The aroma is of the sea, fresh from the sea. When fish are killed, bacteria and fish enzymes convert TMAO into trimethylamine (TMA), which gives off the unmistakable fishy stench. This chemical is particularly prevalent in the flesh of cold-water surface-dwelling fish such as cod. Smoked fish also tends to have a strong smell due to the presence of trimethylamine.
In addition to being rotten eggs on land, sulfur compounds can be found in many different types of seafood: shellfish contain high levels of sulfides, while fish contain higher levels of polysulfides.
The main source of these chemicals is the bacterial action that takes place at sea after a large fish has been caught. The decaying body of the fish produces more bacteria, which in turn produce more odoriferous substances. As well, when fishing for larger fish, by-products of the catch (the blood, guts, and skin) also decay at sea and release more odoriferous substances.
Even before it reaches our plates, seafood has an odor. This is because fish and shrimp decompose quickly at room temperature. They should always be bought as soon as possible after they're caught to limit their exposure to oxygen and sunlight, which cause further decomposition. The more fish that a fisherman catches, the more likely it is that some will stink. However, even if a lot are caught, that doesn't mean that all will smell.
Trimethylamine oxide (TMAO) is commonly used by ocean fish for this function. When fish are killed, bacteria and fish enzymes convert TMAO into trimethylamine (TMA), which emits the distinctive "fishy" stench. There are two techniques to decrease the odor. If the fish is to be cooked, go ahead and cook it first and then bury it in some soil or compost. The bacteria that cause the odor will die when exposed to heat, so cooking the fish removes it as a source of pollution.
The second method involves taking advantage of this natural process and using it as a way to remove the odor of fish that have been buried in the ground for several months or more. This can be done by digging them up and putting them in a bin filled with an oxygen-rich environment; this will allow more of the TMAO to turn into TMA, reducing the amount of odor that escapes when they're re-buried.
In addition to being an important part of their defense system, fish also use odors to communicate with each other. For example, when a predator approaches a school of fish, they will often release chemicals into the water to alert others of the danger. The fish then swim away from the threat in order to hide from view until the danger has passed.
Fish also use odor to find food. They will search for specific smells that indicate they are close to an edible object.
As a result, cod would begin to stink sooner than, example, catfish. However, since most fish sold in markets have been frozen without being smoked or cured, their flesh does not develop any special smells.
Here are some more interesting facts about fish:
Fish are an important source of food for humans. Fish account for approximately 10% of all animal products consumed by humans.
Fish are also used in scientific experiments to study the effects of drugs and toxins on animals. The sensitivity of fish to certain chemicals makes them useful for detecting toxic substances at very low levels in the environment. For example, scientists have used fish to monitor pollutants in the water around Japan after the nuclear accidents at Fukushima and Chernobyl.
Fish are also used in clinical trials to test new treatments for diseases. Because people don't usually eat whole fish but instead use pieces of meat from different parts of the fish, it's difficult to conduct human studies with cats. Thus, researchers often use fish as a substitute for other types of laboratory animals in experiments related to heart disease, cancer, and other illnesses.
Finally, fish are important for wildlife conservation. Many fish serve as prey for larger fish and predators.
The presence of TMA in urine is an indicator of kidney disease.
TMAO is also produced by some bacteria in the digestive system of animals. This is a normal reaction to prevent other substances from being absorbed through the intestinal wall. As well as fish, people can also smell TMA if they eat meat that has not been properly cooked. The smell disappears when the meat is heated through.
In high concentrations, TMA is toxic to fish and other aquatic organisms. Fish absorb large amounts of air when swimming so have more opportunity to become disoriented with respect to gravity and temperature control. This can lead to suffocation if enough TMA enters their bloodstream.
Humans don't seem to be affected by small amounts of TMA. However, larger doses may cause symptoms such as nausea, vomiting, and diarrhea. Heated foods containing TMA may produce symptoms similar to those seen with food poisoning caused by bacteria.
The formation of TMAO occurs naturally in the body but at a slower rate. Therefore, humans produce more TMAO than fish do.
TMA may bind to water and become less volatile when exposed to acidic materials such as lemon, vinegar, or tomato. As it binds to sediment, TMA can build up in fish tanks.
When fish are cleaned before cooking, any fluid that has penetrated their skin has a chance to evaporate, allowing more TMA to form. The more TMA, the worse the smell. Fish also contain high levels of other substances that emit foul-smelling compounds upon decomposition, such as hydrogen sulfide for salmon and charr, and methyl mercaptan for trout and black bass.
The best way to avoid this problem is not to buy fish with an odorant taste or scent. However, this isn't always possible because some fish just have too strong of a smell or taste to be acceptable to some people.
Fish fillets and steaks will usually keep their smell after drying, but if you dry whole fish, you'll need to wash them first to get rid of any dirt or debris that may have accumulated during fishing season. Washing fish removes much of the surface TMA so it doesn't smell as strongly when heated.
You can also coat fish with ingredients known as masking agents.