Concentration-dependent recovery of gills and hepatopancreas in juvenile Penaeus vannamei during long-term exposure to high alkalinity

This work aimed to evaluate tissue restoration in the gills and hepatopancreas of juvenile Penaeus vannamei during long-term exposure to high alkalinity. A 30-day experiment was conducted using four experimental groups with three replicates each: T120 (control), T200, T300, and T400, corresponding to alkalinity levels of 120, 200, 300, and 400 mg CaCO₃/L, respectively, adjusted with sodium bicarbonate (NaHCO₃). Juveniles ( n = 336; 1.5 ± 0.8 g) were stocked at 28 shrimp/m 2 in 60 L tanks with filtered seawater. Tanks were continuously aerated, and water temperature was maintained at 27 ± 1 °C. Shrimp were fed a commercial diet (35% crude protein) four times daily. Histological samples were collected on Days 0, 14, and 30. Shrimp at 200 and 300 mg CaCO₃/L exhibited reversible morphological changes in both organs, whereas those at 400 mg CaCO₃/L showed pronounced tissue damage, with only partial hepatopancreas recovery after 30 days. These results indicate that P. vannamei exhibits a concentration-dependent capacity for tissue recovery under sustained high alkalinity, maintaining structural integrity up to approximately 300 mg CaCO₃/L.