The objectives of this trial were to determine the apparent digestibility coefficients (ADC) of crude protein and amino acids for two species of free floating aquatic macrophytes (Eichhornia crassipes and Pistia stratiotes) by Nile tilapia (Oreochromis niloticus) and to determine the water quality of digestibility aquariums in relation nitrogen and phosphorus concentrations. Tree feeds were developments, containing 0.10% of chromic oxide - III, one being the reference diet (purified) and the others containing 30% of aquatic macrophytes. The Nile tilapias (58.8 + 18.5 g) were fed to apparent satiation and the faeces were collected by modified Guelph system. The average ADC of crude protein and amino acids were, respectively, 93.17 and 93.32% for diet reference; 59.23 and 60.35% for E. crassipes; and 52.24 and 57.40% for P. stratiotes. No significant differences were observed among the ADC of protein and of amino acids of the plants ingredients. The results showed lower efficiency by tilapia of Nile in assimilate the most amino acids of the E. crassipes and P. stratiotes. It is possible to conclude that excretory products in the Nile tilapia increase the concentrations of nitrogen and phosphorus, independent of feed.
amino acids; artificial eutrophication; Eichhornia crassipes; feedstuffs; nutrients; Pistia stratiotes
