Abstract:
Acute toxicity and sublethal effects of neem Azadirachta indica seed extract on haematological parameters in Nile tilapia Oreochromis niloticus were studied. Both sexes of young Nile tilapia at the age of 1 month were tested to determine the median lethal concentration (96-hr LC50) for acute toxicity using static bioassay. LC50 value of the extract was 36.25 mg/l. Based on this value, a sublethal concentration for the long-term study was computed at 25.07 mg/l. Blood samplings from both control and treatment groups were done monthly until the seventh month of experimentation. Morphological aberrations in blood cellular elements and changes in blood parameters and blood chemistry including blood glucose, ALP (alkaline phophatase), GOT (glutamic oxaloacetic transaminase) and GPT (glutamic pyruvic transaminase) were observed. From the results, the peripheral blood of Nile tilapia blood cell consisted of erythrocyte, thrombocyte and five types of leukocytes ; lymphocytes, monocytes, neutrophils, basophils and eosinophils. The morphological alterations of erythrocytes were poikilocytosis, extrusion of nuclear material, increased nuclear interchromatin space, vacuolization, appearance of a “ragged” cytoplasmic membrane, hypochromia, gray cytoplasm and division of cell. The hypertrophy of nulcear monocyte and vacuolated neutrophil also appeared. Differential leukocyte counts presented a significant (p ≤ 0.05) elevation in lymphocyte, neutrophil, basophil and eosinophil numbers. By contrast, a significant decrease was exhibited in monocyte number. Correlation between a fall in the total red blood cell, haematocrit and mean cell volume was suggestive of anemia. A significant (p ≤ 0.05) reduction in blood glucose and increase in GPT levels was noted indicating the hypoglycemic and hepatotoxic effects. The morphological changes in blood cell were found earlier than the responce of blood chemistry to the extract in the treatment group. The severity of effect was thus time dependent.
