A study of the osidasic profile in the digestive tract of some herbivorous fish species living in tropical freshwaters of French Guiana has been undertaken. Osidase APY-ZYM plates allowing the study of the last stages of the polyosides lysis were used. The results show that Arius parkeri and Arius couma have low scores but without any staring enzymatic particularities; Myleus ternetzi gives similar results. Compared with the species. Leporinus granti and Hoplosternum thoracatum have more diversified and increasing scores; Hypostomus watwata exhibits a number of striking top performances and general superiority over other species. These preliminary results are discussed according to the possible fish aptitude to digest complex glucids of the diet.