Pale fish warning as plant feeds cut key pigment absorption in trout, Chilean study finds.
High plant protein inclusion significantly reduces astaxanthin concentrations in rainbow trout fillets and plasma, according to a new study by researchers at the Universidad de Chile and Universidad de las Américas.
The study, led by Dr. Alejandro Villasante and colleagues, found that fish fed diets with 80% replacement of fishmeal by plant protein showed lower dorsal and abdominal pigmentation scores, reduced lipid digestibility, and impaired absorption of astaxanthin — particularly in its diesterified form.
The mechanism centres on cholesterol and bile acid metabolism. Fish on high plant protein diets showed lower plasma concentrations of both, which directly impairs lipid emulsification and intestinal absorption of fat-soluble compounds like astaxanthin, the study states.
Growth performance also declined. Fish on the high-inclusion diet recorded lower final weight, reduced weight gain, worse feed conversion, and changes in distal gut microbiota compared to the fishmeal control group. Moderate plant protein inclusion did not significantly compromise pigmentation.
The research team plans to run supplementation trials with cholesterol and bile salts to test whether reduced pigmentation can be reversed. They also intend to validate the FXR transporter and bile metabolism pathway mechanistically, characterise antinutritional factors in plant ingredients, and confirm findings across other salmonid species and production contexts.
