“…In the present study, weight gain of fish was affected by graded levels of dietary tryptophan, as observed in previous studies in Nile tilapia (Santiago & Lovell, ) and other fish species such as silver catfish, Rhamdia quelen (Pianesso et al., ); African catfish, Clarias gariepinus (Fagbenro & Nwanna, ); hybrid striped bass, Morone chrysops × M. saxatilis (Gaylord, Rawles, & Davis, ); and rohu, Labeo rohita (Abidi & Khan, ). The essential amino acid requirements are generally estimated based on weight gain results (NRC, ), as previously described for many fish species (Ahmed & Khan, ; Gaylord et al., ; Pianesso et al., ; Santiago & Lovell, ). In the present study, the total dietary tryptophan requirement was estimated at 3.4 g/kg, which is lower than the 3.6–3.8 g/kg obtained in Indian major carp, respectively (Ahmed & Khan, ), and higher than 2.1–2.5 g/kg that was estimated for hybrid striped bass (Gaylord et al., ), from 2.4 to 2.7 for stinging catfish (Farhat & Khan, ) and 2.8 g/kg for red drum (Pewitt et al., ).…”