Abstract
This research evaluated the influence of yeast and zinc on growth performance and metabolic responses of Nile tilapia. Diets were formulated to contain 32.0% digestible protein and 3,240 kcal DE/kg diet and the following autolized yeast (%):zinc (mg/kg)relationships: 0.0:0.0; 0.0:79.5; 2.0:0.0; 0.795:79.5; 2.0:200; 4.0:400; 6.0:600; 12.0:1,200 and 14.0:1,400. It was used 135 fingerlings (7.27 ± 0.19 g), distributed in a complete random design in 27 50-L aquaria and they were fed ad libitum four times a day for 128 days. It was evaluated growth performance and metabolic responses, weight gain, apparent feed conversion; protein efficiency and survival rate; percentage of protein, ether extract, dry weight and ashes in the muscle and in the bones; ammonia concentration and kinetic activity of alkaline phosphatase in the liver; ammonia, kinetic activity of alkaline phosphatase, urea and lipids in the plasma and; minerals in plasma, in the liver and in the bones of the fish. High levels of yeast and zinc in the diet impaired growth performance and metabolic responses of the fish. Autolized yeast at the level of 2.0% determines the best growth performance. Levels higher than 6.0% of autolized yeast and 600 mg zinc in the diets impair growth performance and lipid metabolism in fish and levels higher than 4.0% of autolized yeast and 400 mg zinc/kg in the diet impair mineral metabolism.
Highlights
Diets which meet nutritional requirements and provide better health conditions are an important tool to prevent disease outbreaks and to improve production efficiency
This research evaluated the influence of yeast and zinc on growth performance and metabolic responses of Nile tilapia
This study aimed at evaluating growth performance and metabolic response of Nile tilapia fingerlings fed diets supplemented with autolised yeast and zinc
Summary
Diets which meet nutritional requirements and provide better health conditions are an important tool to prevent disease outbreaks and to improve production efficiency. Yeast was used as protein source in fish diets in the last decade, its high nitrogen-free extract content (Butolo, 2002) and its deficiency in sulphur amino acids (Furuya et al, 2000) have made its inclusion unfeasible in fish diets. It showed promising results in growth improvement (Li & Gatlin III, 2003), health (Hisano et al, 2007ab) and immune response in fish (Li & Gatlin III, 2004) as a functional food. These additional properties enable yeast to be included in animal diets in lower levels
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