ARTICLE 68 FEED & ADDITIVE MAGAZINE February 2024 pollution and contaminants and toxins level in the environment. It is found that all these are interconnected and vary among different species and their natural habitat. HEAT INCREMENT OF FEEDING & FEEDING LEVEL While considering the post-prandial rate of metabolism, it was found that dietary composition and diets most favourable to growth induce the greatest effect. The magnitude of the post-prandial oxygen intake increases with increasing levels of DE in the diet. Also, the higher the proportion of digestible protein in the diet the greater the relative magnitude of this effect. The most rapidly growing fish show the greatest post-prandial increase in metabolic rate. Under conditions most favourable to growth the increase in metabolic rate following feeding is the greatest. Most workers have found that the magnitude of the post-prandial effect increases in relation to meal size. Many (Hamada & Ida, 1973; Schalles & Wissing, 1976; Caulton, 1978; Vahl & Davenport, 1979; Jobling & Davies, 1980) have found a linear relationship between magnitude and ration size, but exponential increases in apparent SDA with increased energy intake have also been reported (Averett, 1969; Tandler & Beamish, 1979). ENERGY DISTRIBUTION IN RELATION TO FEEDING LEVEL Feeding levels must be high enough to supply maintenance needs and still have energy left in for growth. Efficiency of digestion decreases as feeding level is increased. The trouble is that it becomes a challenge to find a feeding level at which the increased efficiency of energy utilization at a high feeding rate is balanced by the lower efficiency of digestion at the higher feeding rate. As ration size increases, Faecal Energy increases as a proportion of Intake Energy, efficiency of digestion and absorption decreases, growth rate decreases, energy lost in excretory products as a proportion of Intake energy decreases, HjE (Heat of Activity) increases and HwE (Heat of waste formation and excretion) declines. The Basal or standard metabolism in fish is relatively constant under constant environmental conditions. It changes only with temperature, fish size and other confounding factors. The heat of nutrient metabolism is proportional to the level of feeding. The energy excreted in urine and gill excretions is also a function of feeding level. The reduced efficiency at high levels of feeding is shown by the proportionally large area representing faeces at high levels of feeding. The amount remaining for growth Figure 2. Distribution of dietary energy intake in a growing fish at various levels of feeding
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