Immunostimulating effect of triiodothyronine: dietary administration of triiodothyronine in rohu (Labeo rohita) enhances immunity and resistance to Aeromonas hydrophila infection

The immunomodulatory effects of dietary administration of 3,3^′,5‐triiodo‐l ‐thyronine (T₃) at 0, 1, 5 and 10 mg  kg^?1 of diet for 60 days in rohu (Labeo rohita) fingerlings were studied. Oral administration of T₃ at all dose levels resulted in significantly (P<0.05) higher serum T₃ levels, total serum protein and globulin levels, and reduced albumin–globulin ratio (A : G) compared with the control group, whereas feeding of T₃ at 5 and 10 mg kg^?1 diet enhanced the growth and superoxide production by neutrophils. At the end of the 60‐day experimental period the optimum dosage of T₃ appeared to be the 5 mg  kg^?1 diet for rohu fingerlings, resulting in a significantly higher specific antibody titre against formalin‐killed Aeromonas hydrophila and lowering the mortality percentage against the A. hydrophila challenge.