Protein is the most important component of any fish feed for its role in growth, especially during the larval stages, and its high cost. Fish meal continues to be a major source of protein in fish feed production. But its supply cannot keep pace with everexpanding aquaculture production, leading to its high cost. Plants are being considered as potential replacements in the search for new alternatives to fish meals. But their application depends significantly on their digestibility in target species. The present study aims to determine the protein content of four locally available plants Moringa oleifera, Ipomoea aquatica, Lemna minor and Salvinia natans, and test their digestibility in vitro by using the pH drop method in two important food fish Anabas testudineus and Channa punctata, of Assam, India. The crude protein in all plants ranged from 19-29%, and the highest crude protein was observed in Lemna minor (29.9 ± 2.34%). The in vitro digestibility was estimated by calculating the RPD% (relative protein digestibility) using casein as a standard reference. Digestibility of the plant proteins exhibited species-specific variations. The RPD% ranged from 50.39% to 75.39% in A. testudineus, and 41.38% to 54.02% in C. punctata compared to that of casein (100%). The highest RPD% was observed in I. aquatica (75.39%) for A. testudineus, and the lowest (50.39%) in L. minor whereas, in C. punctata, the highest RPD% was observed in L. minor (54.02%) and the lowest in I. aquatica (41.38%). The digestibility of all plant proteins was comparatively higher in A. testudineus than in C. punctata. Our results indicate that I. aquatica and L. minor may be a suitable replacement for animal protein in the diet of A. testudineus and C. punctata, respectively, because of their good protein content and high digestibility. Moringa may be considered for utilization in the fish feed as it recorded good protein and digestibility. This information may be useful in developing a cost-effective, plant-based protein diet for the two fish species for their mass production. Keywords: Anabas testudineus, Channa punctata, In vitro digestibility, Ipomoea aquatica, Plant proteins

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Knowledge of the feeding habit and the digestive physiology of a fish is important in making appropriate strategies for feed development and successful culture. Nutrient-rich small indigenous fish species (SIFs) are abundant in Assam, India. Puntius sophore, Mystus tengara, and Trichogaster fasciata of Gossaigaon, Assam are important SIFs for the local rural population, and also potential candidates for ornamental fish culture. The present study aims to evaluate the feeding habit and digestive enzyme activities of these species. Data obtained from the relative gut length and gut content analysis suggested that M. tengara is a carnivorous fish and the rest two fishes are omnivorous in habit. Further, the relative gut length was highest in T.  fasciata (4.20±0.45) and lowest in M. tengara (0.55±0.11). Digestive enzyme activity indicates a correlation with the dietary habit of the fish. Further, total protease, trypsin, and amylase activity was reported highest in P. sophore. Acid protease pepsin was found to be significantly higher in M. tengara complementing its carnivorous habit and gut anatomy. The present study has established some important information on the digestive enzyme characteristics and feeding habits of the three fish species. This information might be useful in the development of suitable feed for the fish species for their culture.