Which Fish is Classified as a Fatty Fish?

December 26, 2025 •

4 min read

According to the American Heart Association, consuming fatty fish at least twice a week can significantly benefit heart health. But what exactly is a fatty fish, and which species fall into this nutritious category? Fatty fish, also known as oily fish, are defined by their high content of beneficial omega-3 fatty acids found in their flesh.

Quick Summary

Fatty fish, such as salmon, mackerel, and sardines, contain a high concentration of heart-healthy omega-3 fatty acids throughout their tissues. This distinguishes them from leaner fish, which store fat primarily in their liver.

Key Points

High Omega-3s: Fatty fish, like salmon and mackerel, are rich in heart-healthy omega-3 fatty acids, including EPA and DHA.
Fat Storage: These fish store fat throughout their muscle tissue, unlike lean fish, which store it primarily in their liver.
Health Benefits: Regular consumption supports cardiovascular health, improves cognitive function, reduces inflammation, and benefits eye health.
Common Examples: Well-known fatty fish include salmon, mackerel, herring, sardines, and anchovies.
Considerations: Be mindful of mercury levels, especially in larger predatory fish, and choose sustainably sourced options.
Dietary Recommendation: Aim for at least two servings of fatty fish per week to reap the maximum health benefits.

Understanding the Distinction: Fatty vs. Lean Fish

Fish can be broadly classified into two groups based on their fat content: fatty (or oily) fish and lean (or white) fish. The key difference lies in where the fish stores its fat. Lean fish, like cod and haddock, primarily store fat in their livers, which is why cod liver oil is a common supplement. In contrast, fatty fish store fat in their muscle tissue and throughout their body, resulting in a higher overall fat content. This intramuscular fat is what makes species like salmon and mackerel so rich in omega-3s, which are essential for human health. The fat content in fatty fish can also fluctuate seasonally, influenced by factors like diet and reproductive cycles.

List of Common Fatty Fish

Several popular and readily available fish are classified as fatty fish, making them excellent choices for boosting your omega-3 intake. These include:

Salmon: A widely recognized fatty fish, available in both wild-caught and farmed varieties. Both are rich in omega-3s, but levels can vary depending on their diet.
Sardines: These small, oily fish are commonly sold canned but can also be found fresh. They are an affordable and potent source of omega-3s.
Mackerel: A small, oily fish known for its strong flavor and very high omega-3 content. Atlantic mackerel is particularly recommended.
Herring: Another small, oily fish that is a staple in many cuisines and provides excellent nutritional value.
Trout: Specifically, lake trout is considered a fatty fish with significant omega-3 content.
Anchovies: These tiny, flavorful fish are often used to add depth to sauces and dishes and are another concentrated source of omega-3s.
Tuna: While some varieties are leaner, certain types like bluefin tuna are rich in omega-3s. Canned light tuna is a more moderate source.

The Health Benefits of Consuming Fatty Fish

Integrating fatty fish into your diet offers a wide array of health benefits, primarily driven by their high concentration of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These omega-3s are vital for various bodily functions.

Cardiovascular Health: Regular consumption of fatty fish is consistently associated with a reduced risk of heart disease. Omega-3s help lower triglyceride levels, decrease blood pressure, and reduce inflammation, all of which contribute to a healthier heart.
Brain Function: The DHA found in fatty fish is a key component of brain tissue. It supports cognitive function, memory, and may help protect against age-related cognitive decline.
Eye Health: Studies have linked higher consumption of oily fish to a lower risk of age-related macular degeneration and improved vision.
Reduced Inflammation: The anti-inflammatory properties of omega-3s can help reduce the symptoms of certain inflammatory conditions, such as rheumatoid arthritis.
Fetal Development: Omega-3s are crucial for the development of a baby's brain and nervous system during pregnancy.

Comparison Table: Fatty Fish vs. Lean Fish


Feature	Fatty Fish (e.g., Salmon, Mackerel)	Lean Fish (e.g., Cod, Haddock)
Fat Content	Higher (6% to over 25% fat in tissues)	Lower (less than 2% fat)
Omega-3 Levels	High levels of EPA and DHA throughout the muscle	Small amounts of omega-3s, concentrated in the liver
Flavor	Stronger, richer, and more distinctive flavor due to the oil	Milder, more delicate, and less "fishy" flavor
Cooking Method	Can tolerate higher heat without drying out, suitable for grilling, baking	Prone to drying out, best suited for poaching, steaming, or sautéing
Health Benefits	Strong cardiovascular, cognitive, and anti-inflammatory benefits	Excellent source of lean protein, vitamins, and minerals

Potential Considerations: Mercury and Sustainability

While the health benefits of fatty fish are clear, it's important to be mindful of potential drawbacks, such as mercury content and sustainability issues. Larger, longer-lived predatory fish tend to accumulate higher levels of mercury over their lifespan. The FDA and other health organizations provide guidelines to help consumers make informed choices. For example, pregnant women and young children are advised to limit consumption of high-mercury fish like swordfish and king mackerel. Choosing smaller, oily fish like sardines and anchovies can minimize mercury exposure while maximizing omega-3 benefits. Additionally, being aware of sustainable fishing practices is important for protecting marine ecosystems.

Conclusion

In conclusion, a fatty fish is a species that stores a high percentage of its fat within its muscle tissue, resulting in a rich source of essential omega-3 fatty acids like EPA and DHA. Well-known examples include salmon, mackerel, herring, and sardines. These fish offer substantial health benefits, particularly for heart and brain health, distinguishing them from leaner counterparts like cod. By making informed choices, prioritizing smaller species, and preparing them healthfully, you can easily incorporate these nutritional powerhouses into a balanced and beneficial diet. The recommendation to consume fatty fish at least twice a week is a simple and effective strategy for improving overall health.

This article is for informational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

Frequently Asked Questions

A key nutritional difference is that fatty fish, such as salmon, contain high levels of beneficial omega-3 fatty acids distributed throughout their muscle tissue, while lean fish, like cod, have a much lower overall fat content.

Certain species like Atlantic mackerel, salmon, and sardines are exceptionally high in omega-3 fatty acids, with levels varying based on factors like the fish's diet and environment.

No, not all tuna is considered a fatty fish. While some species like bluefin tuna are oily, others like canned light tuna have a lower fat and omega-3 content. Albacore is in the middle.

You can often tell by their appearance and flavor; fatty fish generally have darker, oilier flesh and a richer flavor, while lean fish have lighter, milder-tasting flesh.

The American Heart Association recommends eating at least two 3.5-ounce servings of non-fried fish, particularly fatty fish, per week to support heart health.

Fatty fish, with their higher oil content, hold up well to methods like grilling, baking, broiling, or pan-searing, as they are less likely to dry out.

The nutritional value can differ, as the omega-3 content of farmed fish depends heavily on the quality of their feed. Wild-caught fatty fish tend to be higher in nutrients derived from their natural diet, though both are beneficial.