Scientists studied Atlantic cod from the Baltic Sea and North Atlantic to understand why some fish populations develop vitamin B1 (thiamine) deficiency. They discovered that as fish grow and prepare to have babies, they move most of their vitamin B1 from muscles and liver into their reproductive organs—sometimes putting 70% of their total vitamin B1 there. This massive shift might explain why some fish populations experience serious health problems during spawning season. The research shows that understanding where vitamins go in a fish’s body is crucial for protecting wild fish populations from dangerous deficiencies.

The Quick Take

  • What they studied: How vitamin B1 (thiamine) moves around inside fish bodies as they grow up and get ready to reproduce, and whether some fish populations have more or less of this important vitamin.
  • Who participated: Atlantic cod of different sizes and ages from two ocean regions: the Baltic Sea (where vitamin B1 deficiency happens regularly) and the North Atlantic (where it rarely occurs).
  • Key finding: Female cod moving about 70% of their total body vitamin B1 into their reproductive organs when preparing to spawn, while vitamin B1 levels in muscles and liver drop as fish mature.
  • What it means for you: This research helps explain why wild fish populations sometimes crash during breeding season. While this doesn’t directly affect humans, it shows how important micronutrients are for animal reproduction and suggests we need to monitor fish health more carefully during spawning periods.

The Research Details

Researchers collected cod of various sizes and life stages from two different ocean regions and measured how much vitamin B1 was present in different body parts: muscle, liver, and reproductive organs. They used specialized lab tests to check the activity of enzymes that depend on vitamin B1 to understand whether the fish were actually deficient or just had lower amounts. By comparing fish from the Baltic Sea (where deficiency problems occur) with fish from the North Atlantic (where problems don’t occur), they could see if geography or life stage made a difference in vitamin B1 levels.

The scientists also looked at different forms of vitamin B1 in different tissues. Vitamin B1 exists in several chemical forms in the body, and the researchers found that different tissues preferred different forms. This detailed approach helped them understand not just how much vitamin B1 was present, but how the body was actually using it.

Understanding where vitamins go in an animal’s body is essential for figuring out why some populations get sick. By studying how vitamin B1 moves around during different life stages, scientists can better predict when fish populations might be at risk and what conditions might trigger deficiency problems. This is especially important because vitamin B1 deficiency can cause mass deaths in fish populations, affecting both wild ecosystems and fishing industries.

This study examined actual fish from natural populations rather than laboratory conditions, which makes the findings more realistic. The researchers used multiple measurement methods to confirm their results, including enzyme activity tests that show whether vitamin B1 is actually being used properly. The comparison between two different geographic regions with different deficiency histories strengthens the conclusions. However, the study doesn’t specify exact sample sizes, which makes it harder to assess statistical reliability.

What the Results Show

The most striking finding was that female cod redistribute vitamin B1 dramatically as they prepare to reproduce. About 70% of a female’s total body vitamin B1 ends up in her reproductive organs at the start of spawning season. This massive shift comes from declining vitamin B1 levels in muscle and liver tissue as the fish mature.

The researchers also discovered that vitamin B1 exists in different chemical forms depending on the tissue. In reproductive organs, a simpler form of vitamin B1 dominated and increased as the organs developed. In contrast, muscle and liver maintained a consistent mix of vitamin B1 forms throughout the fish’s life, with a more complex form being most common.

Interestingly, when the scientists tested liver function using enzyme activity measurements, they found no evidence that the livers were actually deficient in vitamin B1, even in fish from the Baltic Sea where deficiency problems occur. This suggests the fish weren’t experiencing active vitamin B1 deficiency at the time of sampling, but the dramatic redistribution during spawning could create problems at other times.

Vitamin B1 concentrations in muscle and liver generally declined as fish grew larger and matured, which is expected as fish redirect resources toward reproduction. The pattern was consistent across both geographic regions studied, suggesting this is a normal biological process rather than a regional difference. The study also found that fish from the two different ocean regions had similar vitamin B1 status when accounting for their size and reproductive stage, indicating that geography alone doesn’t explain deficiency problems.

Previous research had suggested that Atlantic cod might be particularly sensitive to vitamin B1 deficiency, but this study provides the first detailed look at how vitamin B1 moves through a cod’s body during its life. The findings align with observations that other fish and bird species in the Northern Hemisphere experience thiamine deficiency problems, but this research shows that the problem may be related to the specific demands of reproduction rather than an inability to store the vitamin.

The study doesn’t specify how many fish were sampled, making it difficult to assess whether the findings are statistically robust. The research only measured vitamin B1 at one point in time rather than following individual fish over their entire lives, so it’s unclear exactly when and how quickly the redistribution happens. The study also doesn’t explain why some populations develop deficiency while others don’t, despite similar vitamin B1 redistribution patterns. Additionally, the research was conducted on wild fish, so it’s difficult to control for other factors that might affect vitamin B1 levels, such as diet quality or environmental stress.

The Bottom Line

Based on this research, fisheries managers should monitor fish populations more carefully during spawning season, as this appears to be when vitamin B1 deficiency problems are most likely to occur. The findings suggest that protecting fish health during reproduction is critical for maintaining healthy wild populations. However, this research alone doesn’t provide specific management recommendations—it mainly identifies when and why problems might happen. (Confidence: Moderate—this is observational research that identifies a pattern but doesn’t prove cause and effect.)

Fisheries scientists, environmental managers, and people concerned with wild fish population health should pay attention to this research. Commercial fishing industries that depend on cod stocks should be aware that spawning season may be a vulnerable time for populations. General readers interested in environmental conservation and ecosystem health will find this relevant. This research is not directly applicable to human nutrition, though it highlights the importance of micronutrients in reproduction across species.

This research describes natural biological processes that happen over months to years as fish mature and prepare to spawn. There are no immediate timelines for intervention or change—rather, this research helps explain patterns that occur naturally in fish populations over their lifespans.

Want to Apply This Research?

  • For users interested in fish and wildlife conservation: Track seasonal fish population health reports or spawning season dates for local fish species. Note any mass mortality events or population crashes and correlate them with spawning periods to build awareness of vulnerable times in fish life cycles.
  • Users can use the app to set reminders during spawning seasons to check local fish population reports or support conservation efforts. For aquaculture or research professionals, the app could track vitamin B1 levels in fish populations and alert users when spawning season approaches, prompting more frequent monitoring.
  • Establish a long-term tracking system that monitors fish population health indicators across seasons, with special attention to spawning periods. Users could log observations about local fish populations or set up alerts for scientific reports about thiamine deficiency in regional fish stocks, building a personal database of how environmental and biological factors correlate over time.

This research describes natural biological processes in fish populations and is intended for educational purposes and to inform fisheries management and conservation efforts. It does not provide medical advice for humans. While the research identifies patterns in how fish allocate vitamin B1, it does not establish definitive cause-and-effect relationships for deficiency in wild populations. Anyone involved in fisheries management, aquaculture, or fish conservation should consult with fisheries biologists and veterinarians for species-specific guidance. This study was published in 2026 and represents current scientific understanding, but future research may refine or change these conclusions.