Macroalgae, Macrophytes, Filamentous Algae: ‘Not to Everyone’s Taste’

The increased demand for alternative ingredients in farmed aquatic animal feeds is an urgent need to support the unprecedented growth of aquaculture. Macroalgae and macrophytes have long been undervalued as a food source for fishes and invertebrates. The use of aquatic plants as a substitute for fishmeal has the potential to revolutionize aquaculture in meeting the global demand for protein. In contrast to terrestrial plants, the amino acid profile of certain floating macrophytes appears to meet even the lysine and methionine requirements of common cultured tropical fishes. In addition, this potential feed source also appears to be underutilized, particularly with respect to polyunsaturated fatty acids. The use of marine macroalgae as aquafeed ingredients appears to be less successful to date: Chlorophyceae and Rhodophyceae can be used as whole plants, but Phaeophyceae can only be used as extracts. Pretreatment such as fermentation seems to improve utilization, but this needs further investigation. A few papers that have used fermented aquatic plant diets show that digestibility is often, but not always, increased and subsequent growth performance is not adversely affected, if not improved. In general, antinutrients such as phytic acid or tannins are reduced by fermentation. This issue requires much more empirical work. Nevertheless, a high nutritional potential can be attributed to duckweeds and, to a lesser extent, floating ferns. ‘Omics’ studies, including hologenomics or epigenomics, are rare, as are trials to improve gut microbiota through functional diets to better utilize macroalgae and macrophytes. Interesting studies will follow.