Quantification of endogenous marker acid-insoluble ash in commercial aquaculture ingredients and feeds

This study investigates the efficacy of acid-insoluble ash (AIA) as an endogenous digestibility marker in commercial aquaculture ingredients and feeds. AIA is a naturally occurring, low-cost alternative to external markers such as chromic oxide and yttrium oxide. External markers are often impractical in the production of small batches of feed manufactured under commercial settings due to cost and logistical constraints. This manuscript is the first of its kind to quantify the AIA content of 18 commercial aquaculture feeds and 27 commercial ingredients from diverse origins, as well as the recuperation rate of pure AIA. Samples were acquired from various national and international sources based on currently available stock; all samples were analyzed in quadruplets for statistical analysis. Results indicated significant variation in AIA levels across different ingredient categories (p < 0.05), with marine-based meals and rendered animal meals exhibiting the highest AIA concentrations (up to 25.8% and 5.0%, respectively), while vegetable meals displayed the lowest AIA content (up to 0.2%). Shrimp and crab meals had particularly high AIA levels due to their mineral-rich exoskeletons (4.7% and 25.8%, respectively), and meals that had undergone certain commercial processing to increase the meal quality had lower AIA content than their regular counterparts (avian: 2.9% for high quality and 4.4% for regular quality; meat: 0.13% for high quality and 0.8% for regular quality). Additionally, a limit of quantification (LOQ) was determined to define the confidence range of the utilized AIA protocol. This study highlights the importance of considering diet composition and ingredient origin in diet formulation to ensure consistent nutritional outcomes. Furthermore, we demonstrate that a wide range of commercial diets contain a quantifiable amount of AIA. The findings suggest that AIA can serve as a reliable and cost-effective marker for in-vivo digestibility studies, aiding feed manufacturers and farm managers in optimizing production performance by rapidly assessing feed quality.