The efficiency of high-altitude trout farming: Which is more critical, dissolved oxygen or temperature?

Key Findings

• The study demonstrates that as altitude increases, the economic efficiency of trout farms decreases.

• The negative impact of low dissolved oxygen (DO) levels at high altitudes outweighs the benefits of colder, trout-favorable water temperatures.

• Improving oxygen levels with technology (PSA systems) leads to a much more significant increase in efficiency than relying solely on eggs with a better feed conversion ratio (FCR).

The rainbow trout (Oncorhynchus mykiss) is one of the most cultivated fish species worldwide and in Iran, valued for its rapid growth and market value. Two environmental factors are crucial for its optimal development: temperature and dissolved oxygen (DO). Fish farms located at high altitudes would seem to have a natural advantage, benefiting from the colder water temperatures ideal for the species.

However, these locations present an inherent challenge: as altitude increases, atmospheric pressure decreases, reducing oxygen solubility in the water. This creates a paradox: does the benefit of ideal temperatures offset the detriment of lower oxygen levels? Most importantly, what is the net impact on the economic efficiency (EE) of these farms?

A recent study by scientists from Texas A&M University, Tarbiat Modares University, the Norwegian Institute of Bioeconomy Research (NIBIO), and the University of Kentucky addressed this question for the first time. Conducted in Mazandaran province, a major trout-farming region in Iran, the results could change investment and management strategies for producers in similar high-altitude conditions.

How was efficiency measured on the Iranian farms?

To unravel this complex relationship, researchers collected direct data from 25 trout farms (15 propagation and 12 grow-out) in Mazandaran during 2018. The methodology involved two key steps:

1. Data Envelopment Analysis (DEA): This powerful non-parametric tool was used to calculate the economic efficiency of each farm. The DEA model compares the inputs used (such as imported and domestic eggs, feed, labor, and energy) with the outputs generated (marketable trout and domestic eggs). This identifies the most efficient farms and measures how much others can improve.
2. Tobit Model: Once the efficiency scores were obtained, an econometric Tobit model was applied to determine how the “altitude” variable influenced these scores.

This approach not only measured efficiency but also identified a key environmental factor that determines it.

Altitude reduces economic efficiency

The study’s results shed light on the challenges faced by high-altitude trout farmers and pointed to a clear culprit.

A surprisingly low average efficiency

The first revealing finding was that the average economic efficiency of all studied farms was merely 0.43 (or 43%). This indicates there is 57% room for improvement in resource use to reach the optimal performance seen in the most efficient farms within the group.

Propagation farms (which produce their own eggs) showed slightly higher efficiency (47%) than grow-out farms (38%). This low overall efficiency is particularly noteworthy because many of these farms benefit from government subsidies for importing foreign eggs, which have a better feed conversion ratio (FCR).

Dissolved oxygen: The limiting factor

The Tobit model analysis was conclusive: it found a statistically significant and negative relationship between altitude and economic efficiency. In simple terms, as the altitude of the fish farms increased, their profitability decreased.

This evidence confirms the study’s central hypothesis: the negative impact of reduced dissolved oxygen levels at higher altitudes surpasses the positive effect of colder water temperatures. A DO level below 6 mg/L can cause hypoxia, stress, a weakened immune system, a worse FCR, and higher mortality, directly affecting production and costs.

Evaluating solutions: Beyond genetics

With the main problem identified, the study explored which strategy would be most effective for improving the EE of these farms.

PSA technology as a game-changer

Since low DO is the primary bottleneck, researchers proposed a technological solution: the use of Pressure Swing Adsorption (PSA) oxygen generators. These systems take ambient air and concentrate the oxygen to inject it into the water, ensuring optimal levels for fish growth, even at high altitudes.

The analysis showed that installing a PSA system that runs for just two hours a day can dramatically increase DO levels, the “vital index” of the fish, and consequently, the production of marketable trout.

Simulating the future: Two paths to profitability

To quantify the benefit, two scenarios were evaluated, assuming the subsidy for imported eggs was reallocated to purchasing PSA equipment for 17 farms with suboptimal DO:

• Scenario 1 (Technology + Improved Genetics): Farms install PSA systems and replace imported eggs with genetically improved domestic eggs (with an FCR similar to imported ones).
  • Result: Average economic efficiency increased to 50%.
• Scenario 2 (Technology + Standard Genetics): Farms install PSA systems but use standard domestic eggs, with no genetic improvement in FCR.
  • Result: Average economic efficiency increased to 49%.

The most important finding from this simulation is that the great leap in efficiency (from 43% to 49%) comes from improving dissolved oxygen via PSA technology. Genetic improvement in FCR contributes only an additional 1% to efficiency.

Conclusion and recommendations for the sector

This study, while specific to the Mazandaran region, offers a fundamental lesson for high-altitude aquaculture in other parts of the world, like Peru and Bolivia: environmental management is the priority. The results conclusively show that in high-altitude conditions, efforts and investments must first focus on solving environmental limitations, such as low dissolved oxygen, before addressing other factors like genetics.

The recommendation for aquaculture policymakers is clear: reallocating subsidies from imported eggs to the acquisition of oxygenation technology like PSA systems is a more effective strategy with a greater impact on boosting the sustainability and profitability of mountain trout farming. For trout producers, this study underscores the importance of actively monitoring and managing oxygen levels, viewing it as a critical investment for the economic success of their operation.

Contact
Seyed Habibollah Mosavi, Department of Agricultural Economics, Tarbiat Modares University
Tehran, Iran.
Email: shamosavi@modares.ac.ir

Reference (open access):
Asadikia, H., Mosavi, S. H., Ashrafi, T. A., Reed, M. R., Hegde, S., Alamdarlo, H. N., & Khalilian, S. (2025). Exploring the economic efficiency of trout farms: The dual impact of temperature and dissolved oxygen at high altitudes. Journal of the World Aquaculture Society, 56, e70047. https://doi.org/10.1111/jwas.70047

Milthon Lujan

Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.