Hematological and gill histopathological parameters of three tropical fish species from a polluted lagoon on the west coast of Mauritius

Gill histopathology and hematological primary indices, including blood δ-aminolevulinic acid dehydratase (δALA-D) activity and nucleocytoplasmic ratio of erythrocytes, were assessed in three tropical marine fish species, Scarus ghobban, Epinephelus merra, and Siganus sutor, from the presumably contaminated lagoon of Bain des Dames, Mauritius. Concurrently, the nonpolluted region of Blue Bay/Pt d’Esny was used as a reference site for comparison of fish physiological responses and seawater quality. Bain des Dames showed high seawater mercury content (6.4±0.5 μg/L), traces of iron (70±40 μg/L), and fluctuating biochemical oxygen demand values (0.488±0.171 mg/L day−1). Gill histopathological analysis revealed lesions such as epithelial hyperplasia and inflammation. Similarly, a generalized increase in blood δALA-D activity (131.27–355.76 nmol PBG/ml RBC.h) was recorded. Fish from Bain des Dames showed species-specific hematological responses including normocytic macrocytic blood cells (S. ghobban), macrocytic anemia (S. sutor), and active erythropoiesis (E. merra). Though the species displayed impaired health, attributed to changes in water quality, the blood responses seemingly indicate adaptation to hypoxic conditions arising from both gill degradation and perhaps oxygen-level fluctuations.