The method consists of evaluating the in vitro digestibility of phenolic compounds in fish diets, which will employ the species' own enzymatic extracts. Thank you for the information.
Also check https://www.researchgate.net/publication/224890906_Application_of_in_vitro_gastrointestinal_model_to_evaluate_nitrogen_and_phosphorus_bioaccessibility_and_bioavailability_in_fish_fed_ingredients