The effects of dissolved oxygen and dietary protein levels on growth performance, physiological parameters and the immune response of the genetically improved farmed tilapia juveniles (Oreochromis niloticus).

A 6‐week feeding trial was conducted to investigate the effects of dissolved oxygen (DO) levels on growth performance, physiological parameters and the immune response of juvenile GIFT fed with three different levels of dietary protein. Triplicate groups of fish (0.45 ± 0.01 g) were fed 30%, 40% and 50% protein diet at hypoxia (2.0 ± 0.3 mg/L) and normoxia (6 ± 0.4 mg/L). The fish were hand‐fed to apparent satiation twice a day (8:00 am and 16:00 pm). Fish growth, feed intake and feed conversion ratio were adversely affected by hypoxia. However, fish growth improved with the increasing dietary protein levels. Feed intake endured the individual and combined effects of DO and dietary protein levels. Somatic indices reduced significantly after hypoxia exposure, with the interaction effects observed on the viscerosomatic index. Red blood cells reduced with decreasing DO levels. Apart from glucose, the serum biochemical modules increased at hypoxia. Triglyceride was affected by the interaction of the factors of interest. Alanine aminotransferase, glucose and total protein contents were significantly changed by the experimental diets, wherein the excess and lower protein levels triggered the increased values of these parameters. Hypoxia diminished liver oxidation enzymes and serum complement component 3. Lipase and amylase were negatively affected by low DO. Experimental diets influenced the cytochrome C oxidase and lactate dehydrogenase in the muscle and gill; besides, cytochrome C oxidase in the gill was also altered by DO, whereas that in the muscle was affected by the interaction of DO and diets. These data show that hypoxia is detrimental to growth performance, feed utilization, liver and immunity. [ABSTRACT FROM AUTHOR]