Indian Journal of Experimental Biology Vol. 54, September 2016, pp. 606-611 In vitro digestibility study of some plant protein sources as aquafeed for carps Labeo rohita and Cyprinus carpio using pH-Stat method Jai Gopal Sharma 1 , Ashok Kumar 1 , Deepak Saini 1 , Nawang Lendup Targay 1 , Bronson Kumar Khangembam 2 & Rina Chakrabarti 2 * 1 Department of Biotechnology, Delhi Technological University, New Delhi 110 042, India 2 Aqua Research Lab, Department of Zoology, University of Delhi, Delhi 110 007, India Received 04 June 2014; Revised 13 June 2015 Aquaculture, as a promising food industry, is expected to meet the demand for quality food from the increasing human population. As the diet is critical for feeding farm fish, such a faster growth in the industry is destined to create stress in the fishmeal market to supply diets to the tune. In this context, here, we studied the protein content of 20 plant ingredients, including aquatic weeds, cereals, pulses and oil-cakes using micro-Kjeldahl method and evaluated in vitro digestibility of these ingredients for rohu Labeo rohita and common carp Cyprinus carpio using pH-Stat method. The protein contents of water fern, duckweed, almond oil-cake and soybean product were 20.81, 39.75, 47.78 and 57.48%, respectively. Species- specific digestibility was found for the same plant ingredient. The degree of hydrolysis for water fern, duck weed, almond oil-cake and soybean product were 14.17, 4.80, 17.30 and 3.57%, respectively for rohu and 4.58, 6.03, 12.17 and 3.35%, respectively for common carp. This study showed that incorporation of water fern and almond oil-cake in the diet of rohu, and duck weed and almond oil-cake in the diet of common carp are beneficial considering their protein content and digestibility. These are cost-effective, protein-rich feed ingredients for aquafeed. Keywords: Aquaculture, Aquafeed, In vitro digestibility, Plant protein, Rohu World over, the demand for fish, as an affordable and healthy source of protein, is increasing 1 . Fish consumption by 2030 is estimated at 93.612 million tonnes, with India accounting for 10.74%. Globally, production by aquaculture is 66.6 million tonnes, and Asia accounts for 88.39%, and India 6.3%. By 2030, it is expected to reach 101.2 million tonnes, >60% of fish destined for direct human consumption then. It indicates that aquaculture is the fast growing food-producing sector, and it has potential to meet the increasing demand for quality food. Apparently, such a faster growth would stress the fishmeal market to supply diets to the tune 2 . In India, freshwater aquaculture production contributes about 4.03 million tonnes, 55% of the total fish production, and projected to reach 7.50 million tonnes by 2020 3,4 . Carps account for 85% of freshwater aquaculture production in India 3 . Diets are critical for feeding farmed fish, including breeding. Feed accounts for 40-60% of aquaculture production costs 5 . Protein is the most critical ingredient in fish diets on the basis of cost 6 and growth response 7 . In choosing protein source, fish meal is an option, but expensive and also in high demand. The challenge facing the aquaculture industry is to identify economically viable and environmental friendly alternatives to the fish meal. Thus, the feed industry has given emphasis on the viable utilization of plant sources for formulation of feed. However, plant protein has some limitations due to the presence of antinutritional factors and may require processing to eliminate or reduce such compounds 8 . Moreover, these antinutritional compounds have to be evaluated on the target species to avoid adverse physiological functions in the species, such as inhibiting digestive enzyme activities. To be a viable alternative feedstuff to fish meal in aquafeed, a candidate ingredient must possess certain characteristics, including wide availability, competitive price, easy handling, shipping, storage and use in feed production. Furthermore, it must possess certain nutritional characters, such as low levels of fiber, starch, especially non-soluble carbohydrates and antinutrients, and have a relatively high protein content, favorable amino acid profile, high nutrient digestibility and reasonable palatability 9 . —————— *Correspondence: Phone: +91 11 27666496 E-mail: aquaresearchlab@yahoo.co.in