CoP levels between 0 and 130 g kg 1
. The natural productivity of the pond could explain
why results in pens differed from those in aquaria. In the no feeding treatment, natural
food supported fish growth for 2 weeks and after that period, when the fish reached about
25 g, the available natural food only was enough to maintain fish weight for the remaining
experimental period. Assuming that the same amount of natural food was available to the
fish in the other treatments, the higher FCR values found in pens could result from
overfeeding. Our results have shown that the potential inclusion of CoP in tilapia diets
may be limited up to 130 g kg 1 when fish are raised in earthen ponds and natural food is
available.