The amount of food provided in each diet was registered on a daily basis. The uneaten diet in each tank was removed every day before feeding with a suction tube and stored in separate recipients into the refrigerator, depending of the experimental unit. After seven days, the removed uneaten diet was defrosted and dried in a 55°C oven for 24 h. The removed uneaten diet was discounted from the food placed into each tank and then, the actual food consumption for each tank was determined.