A comparative study was conducted to evaluate the apparent nutrient digestibility of a commercial feed in harvest-size cobia (Rachycentron canadum) weighing 3.18 ± 0.62 kg, using two inert markers: yttrium oxide (Y2O3, YO) and Acid-Insoluble Ash (AIA). Results indicated no significant differences in the Apparent Digestibility Coefficient (ADC) between the two markers across all assessed nutrients, although AIA showed a mean underestimation of 2.32% ± 0.71. Additionally, AIA levels were assessed in 27 commercial ingredients and 18 commercial feeds to determine the presence and quantifiability of AIA. The AIA content in the ingredients ranged from 0.0356% to 25.814%, while in the feeds it ranged from 0.094% to 0.983%. This study demonstrated that endogenous AIA can be used to generate ADC values for harvest-size cobia when fed with a commercially available diet, avoiding the challenge of externally marking.
In-vivo digestibility studies are essential for assessing the quality of commercial ingredients and diets, benefiting both feed manufacturers and fish producers. The aquaculture industry needs a method to determine in-vivo digestibility using available commercial feed, as externally marking a diet is impractical. Acid-Insoluble Ash (AIA), a naturally occurring component of ingredients and feeds, remains after acid treatment and high-temperature ashing. Its ease of use, cost-effectiveness, and natural occurrence make it a valuable in-vivo digestibility marker. Using AIA allows feed manufacturers and aquaculturists to evaluate new diets rapidly and cost-effectively by comparing digestibility values with on-site conventional and reference diets. The objective of this study is to quantify the AIA content in various commercial aquaculture feeds and vegetable, animal, and marine ingredients to determine if they contained sufficient AIA for digestibility studies. Additionally, the study aimed to utilize AIA as an in-vivo digestibility tool for commercial harvest-size cobia. By quantifying AIA in ingredients and commercial diets, the industry can determine if complete diets can be used for in-vivo digestibility trials using the AIA method.