Digestibility and postprandial ammonia excretion in Nile tilapia (Oreochromis niloticus) fed diets containing different oilseed by-products Kwasi Adu Obirikorang • Stephen Amisah • Simon Cudjoe Fialor • Peter Vilhelm Skov Received: 26 July 2014 / Accepted: 12 January 2015 Ó Springer International Publishing Switzerland 2015 Abstract The present study was undertaken to evaluate the potential for using oilseed by- products (soybean, copra and palm kernel meals) as partial replacements of fishmeal in feeds for Nile tilapia (Oreochromis niloticus). Nutrient digestibility and postprandial ammonia excretion rates were examined. A fishmeal-based diet served as control against three test diets in which 30 % of each of the oilseed by-products was included. Diets were randomly assigned to triplicate groups of fish (*1 kg bulk weight) for the digestibility trials which spanned a total of 9 days. The partial inclusion of oilseed meals did not significantly affect apparent protein digestibility, although lipid, ash and dry matter digestibilities were significantly affected (p \ 0.05). Fish fed the soybean meal diets significantly reduced their feed intake and showed lower growth and feed utilization efficiencies over the trial period. The inclusions of the plant proteins caused a reduction in ammonia excretion rates with the palm kernel meal diet recording the lowest mean excretion rates of 117 mg kg -1 day -1 which was twofold lower than the highest mean daily ammonia excretion rate of the fish group fed the fishmeal-based control diets. Overall, the study confirmed the potential of using copra and palm kernel meals to partially replace fishmeal in Nile tilapia diets based on their effects on short-term growth and feed utilization, nutrient digestibilities and lower ammonia excretion rates, while soybean meal in an unrefined form is not a promising replacement for fishmeal in tilapia diets. Keywords Ammonia excretion  Digestibility  Growth  Oilseed meals  Postprandial  Tilapia K. A. Obirikorang (&)  S. Amisah  S. C. Fialor College of Agriculture and Renewable Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana e-mail: quasiadu@gmail.com P. V. Skov DTU Aqua, Section for Aquaculture, The North Sea Research Centre, Technical University of Denmark, PO Box 101, 9850 Hirtshals, Denmark 123 Aquacult Int DOI 10.1007/s10499-015-9881-z