Low levels of Aflatoxin B1 could cause mortalities in juvenile hybrid sturgeon, Acipenser ruthenus ♂ Χ A. baeri ♀

Toxicity of aflatoxin B-1 (AFB(1)) was investigated in juvenile hybrid sturgeon Acipenser ruthenus male x A. baeri female, an important coldwater finfish farmed in China and other countries. Seven experimental diets (Diet A-G) containing different levels of AFB(1) (0, 1, 5, 10, 20, 40 and 80 mu g kg)(-1) diet) were fed to juvenile sturgeon weighing 10.53 +/- 0.17 g kg)(-1) to determine its effect on survival, growth, feed consumption, hematocrit, liver histology as well as muscular and hepatic toxin accumulation. The experiment lasted for 35 days and was conducted in two periods of 25 and 10 days each. No external changes or unusual behaviour was observed in the fish fed diets with AFB(1). Mortality was observed in fish fed with highest levels of AFB(1) (80 mu g kg)(-1) Diet G) from day 12 onwards. After 25 days, fish fed the diet of 80 mu g AFB(1) kg)(-1) showed significant lower survival (50 +/- 5.77%) followed by those fed 40 mu g AFB(1) kg)(-1) diet (80 +/- 5.77%) and 20 mu g AFB(1) kg)(-1) diet (86.66 +/- 3.33%). No significant difference was observed in specific growth rate (SGR) or hepatosomatic index (HSI) between groups. Hematocrit was significantly higher in the fish fed the diet of highest AFB(1). The fish were weighed at day 25 in some treatments (Diets F and G) because of high mortality. However, feeding was continued for another 10 days to observe mortality or behavioural changes if any in the other groups. After 35 days, survival in the fish fed Diet F (40 mu g AFB(1) kg)(-1)) was 40% and those fed Diet E (20 mu g AFB(1) kg)(-1)) was 36.2%. Significant histopathological changes including nuclear hypertrophy, hyperchromasia, extensive biliary hyperplasia, focal hepatocyte necrosis and presence of inflammatory cells were observed in the liver of fish fed high levels of aflatoxin (40 and 80 mu g kg) 1). AFB(1) accumulation in fish muscle and liver increased with increased dietary AFB(1) levels. It could be confirmed that 10 mu g AFB(1) kg)(-1) diet was the maximum allowable level in hybrid sturgeon diet.