Scientists studied whether adding essential oils (concentrated plant extracts) to fish food could help preserve the quality of frozen fish fillets. They compared two slaughter methods and tracked how fish meat changed during frozen storage. While the oils didn’t reduce stress during slaughter, they did help keep frozen fish fillets fresher-looking and better-textured for up to 45 days. This research suggests that what fish eat before slaughter might be an important factor in keeping seafood quality high in grocery stores and freezers.

The Quick Take

  • What they studied: Whether adding essential oils (concentrated plant extracts) to rainbow trout feed could help preserve fish fillet quality after slaughter and during frozen storage, and how different slaughter methods affected meat quality.
  • Who participated: Rainbow trout raised in aquaculture farms, divided into groups: some fed regular food and some fed food with 0.02% essential oils added. Fish were slaughtered using two different methods (air asphyxiation and percussion) and their fillets were tracked for 45 days in frozen storage.
  • Key finding: Essential oils in fish feed didn’t reduce stress during slaughter, but fillets from supplemented fish stayed fresher-looking and maintained better texture during 45 days of frozen storage, especially when fish were slaughtered using the more stressful air asphyxiation method.
  • What it means for you: If you buy frozen fish, this research suggests that how the fish was raised and slaughtered affects how long it stays fresh in your freezer. The findings may help fish producers keep frozen seafood higher quality longer, though more research is needed before this becomes standard practice.

The Research Details

Researchers divided rainbow trout into two feeding groups: one with regular food and one with food containing 0.02% essential oils (concentrated plant extracts). They then used two different slaughter methods on the fish—air asphyxiation (suffocation in air) and percussion (a quick blow to the head). They measured stress markers, chemical damage, and meat quality immediately after slaughter and then tracked the frozen fillets for 45 days, measuring how much the meat deteriorated over time.

This approach allowed scientists to test two things at once: whether the diet mattered and whether the slaughter method mattered. They used advanced laboratory techniques to measure specific chemicals in the fish meat that indicate stress and damage, and they assessed the fillets’ appearance, texture, and color using both scientific instruments and visual inspection.

The study was designed to understand what happens to fish meat at the molecular level during and after slaughter, and how different factors (diet and slaughter method) influence this process during long-term frozen storage.

Understanding how to preserve fish quality is important because frozen seafood is a major food source worldwide. If researchers can find ways to keep frozen fish fresher longer, it reduces food waste and helps consumers get better-quality products. Additionally, this research touches on animal welfare—finding humane slaughter methods that also produce better-quality meat benefits both the fish and consumers.

This study used advanced scientific techniques including proteomic analysis (studying proteins in detail) and measurement of specific chemical markers of stress and damage. The researchers measured multiple outcomes rather than just one, which strengthens their conclusions. However, the paper doesn’t specify the exact number of fish studied, which makes it harder to assess statistical power. The study was published in a peer-reviewed journal, meaning other scientists reviewed it before publication. The findings are specific to rainbow trout and may not apply to all fish species.

What the Results Show

Air asphyxiation (suffocation in air) was much more stressful for fish than percussion (a quick blow). Fish slaughtered by air asphyxiation showed rapid breakdown of energy molecules in their muscles, increased chemical damage to fats and proteins, and loss of texture in the fillets—all measured immediately after slaughter.

Essential oils added to the fish feed did not prevent these immediate stress responses. In fact, fish fed the supplemented diet showed slightly increased protein damage at the moment of slaughter. However, this initial disadvantage reversed during frozen storage.

During 45 days of frozen storage, fillets from fish fed essential oils showed slower deterioration. They maintained better color and texture compared to fillets from fish fed regular food. This benefit was especially noticeable in fish that had been slaughtered by the more stressful air asphyxiation method.

The researchers identified specific chemical markers (12-HpEPE, 15-HpEPE, PGD3, and PGE3) that appeared only in asphyxiated fish, suggesting these could be used to detect slaughter-induced stress in the future.

Proteomic analysis (detailed study of proteins) revealed that air asphyxiation caused major changes in glycolytic enzymes—proteins involved in energy production. These changes were much less pronounced in percussion-slaughtered fish. The study also found that the benefits of essential oils became more apparent over time, suggesting these plant extracts work by slowing down chemical damage processes rather than preventing them immediately.

Previous research has shown that essential oils have antioxidant properties (they prevent chemical damage), but most studies tested them in laboratory conditions rather than in living animals. This study is notable because it tested essential oils in actual fish feed and tracked real-world outcomes during frozen storage. The finding that slaughter method significantly affects meat quality aligns with previous animal welfare research showing that stress during slaughter harms product quality. However, the result that essential oils didn’t reduce immediate stress responses contradicts some earlier laboratory studies, suggesting that living organisms may respond differently than isolated cells or tissues.

The study doesn’t specify how many fish were used, making it impossible to assess whether the results are statistically reliable. The research was conducted only on rainbow trout, so results may not apply to other fish species. The essential oil dose (0.02%) was relatively low, and the study didn’t test whether higher doses might be more effective. The study tracked fillets for 45 days of frozen storage, but didn’t examine what happens if fish are thawed and refrozen or stored at different temperatures. Finally, the study didn’t measure consumer preferences or taste, so we don’t know if the texture and color improvements actually matter to people eating the fish.

The Bottom Line

For fish producers: Consider using percussion-based slaughter methods instead of air asphyxiation, as this significantly reduces meat damage. Adding essential oils to fish feed appears to be a safe strategy for extending frozen fillet quality during storage (moderate confidence level). For consumers: This research doesn’t change current recommendations about eating frozen fish, but it suggests that fish quality may improve as producers adopt these practices. No dietary changes are recommended based on this single study.

Fish farmers and aquaculture producers should care most about these findings, as they can directly apply them to improve product quality. Seafood companies and retailers may benefit from understanding how to maintain frozen fish quality longer. Consumers interested in food quality and sustainability should care because this research addresses food waste and product quality. People with specific fish allergies or sensitivities should not change their behavior based on this research. This study doesn’t apply to people who don’t eat fish.

The benefits of essential oils appeared gradually during frozen storage over 45 days. Consumers wouldn’t notice immediate changes, but if producers adopt these practices, frozen fish should maintain quality longer on store shelves and in home freezers. Realistic expectations: improvements in texture and color retention, not dramatic changes in taste or nutritional value.

Want to Apply This Research?

  • If using a nutrition app, track the purchase date and storage duration of frozen fish products. Note the texture and color quality when thawing. Over time, users could compare how long different fish products maintain quality in their freezer, building personal data on which brands or sources stay fresher longest.
  • Users could set reminders to check frozen fish quality at regular intervals (e.g., every 2 weeks) and rate texture and color on a simple scale. This creates awareness of how storage time affects food quality and may encourage using older frozen items before they deteriorate significantly.
  • Create a simple log noting: purchase date, fish type, storage temperature, and quality assessment (color, texture, smell) at 2-week intervals. Over months, users can identify their optimal freezer storage window for different fish types and reduce food waste by using products before quality declines.

This research is specific to rainbow trout and laboratory conditions. The findings have not yet been applied to commercial fish production. Essential oils are not approved as food additives in all countries—regulations vary. This study does not provide medical advice and should not be used to treat any health condition. Consult with a healthcare provider before making dietary changes based on this research. The study was published in January 2026 and represents current scientific understanding, which may evolve as more research is conducted. Individual results may vary based on storage conditions, fish species, and other factors not studied here.