ISSUE FOCUS 80 FEED & ADDITIVE MAGAZINE August 2025 Even after digestion and absorption, nutrients particularly proteins are not fully accessible to fish without additional metabolic processing. To use amino acids for energy, fish must first undergo deamination, an energy-consuming process that removes the amino group. This contributes to SDA, which is externally observed as an increase in oxygen consumption shortly after feeding, followed by elevated ammonia excretion (Brett & Groves, 1979). The proportion of amino acids deaminated varies depending on environmental and nutritional conditions. Fish maintained at low temperatures or on restricted rations often deaminate most or all amino acids, using them primarily for energy. In contrast, fish experiencing rapid growth and consuming high-protein diets deaminate a smaller proportion of amino acids, although the absolute amount may still be significant enough to result in a high SDA. The energy required for deamination can be supplied by carbohydrates or fats, which can reduce the need to metabolize protein for energy. This "protein-sparing" effect, particularly from carbohydrates, has been widely applied in salmonid aquaculture to lower feed costs while maintaining growth. However, the role of lipids in protein sparing has received less attention. Although SDA can be reduced through dietary strategies, it cannot be entirely eliminated due to the inherent costs of nutrient processing. MEASUREMENT AND CALCULATION To measure and calculate SDA in aquaculture, following are the steps: 1. Experimental Setup: Design an experiment where you can monitor the metabolic rate of the fish before and after feeding. 2. Baseline Measurement: Measure the baseline metabolic rate of the organisms. This can be done using respirometry techniques, where you measure oxygen consumption or carbon dioxide production over a period of time. 3. Feeding: Feed the organisms with a known quantity and type of food. It's essential to ensure that the food is similar to their natural diet to minimize confounding variables. 4. Post-Feeding Measurement: Again after feeding measure the metabolic rate of the organisms. To capture the peak metabolic response to feeding this should be done for a sufficient period of time. 5. Data Analysis: Calculate the difference between the post-feeding metabolic rate and the baseline metabolic rate. This difference represents the increase in metabolic rate due to the specific dynamic action of feeding. 6. Statistical Analysis: Perform statistical analysis to determine if the observed increase in metabolic rate is significant and to compare SDA among different treatments or species. 7. Repeat and Validate: Repeat the experiment multiple times to ensure reproducibility and validate the results. It's important to note that the specific protocols and techniques for measuring SDA may vary depending on the species of and the specific research objectives. Additionally, consider factors such as temperature, salinity, and other environmental conditions that may influence metabolic rate and SDA. OPTIMIZING SDA FOR IMPROVED EFFICIENCY SDA plays a critical role in influencing feed conversion ratios (FCR) within aquaculture. It affects feed requirements, nutrient utilization efficiency, and the metabolic responses of species to feeding. Species exhibiting higher SDA tend to require an increased amount of feed to satisfy their energy needs, which leads to greater feed consumption for equivalent output and consequently raises the FCR. Therefore, the implementation of effective management techniques and feed optimization strategies is essential to mitigate the impact of SDA on FCR while fostering sustainable aquaculture practices. Feed Formulation: To improve efficiency, choose feeds that induce lower SDA responses. High-quality, easily digestible feeds with balanced nutrient profiles can reduce the energy expended during di-
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