Abstract
Experiments were conducted to determine the effects of excess dietary cobalt (Co) on bioaccumulation, digestive enzyme activities, and growth in freshwater Cyprinus carpio. Four isonitrogenous diets (average crude protein: 35%) were formulated to prepare a control diet (T
1
) with no Co, and three Co-supplemented diets with 1 (T
2
), 1.5 (T
3
), or 2 (T
4
)% Co. The results showed that C. carpio fed with T
3
diet showed maximal apparent protein digestibility, feed conversion, protein utilization, and growth. Protease and lipase activities were maximal in the fish group given T
3
diet. Accumulation of Co in different soft and hard tissues of fish did not correlate with levels of Co in the diet. The concentration of Co in the water increased with dietary level, being at a disturbing adverse effect level at 2% dietary Co. Evidence indicates that an additional supply of dietary Co up to a level of 1.5% is a viable option to augment growth of C. carpio, but at higher levels of Co it may be detrimental to fish health and the aquatic ecosystem.