Evaluation of digestibility coefficients of some carbohydrate-rich feedstuffs for Indian major carp fingerlings

An evaluation of the apparent dry matter, crude protein, fat, carbohydrate and energy digestibility coefficients in nine raw and two stream-cooked agro-based by-product pelleted feeds (ratio of reference:test ingredient = 70:30) containing 30-32% crude protein, 3.9-4.3 kcal g-1 energy and 1% chromic oxide was carried out in three species of Indian major carp fingerlings, Catla catla (Hamilton) (length =4-6 cm: weight = 1.5-2.5 g), Labeo rohita (Hamilton) (length = 3.9-6.2 cm; weight = 1.5-2.7 g) and Cirrhinus mrigala (Hamilton) (length = 4.1-6.0 cm: weight = 1.6-2.8 g). Each dietary treatment had three replicates of 25 fish each. The experimental trial was conducted in 70-L high-density polyvinyl flow-through (1-1.5 L min-1) indoor circular troughs (water volume = 55 L). Fish were fed to apparent satiation, twice daily at 0800 and 1600 h. Faecal samples were collected by siphoning daily at 0700 and 1500 h. The results indicated that apparent dry matter, nutrient (protein, fat and carbohydrate) and energy digestibility coefficients varied significantly within each test species (P < 0.05) for the feedstuffs tested. However, with few exceptions, digestibility for an individual ingredient varied insignificantly (P > 0.05) among the three fish species. The present study clearly indicated that feedstuffs rich in carbohydrate and energy are effectively utilized by the fish. The variations observed in dry matter, nutrient and energy digestibility coefficients in these species seemed related to the type and nutrient composition of the feedstuffs. Feedstuffs and test diets with higher levels of fibre and ash showed significantly (P < 0.05) low values for dry matter, nutrient and energy digestibility. Steam-cooking of yellow corn and potato significantly (P < 0.05) improved the digestibility coefficients. The findings of the present study are important for the development of low-cost balanced rations which incorporate locally available agro-based by-products for the polyculture of the three species of Indian major carp.