Antinutritional factors present in plant-derived alternate fish feed ingredients and their effects in fish

The use of plant-derived materials such as legume seeds, different types of oilseed cake, leaf meals, leaf protein concentrates, and root tuber meals as fish feed ingredients is limited by the presence of a wide variety of antinutritional substances. Important among these are protease inhibitors, phytates, glucosinolates, saponins tannins, lectins, oligosaccharides and non-starch polysaccharides, phytoestrogens, alkaloids, antigenic compounds, gossypols, cyanogens, mimosine, cyclopropenoid fatty acids, canavanine, antivitamins, and phorbol esters. The effects of these substances on finfish are reviewed. Evidently, little unanimity exists between the results of different studies as to the specific effects of antinutrients, since most studies have been conducted using an ingredient rich in one particular factor and the observed effects have been attributed to this factor without considering other antinutrients present in the ingredient, or interactions between them. Tentatively, protease inhibitors, phytates, antigenic compounds, and alkaloids, at levels usually present in fish diets containing commercially available plant-derived protein sources, are unlikely to affect fish growth performance. In contrast, glucosinolates, saponins, tannins, soluble non-starch polysaccharides, gossypol, and phorbol esters, are more important from a practical point of view. The effectiveness of common processing techniques such as dry and wet heating, solvent extraction and enzyme treatment in removing the deleterious effects of antinutrients from feed materials is discussed. More insights into the nutritional, physiological and ecological effects of antinutrients on fish need to be accumulated through studies using purified individual antinutrients and their mixtures in proportions similar to those in alternative nutritional sources in fish feeds. Such studies would provide data useful for designing optimum inclusion levels of plant-derived materials and treatment methods that would neutralise the negative effects of the antinutritional factors. (C) 2001 Elsevier Science B.V. All rights reserved.