<![CDATA[Salinity is a key environmental factor affecting physiological performance and immune responses in shrimp aquaculture, particularly during adaptation to low-salinity culture systems. However, information on how reduced salinity influences both cellular and humoral immune responses in juvenile Litopenaeus vannamei remains limited, making it necessary to evaluate immune-related responses under different salinity conditions. This study evaluated the effects of different salinity levels on survival, hemocyte profiles, and selected cellular and humoral immune responses of juvenile L. vannamei. Shrimp (2.50 ± 0.28 g) obtained from a commercial hatchery were reared at salinities of 3.5, 7, 14, and 28 g L⁻¹ in triplicate for 14 days. Measured parameters included survival rate, total hemocyte count (THC), differential hemocyte count (DHC), phagocytic activity, phenoloxidase activity, and lysozyme activity. Salinity significantly affected survival and most immune-related parameters. Survival increased progressively with increasing salinity, reaching 86.67 ± 3.85% at 28 g L⁻¹ and declining to 48.89 ± 5.88% at 3.5 g L⁻¹. THC was highest at 14 g L⁻¹ (2.61 ± 0.12 × 10⁴ cells mm⁻³) and decreased markedly under reduced salinity conditions. Similarly, phagocytic and phenoloxidase activities were significantly reduced at lower salinities, whereas lysozyme activity was not significantly affected. Overall, suboptimal salinity conditions below 7 g L⁻¹ imposed physiological stress on L. vannamei juveniles, leading to impaired immune responses and reduced survival.Salinitas merupakan faktor lingkungan penting yang memengaruhi performa fisiologis dan respons imun dalam budidaya udang, khususnya selama adaptasi pada sistem budidaya bersalinitas rendah. Namun, informasi mengenai bagaimana penurunan salinitas memengaruhi respons imun seluler dan humoral pada juvenil Litopenaeus vannamei masih terbatas, sehingga diperlukan evaluasi terhadap respons imun pada kondisi salinitas yang berbeda. Penelitian ini mengevaluasi pengaruh berbagai tingkat salinitas terhadap kelangsungan hidup, profil hemosit, serta respons imun seluler dan humoral terpilih pada juvenil L. vannamei. Udang dengan bobot 2,50 ± 0,28 g yang diperoleh dari hatchery komersial dipelihara pada salinitas 3,5; 7; 14; dan 28 g L⁻¹ dengan tiga ulangan selama 14 hari. Parameter yang diamati meliputi tingkat kelangsungan hidup, total hemocyte count (THC), differential hemocyte count (DHC), aktivitas fagositik, aktivitas fenoloksidase, dan aktivitas lisozim. Salinitas berpengaruh nyata terhadap kelangsungan hidup dan sebagian besar parameter imun. Kelangsungan hidup meningkat seiring meningkatnya salinitas, dengan nilai tertinggi pada 28 g L⁻¹ sebesar 86,67 ± 3,85% dan terendah pada 3,5 g L⁻¹ sebesar 48,89 ± 5,88%. Nilai THC tertinggi diperoleh pada salinitas 14 g L⁻¹ sebesar 2,61 ± 0,12 × 10⁴ sel mm⁻³ dan menurun pada salinitas rendah. Aktivitas fagositik dan fenoloksidase juga mengalami penurunan nyata pada salinitas rendah, sedangkan aktivitas lisozim tidak menunjukkan perbedaan nyata. Secara keseluruhan, kondisi salinitas suboptimal di bawah 7 g L⁻¹ menyebabkan stres fisiologis, menekan respons imun, dan menurunkan kelangsungan hidup udang uji.]]>
