Effects of dietary tannic acid and quebracho tannin on growth performance and metabolic rates of common carp ( Cyprinus carpio L.)

Abstract

The effects of tannic acid (a hydrolysable tannin) and quebracho tannin (a condensed tannin) on common carp at a level of 2% in a soybean and fish meal-based diet containing about 40% crude protein have been studied. Quebracho tannin did not affect feed intake, body weight gain, average metabolic growth rate and oxygen consumption during the experimental period (84 days). The carp grew from an initial body weight of about 30 g to a final body weight of 150 g, and the carcass composition was also not affected by quebracho tannin. On the other hand, tannic acid produced adverse effects after day 28. The rejection of diet started on day 28 and a complete rejection of the diet was observed on day 40. The feeding of this diet was discontinued after day 42. The average metabolic growth rate for days 35–42 was significantly lower ( P<0.05) in this group. The oxygen consumption of carp fed a diet containing tannic acid also decreased although non-significantly for this period. It is concluded that the toxicity of tannic acid is higher to carp compared to that of quebracho tannin, and that protein sources of plant origin containing high amounts of tannins and in particular hydrolysable tannins should be used with caution as fish meal substitutes in carp diets.