Dietary Supplementation of Organic Zn Improves Digestive Enzyme Activities, Antioxidant Response, and Growth Performance of Nile Tilapia Oreochromis sp

This research aimed to evaluate the effects of dietary organic zinc (Zn) supplementation at different levels on various physiological parameters in Nile tilapia (Oreochromis sp.). Triplicate groups of nile tilapia (8.3 ± 0.02 g) were fed diets supplemented with different levels of organic Zn (0, 20, 40, 80 and 160 mg kg-1) for 60 days. The study focused on assessing digestive enzyme activities (lipase, amylase, chymotrypsin, and trypsin), intestinal morphometry (villus width, villus height, and absorption surface area), antioxidant response (superoxide dismutase and malondialdehyde), health status (lysozyme activity and respiratory burst), growth performance, and organ zinc content. The results revealed significant outcomes. Digestive enzyme activities increased up to 40 mg kg-1 of dietary Zn, but declined at higher levels. Fish fed Zn-supplemented diets at 20-80 mg kg-1 exhibited enhanced absorption surface area, while the control group (0 mg kg-1) and the highest dose (160 mg kg-1) showed reduced absorption surface area. After an air exposure challenge, the antioxidant response showed significantly higher superoxide dismutase (SOD) activity at Zn levels of 20 and 40 mg kg-1, with the lowest malondialdehyde (MDA) levels observed at 40 mg kg-1. Furthermore, fish fed diets with 40 mg kg-1 Zn demonstrated significantly higher lysozyme activity, while respiratory burst was elevated in tilapia receiving Zn doses of 20 and 40 mg kg-1. Growth performance parameters improved significantly up to 40 mg kg-1 of dietary Zn, beyond which they declined. The Zn requirement was estimated to be 38.4 mg kg-1 based on the specific growth rate using broken-line regression analysis. Tilapia fed diets containing Zn levels ranging from 20 to 80 mg kg-1 showed notable improvements in protein retention, final biomass, and feed intake. The survival rate remained unaffected by the experimental diets. Zinc content in the liver, muscle, and intestine did not exhibit significant changes with varying dietary Zn levels. These findings provide valuable insights into the effects of dietary organic Zn supplementation on Nile tilapia, contributing to the development of optimized nutritional strategies for enhancing growth performance and overall health in aquaculture production systems.