How Fish Store Fat: Lean vs. Fatty Species
Understanding fat storage is fundamental to determining which parts of a fish contain more fat. Fish are broadly classified into two categories based on where they store their lipids: lean fish and fatty (or oily) fish.
Lean fish, such as cod, flounder, and haddock, store most of their fat in their livers. This is why cod liver oil is a well-known supplement, as it's extracted from this lipid-rich organ. The muscle tissue of lean fish typically contains less than 2% fat, and any fat content fluctuations are largely dependent on the seasonal health of the liver. This is why lean fish fillets often appear white and flaky after cooking, as the absence of intramuscular fat prevents the meat from becoming oily.
In contrast, fatty fish, including salmon, mackerel, and herring, store fat directly in their muscle tissue, in the belly flap, and under the skin. The concentration of fat in these fish can be substantial, with fillets containing up to 30% oil in some species, and this is where the highly beneficial omega-3 fatty acids are concentrated. The flesh of fatty fish often has a darker, richer color due to this fat content and seasonal changes in diet and spawning cycles can cause significant variations in fat levels.
The Fattiest Cuts: Belly and Skin
Within a fatty fish, the fat is not uniformly distributed. The richest sources of fat are consistently found in certain areas, which are often prized for their flavor and tenderness.
The Fish Belly
The belly flap, located on the underside of the fish, is consistently the fattiest part of a fish fillet. This is particularly true for fish like salmon and tuna, where the belly is a highly-sought-after cut, known as otoro in Japanese cuisine. The belly meat's higher fat content not only contributes to its richer flavor but also results in a softer, more succulent texture. When a fish is cooked, the fat from the belly section renders and moistens the surrounding flesh, making it a delicious choice for grilling or searing.
The Skin
Fish skin, especially when cooked properly to a crispy texture, is another excellent source of healthy fats. A significant portion of a fish's omega-3s are located in the layers of flesh directly beneath the skin. For many fatty fish, cooking the fillet with the skin on helps to lock in moisture and prevent the meat from drying out, while also allowing the consumer to benefit from the skin's nutrient profile. In fact, studies show that skin-on fillets contain almost twice the amount of omega-3s compared to their skinless counterparts.
The Role of Muscle Location
Even within the main muscle tissue, or fillet, the fat content can vary by location. In some species, such as Pacific salmon, the muscle near the head and nape can contain nearly twice as much fat as the muscle closer to the tail. This is an important factor to consider for both chefs seeking a specific flavor profile and for those managing their dietary fat intake.
Comparison of Fat Storage Locations
| Fish Type | Primary Fat Storage Location(s) | Example Species |
|---|---|---|
| Fatty (Oily) | Muscle, belly flap, and beneath the skin | Salmon, Mackerel, Herring, Sardines |
| Lean (White) | Liver | Cod, Haddock, Flounder |
| Semi-fatty | Combination of liver, muscle, and other tissues | Catfish, Trout, Seabass |
The Adipose Fin: Not What its Name Implies
Despite its name, which comes from the word 'adipose' meaning fat, the adipose fin is not a storage location for fat. Found in species like salmon and catfish, this small, fleshy fin is now believed to function as a mechanosensory organ that helps the fish navigate and swim efficiently in turbulent water. It's an interesting piece of fish anatomy that illustrates how scientific understanding evolves.
Conclusion
For those wondering which part of fish contain more fat, the answer depends heavily on the species and the specific cut. For fatty fish like salmon, the belly and the skin-on fillet will offer the highest concentration of beneficial omega-3s, as well as the richest flavor. For lean fish like cod, the liver is the primary fat storage organ, while the white muscle is notably low in fat. To maximize the healthy fat intake, opt for fatty species and consider eating the belly and cooked skin. However, regardless of the part, incorporating a variety of seafood into your diet is beneficial for overall health. For more information on fish composition, the Food and Agriculture Organization (FAO) offers a comprehensive guide on the topic.
