90) and genetic gains (up to 11.13%). Shell length and soft tissue weight also showed moderate realized heritabilities (0.11–0.79), with substantial genetic gains achieved over successive generations (7.69%–19.22%). Comparisons between the selected and control lines confirmed the effectiveness of the selection protocol. At 120 days, the whole weight of the S4 and S5 lines exceeded their respective controls by 8.7% and 11.1%. Moreover, at subsequent time points (180, 210, 270, and 365 days), genetic gains in the selected lines were significantly greater than in the control lines, with all improvements surpassing 8.5%. These findings demonstrate the efficacy of family‐based selection in C. angulata and highlight the potential for further genetic improvement of the lines under selection.