Simultaneous effect of stocking density, dietary aflatoxin B1 and medicinal plant multi-blend on digestive physiology of rainbow trout (Oncorhynchus mykiss)

The effect of stocking density and dietary aflatoxin B1 along with including rosemary and thyme powders on digestive enzymes activity of rainbow trout was evaluated. 600 fish with an average weight of 90±3 were randomly allotted into six experimental groups consisted of (1) stocking at 15 kg.m^-3- feeding diet devoid of aflatoxin, (2) stocking at 45 kg.m^-3-feeding diet devoid of aflatoxin, (3) stocking at 15 kg.m^-3-feeding diet containing 50 ppb aflatoxin, (4) stocking at 45 kg.m^-3-feeding diet containing 50 ppb aflatoxin, (5) stocking at 15 kg.m^-3-feeding diet containing 4% rosemary and thyme powder and 50 ppb aflatoxin and (6) stocking at 45 kg.m^-3-feeding diet containing 4% rosemary and thyme powder and 50 ppb aflatoxin. Activity of alkaline protease, lipase and amylase was only affected by fish stocking density to the extent that those fish were reared in higher density showed increased digestive enzymes activity (p<0.05). Interactive effect of two studied factors (stocking density and dietary supplementation of medicinal plants) significantly affected activity of amylase and alkaline protease. However, lipase was only affected by dietary supplementation of medicinal plants. The highest amylase and alkaline protease activity were recorded in those fish received diet devoid on medicinal plants and stocked at 45 kg.m^-3 (p<0.05). Those fish received diet containing medicinal plant powder significantly had lower activity (p<0.05). Proximal intestine histological examinations revealed that those fish stocked at higher density and received aflatoxin contaminated diet had villi detachments. Nevertheless, dietary inclusion of herbal blend consisted of rosemary and thyme powder could retrieve such tissue abnormality. It seemed that intestine could resist tension from higher stocking density or dietary aflatoxin contamination; however, their combination was not endurable for fish. Meanwhile, further complementary researches such as assaying antioxidant enzymes activity are warranted to precisely elucidate the underlying mechanism behind such alterations.