<p><i>Crassostrea ariakensis</i> (Jinjiang oyster) is characterized by rapid growth, strong stress resistance, and large body size. It mainly occurs in estuarine areas with salinities ranging from 10 to 25, with salinity notably affecting its growth, development, and reproduction. Therefore, this study evaluated the effects of varying salinity levels (15, 18, 21, 24, 27, and 30) on these characteristics and on immune responses in <i>C. ariakensis</i>. The survival rate of adult oysters was considerably lower at salinity 30 than that of the other groups (<i>P</i>&lt;0.05). Gonadal development was in the most advanced stage in the 18 group, whereas it was significantly delayed in the 30 group. Compared to other salinity levels, oocyte diameter was the largest and significantly smaller in these two groups (<i>P</i>&lt;0.05). Similarly, larvae reared at salinity 18 or 30 exhibited the highest and lowest growth and survival rates, respectively (<i>P</i>&lt;0.05). Immune indices of larvae revealed the lowest activities of superoxide dismutase, catalase, alkaline phosphatase, and levels of malondialdehyde at salinity 18. However, the activities of the three enzymes were elevated at salinity 21. Malondialdehyde content was markedly higher in the salinity 30 group than in the others (<i>P</i>&lt;0.05). These findings suggest that salinity 18 is the optimal for gonadal development in adult <i>C. ariakensis</i> as well as for larval growth and survival, unlike 27 and 30, which are unsuitable.</p>