“…Digestive enzymes found in the fish alimentary system directly affect digestion and absorption of nutrients, animal growth, and adaptability to the environment (Xia et al, 2017). The growth and digestibility responses to different dietary protein levels have been reported for several species, such as redclaw crayfish Cherax quadricarinatus (Figueiredo, Kricker, & Anderson, 2001), sea cucumber Apostichopus japonicus (Xia et al, 2017;Bai, et al, 2016), meagre Argyrosomus regius (Saavedra, et al, 2018), and pacific white shrimp Penaeus vannamei (Huang, Wang, & Lu, 2003). Although Kim et al (2016) evaluated the individual and combined effects of oxygen concentration and diet composition on growth and nutrient utilization of O. niloticus (Ling, Hashim, Kolkovski, Chong, & Chien, 2006), the effects of dietary protein levels on muscle quality and digestive enzyme activities of GIFT-O.…”