A pot culture experiment followed by field experiments were conducted at Annamalai University Experimental Farm, to optimize the age of fingerlings to be released along with rice herbicides and to study the effect of rice herbicides on fish histopathology. Fingerlings of size 4 - 5 cm, when released 12 days after herbicide application was observed to be safe with 100% survival. Grass carp(Ctenopharyngodan idella) fingerlings were exposed to rice herbicides butachlor 1.5 kg ha-1, oxyfluorfen 0.25 kg ha-1 and thiobencarb 1.5 kg ha-1, 12 days after their application in the respective fields. To observe the impact of herbicides on the histopathology of the fish, the fingerlings were collected from the field trenches treated with herbicides at 15, 30 and 45 days after releasing into the field. The changes observed in the gill tissues are cartilagenous hyperplasia of gill rays, proliferation of lamellar epithelium and vacuolation of cytoplasm of lining epithelium, focal loss of lamellar epithelium and congestion of blood spaces. The changes in muscle tissues are swelling and necrosis of muscle fibres. The changes in liver tissues are congestion of sinosoids, congestion of central vein and proliferation of the bile ductular epithelium.
Key words: Histopathology, grass carp, rice-fish farming, herbicidal impact.
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