Welfare and Performance

A Study Stablishes the Optimal Density that Ensures Trout Welfare and Productive Performance

China, 13 November 2025 | For the first time is defined biochemical welfare thresholds that producers can monitor

Truchas arcoíris en estanques

The optimal stocking density for rainbow trout (Oncorhynchus mykiss) farm is estimated to be between 28.36 and 36.63 kilograms per cubic metre, according to a study recently published in the scientific journal Aquaculture.

The research not only confirms that high densities are detrimental, but also establishes an optimal biomass range and, for the first time, defines biochemical welfare thresholds that producers can monitor.

As noted in the study, operating within this range ensures that the fish maintain a high Specific Growth Rate (SGR) while avoiding an increase in the Feed Conversion Ratio (FCR), which rises sharply at higher densities. This results in lower feed costs per kilogram of fish produced.

The study also demonstrated that chronic stress induced by overcrowding affects glucose metabolism, pushing the fish into a catabolic (degrading) rather than anabolic (growing) state. To help fish farmers assess welfare without having to wait for visible growth reduction, the research proposes biochemical safety thresholds.

A fasting serum cortisol level above 83.42 nanograms per milliliter indicates chronic stress and growth suppression. Similarly, a serum glucose level above 3.56 millimoles per litre reflects excessive energy mobilization to cope with stress – at the expense of energy needed for growth and other biological functions.

As the authors point out, investment in rigorous control of stocking density is not only an ethical matter but also a fundamental economic strategy. Excessive density triggers a stress response that not only halts growth but also reduces the fish’s ability to utilise feed efficiently.

By adhering to these biochemical parameters, the researchers conclude, that producers can ensure a healthier product and a more profitable business.