According to Gram Research analysis, salmon fed the highest vitamin A levels (100,000 IU/kg) developed significantly paler color and retained only 4.8% of dietary astaxanthin—a natural pink pigment—compared to fish on lower vitamin A diets. A 2026 aquaculture study found that excessive vitamin A interferes with how salmon’s cells process and store astaxanthin, reducing flesh color from 27.1-27.5 on the SalmoFan scale to just 3 mg/kg concentration. When stressed through crowding and low oxygen, salmon lost additional color unless they received both high vitamin A and high astaxanthin together.
Researchers studied how vitamin A affects astaxanthin—a natural pink pigment—in farmed salmon. They found that when salmon ate diets with very high vitamin A levels, the fish couldn’t use the pink pigment as well, resulting in paler flesh. The study also showed that stress (like crowding) made salmon lose their color even more, unless they had high vitamin A in their diet. This research helps fish farmers understand how to feed salmon to keep them healthy and maintain their natural pink color that consumers expect.
Key Statistics
A 2026 aquaculture research article found that Atlantic salmon fed the highest vitamin A concentration (100,000 IU/kg) retained only 4.8% of dietary astaxanthin in their flesh, compared to higher retention rates at lower vitamin A levels, resulting in significantly paler color development.
According to a 17-week salmon feeding trial published in 2026, salmon exposed to stress conditions (crowding and low oxygen) lost approximately 0.5 mg/kg of astaxanthin from their muscle tissue, except those fed high vitamin A combined with high astaxanthin, which maintained 3.3 mg/kg.
A 2026 cellular study of Atlantic salmon found that liver cells from fish fed high dietary vitamin A converted 39% of astaxanthin into other compounds, compared to only 6% conversion in liver cells from salmon fed low vitamin A diets.
Research published in 2026 showed that salmon fed the highest vitamin A levels had astaxanthin flesh concentrations of just 3 mg/kg, the lowest among all dietary groups tested, with digestibility rates as low as 12% at the highest astaxanthin feeding level.
The Quick Take
- What they studied: How different amounts of vitamin A in salmon feed affect the fish’s ability to use astaxanthin (a natural pink pigment) and maintain their color, especially when stressed.
- Who participated: Young Atlantic salmon living in seawater, fed six different diet combinations over 17 weeks, then some were exposed to stress conditions for 5 additional weeks.
- Key finding: Salmon fed the highest vitamin A levels (100,000 IU/kg) had the lowest pink color and used astaxanthin poorly. When stressed, salmon lost color unless they had high vitamin A combined with high astaxanthin in their diet.
- What it means for you: Fish farmers can optimize salmon feed to maintain better color and health by balancing vitamin A and astaxanthin levels. This research is primarily relevant to aquaculture producers rather than consumers, though it affects the quality of farmed salmon available in markets.
The Research Details
Researchers divided young Atlantic salmon into six groups, each receiving different combinations of astaxanthin (the pink pigment) and vitamin A in their feed for 17 weeks. They measured how much pink color the salmon developed, how much astaxanthin ended up in the fish’s flesh, and how well the fish’s bodies processed the pigment. After 17 weeks, four of the groups were exposed to stressful conditions—crowding and low oxygen—for 5 more weeks to see how stress affected the pigment.
To understand what was happening inside the fish’s bodies, scientists isolated cells from the liver and intestines and studied how these cells processed astaxanthin in laboratory conditions. They used radioactive labeling to track exactly what happened to the pigment as the cells broke it down and converted it into other compounds.
The researchers also measured changes in gene expression—essentially looking at which genes turned on or off in response to different diets and stress conditions. This helped them understand the biological mechanisms behind their observations.
This research approach is important because it combines real-world feeding trials with laboratory cell studies and genetic analysis. By studying both what happens in the whole fish and what happens at the cellular level, the researchers could explain not just that vitamin A affects astaxanthin use, but also how and why it happens. This multi-level approach makes the findings more reliable and useful for fish farmers.
The study was published in a peer-reviewed journal focused on aquaculture nutrition, indicating it met scientific standards. The researchers used controlled laboratory conditions and measured multiple outcomes (color, pigment concentration, cell metabolism, and gene expression), which strengthens confidence in the results. However, the study was conducted in a single facility with one fish species, so results may not apply to all salmon farms or other fish species. The sample size was moderate, which is typical for aquaculture research but means some findings should be interpreted cautiously.
What the Results Show
Salmon fed the highest vitamin A concentration (100,000 IU/kg) developed the palest color and had the lowest astaxanthin in their flesh (3 mg/kg), compared to fish on lower vitamin A diets. The fish also retained less of the pink pigment—only 4.8% to 8.9% of the astaxanthin they ate stayed in their bodies, and their digestive systems absorbed even less (12% to 29% depending on the diet).
When researchers studied liver and intestinal cells in the laboratory, they discovered that high dietary vitamin A caused the cells to convert astaxanthin into other compounds instead of keeping it intact. Liver cells from salmon fed high vitamin A converted 39% of the astaxanthin into other forms, while liver cells from salmon fed low vitamin A only converted 6% of it.
Stress significantly affected the salmon’s ability to maintain their pink color. Fish exposed to crowding and low oxygen lost about 0.5 mg/kg of astaxanthin from their muscle tissue. However, salmon that had been fed both high vitamin A and high astaxanthin maintained their color better during stress, keeping 3.3 mg/kg of astaxanthin in their flesh.
Gene expression analysis showed minor changes in immune, stress, and metabolic genes in response to different diets and stress conditions. This suggests that vitamin A and astaxanthin affect not just pigmentation but also how the fish’s body responds to challenges. The interaction between diet and stress was complex—vitamin A and astaxanthin didn’t simply add up their effects, but instead worked together in ways that depended on the specific combination.
This research builds on earlier studies showing that vitamin A can interfere with carotenoid (pigment) absorption in fish and other animals. The finding that high vitamin A reduces astaxanthin retention confirms previous observations but provides new detail about exactly where and how this interference happens—at the cellular level during metabolism. The stress component adds new information, as most previous studies didn’t examine how environmental stress interacts with nutritional factors.
The study was conducted with only one species of salmon in one facility, so results may not apply to all salmon farms or other fish species. The researchers didn’t measure all possible outcomes—for example, they didn’t assess whether the color differences affected consumer preferences or fish market value. The stress period (5 weeks) was relatively short, so long-term effects of stress on pigmentation remain unclear. Additionally, the study focused on young salmon in seawater; results might differ for salmon at different life stages or in freshwater environments.
The Bottom Line
Fish farmers should avoid feeding salmon excessively high vitamin A levels if maintaining pink color is important, as very high vitamin A (100,000 IU/kg) significantly reduces astaxanthin utilization. A moderate vitamin A level (6,500-35,000 IU/kg) combined with adequate astaxanthin (60 ppm) appears to support both good color development and stress resilience. These recommendations are based on controlled research but should be adapted to individual farm conditions and market requirements. Confidence level: Moderate to High for the vitamin A effect; Moderate for stress interactions.
Fish farmers and aquaculture feed manufacturers are the primary audience for this research. They can use these findings to optimize feed formulations for better salmon color and health. Consumers who buy farmed salmon may indirectly benefit through improved product quality. This research is less relevant to people eating wild salmon or those not involved in fish farming.
Changes in salmon flesh color develop gradually over weeks. Based on this 17-week study, farmers should expect to see noticeable color improvements within 8-12 weeks of adjusting feed vitamin A levels. The effects of stress on color can appear within days to weeks of exposure to crowding or poor water conditions.
Frequently Asked Questions
Does too much vitamin A prevent salmon from turning pink?
Yes. A 2026 study found that salmon fed the highest vitamin A levels (100,000 IU/kg) developed significantly paler color and retained only 4.8% of dietary astaxanthin, the pink pigment. High vitamin A interferes with how salmon’s cells process and store astaxanthin.
How does stress affect salmon color in farmed fish?
Stress from crowding and low oxygen causes salmon to lose approximately 0.5 mg/kg of astaxanthin from their muscle tissue. However, salmon fed high vitamin A combined with high astaxanthin maintained better color (3.3 mg/kg) during stress conditions.
What vitamin A level is best for salmon feed to maintain color?
Research suggests moderate vitamin A levels (6,500-35,000 IU/kg) combined with adequate astaxanthin (60 ppm) support good color development. Avoid the highest vitamin A levels (100,000 IU/kg), which significantly reduce astaxanthin utilization and flesh color.
Can salmon recover their pink color after stress?
The 2026 study measured color loss during a 5-week stress period but didn’t track recovery afterward. Salmon with adequate dietary astaxanthin and moderate vitamin A maintained better color during stress, suggesting proper nutrition helps resilience.
Why does vitamin A interfere with astaxanthin in salmon?
Laboratory cell studies showed that high dietary vitamin A causes salmon liver and intestinal cells to convert astaxanthin into other compounds instead of keeping it intact. This metabolic conversion reduces the amount of pink pigment available for storage in muscle tissue.
Want to Apply This Research?
- For aquaculture users: Track weekly salmon flesh color using the SalmoFan color scale (target 27.1-27.5) alongside feed vitamin A concentration (in IU/kg) and astaxanthin levels (in ppm). Record any stress events (crowding, oxygen drops) and correlate with color changes.
- Aquaculture managers can use the app to log daily feed composition, water quality parameters (especially oxygen levels), and stocking density. The app could alert users when vitamin A levels exceed recommended ranges or when stress indicators appear, prompting feed adjustments before color loss occurs.
- Establish a baseline color measurement at the start of a feeding cycle, then measure weekly using standardized methods. Track the ratio of vitamin A to astaxanthin in feed, and monitor stress indicators (crowding density, oxygen levels). Use the app to identify patterns between feed adjustments and color outcomes over multiple production cycles.
This research applies specifically to Atlantic salmon farming and aquaculture feed formulation. The findings are not directly applicable to human nutrition or wild salmon. Fish farmers should consult with aquaculture nutritionists before making significant changes to feed formulations, as individual farm conditions, water quality, and market requirements vary. This research describes one study’s findings and should not be considered the sole basis for commercial feed decisions. Always follow local regulations and best practices for aquaculture management.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.