Diversity of aquatic macrophytes as food and feed components to herbivorous fish - a review

About 50 species of aquatic macrophytes are recorded as food to herbivorous fish either directly or indirectly. These macrophytes represent several families of which major ones are Amaranthaceae, Araceae, Azollaceae, Cabombaceae, Ceratophyllaceae, Characeae, Convolvulaceae, Haloragaceae, Hydrocharitaceae, Lemnaceae, Lentibuliaraceae, Menyanthaceae, Najadaceae, Nymphaeaceae, Polygonaceae, Pontederiaceae, Potamogetonaceae, Salvinaceae, Trapaceae, and Typhaceae. In tropical and sub-tropical countries, there are about 40 numbers of fish species belonging to two major families viz., Cyprinidae and Chichlidae, which directly feed on macrophytes. Importantly, these macrophytes may be used as fish food components and replace costly commercial feed owing to their potential nutrients profile: moisture ranges between 84.1-95.9%, dry matter 4.1-15.9%, crude protein 8.7-26.8%, crude fat 2.2-5.1%, carbohydrate 9.3-35.6%, ash 8.0-25.3%, and crude fibre 15.0-28.1%, with caloric content of 2.47-4.2 kcal g(-1). For this substantial nutrients status, they are blended with feedstuffs and fed to fish. Consequently, herbivores have shown satisfactory growth in respect of food intake, feed conversion ratio and relative growth rate. About 50% of plant protein has been converted to fish protein and even 30% inclusion of macrophytes into prepared feeds has shown better balance of amino acid. With tremendous potentiality as fish food components, utilisation of macrophytes in preparation of fish feed is an opportunity of livelihood to rural people; since aquaculture is one of the fastest growing sectors in agriculture.