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-- S p o i l a g e o f f i s h --
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| Q 1. | ||
| What causes fish to spoil? |
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| Q 2. | ||
| Does the light of the moon damage fresh caught ocean fish in any way if left exposed to full moon light? I will appreciate an early reply as this has become highly controversial at a neighborhood bar. |
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| Q 3. | ||
| Is there a chemical which can be applied to fish which will lengthen the period before spoilage begins? |
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| Q 4. | ||
| Is it true that fish will spoil more quickly under the light of the moon than when there is no moonlight? Is there anything in the moon's rays that would cause a more rapid spoilation than otherwise? |
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| Q 5. | ||
| In fishing, I am often out in my boat from four to five hours and sometimes longer. In that time, the fish I catch are placed in a container filled with water and will not be cleaned until I come into the dock. Can you give me an estimate as to how long after fish are caught, they can be safely held before drawing and still be edible? |
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| Q 6. | ||
| While fishing I am often in my boat for five or more hours. The fish I catch are placed in a water-filled container and cleaned after I get back. How long will fish remain fresh before they are cleaned? |
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| Q 7. | ||
| I have heard that people have been poisoned by eating lobsters that were allowed to die before being cooked. I have also heard that lobster deteriorates very rapidly. Could you instruct me on the above points and also answer the following questions? What happens when a live lobster is frozen? Will lobsters live in fresh water? Is it better to boil the entire lobster, or to remove and boil just the tail? If so, why? |
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| Q 8. | ||
| I would appreciate it if you would tell me what makes fish smell "fishy." |
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| Q 9. | ||
| For many years, I have heard the statement that if a lobster is allowed to die slowly it will "poison" its flesh and be unfit to eat. Is this true and, if so, what is the cause? |
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| Q 10. | ||
| When I catch fishes this summer, how should they be preserved for the hot trip home in the car? |
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| Q 11. | ||
| How fast do bacteria grow on unrefrigerated seafoods? |
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| Q 12. | ||
| I have heard experienced fishermen say that if freshly caught fish are rained on, the fish will spoil. Is this true? |
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| Q&A 1. | What causes fish to spoil? Coral Gables, Florida |
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| To answer this question it is necessary to define the term enzyme. An enzyme is a chemical that rather slows down or speeds up chemical changes. Upon death, certain enzymes which are responsible for the building up of the body in life are inactivated and those enzymes responsible for the breaking down of body cells take over. When the walls of body cells are broken down by this enzyme activity the proteins and fats that were present are now free to escape. Further enzyme activity reduces the complex chemical form of these substances to simpler forms, some of which are evil smelling decomposition products. At the same time, bacteria that are normally kept in check in the live animal now thrive on the proteins and fats. With the increase of the bacterial flora, decomposition of the animal is rapid. Spoilage is therefore the result of a combination of two factors--enzyme activity and bacteria. The growth of bacteria and the activity of enzymes can both be retarded by low temperatures. |
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| Q&A 2. | Does the light of the moon damage fresh caught ocean fish in any way if left exposed to full moon light? I will appreciate an early reply as this has become highly controversial at a neighborhood bar. Miami, Florida |
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| This is a very interesting question, but very difficult to give an answer of a definite nature. There is no scientific evidence that moonlight in any way will speed up the spoilage rate of fish. The absence of light is beneficial to the growth of bacteria located on the surface of the fish since the ultraviolet rays of the sun destroy any germs that they come in contact with. However, it is neither the light from the sun nor the moon, but rather the heat generated by the sun that increases the rate of spoilage. With an increase in temperature (up to a certain degree) the metabolism increases. This increase in metabolism enables the bacteria to carry on their functions at an increased rate. Thus it is not light but heat that causes spoilage. |
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| Q&A 3. | Is there a chemical which can be applied to fish which will lengthen the period before spoilage begins? West Palm Beach, Florida |
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| Handling practices aboard fishing vessels, at the docks, and during the process of distributing the catch have the greatest influence on the keeping qualities of fish, although various chemicals have been used with some degree of success. Several substances are considered useful in the control of bacterial contamination and slime in fish. A mixture of benzoic and fumoric acid has been used as a dipping solution or has been incorporated in the ice. Lemon juice has also been employed to control bacteria and rancidity in fish. Several substances which contain chlorine are useful for sanitizing equipment and for washing fresh fish. Several antibiotics have been shown to increase storage life of fresh fish, but the use of these chemicals is not yet permitted by the U.S. Food and Drug Administration. |
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| Q&A 4. | Is it true that fish will spoil more quickly under the light of the moon than when there is no moonlight? Is there anything in the moon's rays that would cause a more rapid spoilation than otherwise? Daytona Beach, Florida |
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| There is no scientific evidence to back a claim that the rays of the moon have a harmful effect of the keeping qualities of fish. Very frequently the observations that fish spoil faster when exposed to the moonlight are made hastily by people who lack technical training. It is probable that, had observations been made on all factors, it would have been found that the causes of spoilage were the temperature, the sanitary conditions of the holds, the length of storage, or even the method of catching the fish, or some other factor. |
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| Q&A 5. | In fishing, I am often out in my boat from four to five hours and sometimes longer. In that time, the fish I catch are placed in a container filled with water and will not be cleaned until I come into the dock. Can you give me an estimate as to how long after fish are caught, they can be safely held before drawing and still be edible? Bradenton, Florida |
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| It is not possible to be specific about the time fish will remain edible after holding in water at the temperature in your area. For one thing the level of acceptability of freshness is an individual matter and varies greatly. Spoilage depends mostly on temperature, which controls to a large extent the bacterial and autolytic (enzyme) breakdown, and fish should be kept as cold as possible. The rate of spoilage also depends on the kind of fish taken, on the sanitary condition of the boat, and the amount of food in the gut. If possible you should carry a small amount of ice and keep the fish as cold as possible. Failing this, keep them under wet sacking or other material. The evaporation from the sacking will help keep the temperature down a little. You should not keep fish in water, as it warms up rapidly and you should clean the fish quickly and sprinkle a little salt in the body cavity. |
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| Q&A 6. | While fishing I am often in my boat for five or more hours. The fish I catch are placed in a water-filled container and cleaned after I get back. How long will fish remain fresh before they are cleaned? Bradenton, Florida |
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| It is not possible to be specific about the length of time fish will remain fresh. Spoilage depends largely on temperature, which controls to a large extent the bacterial and autolytic (enzyme) breakdown, so fish should be kept as cool as possible. The rate of spoilage also varies with species and the amount of food in the gut. If possible you should carry ice and keep your catch as cold as possible. If you have no ice, keep fishes caught under wet sacking or other material. The evaporation from the sacking will help keep the temperature down. You should not keep dead fishes in water, as it warms up rapidly. It is best to clean your catch right away and sprinkle salt in the body cavity. |
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| Q&A 7. | I have heard that people have been poisoned by eating lobsters that were allowed to die before being cooked. I have also heard that lobster deteriorates very rapidly. Could you instruct me on the above points and also answer the following questions? What happens when a live lobster is frozen? Will lobsters live in fresh water? Is it better to boil the entire lobster, or to remove and boil just the tail? If so, why? Torrance, California |
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| The spiny lobster is not poisonous if allowed to die before it is cooked. Most lobsters sold commercially are killed and frozen before cooking. It is true that lobsters and other crustaceans spoil rapidly after death, and this is why most commercial buyers insist on receiving them alive. If the lobster is "headed" before or soon after death, the tail meat will keep longer than it would if the head were left on. This is because the so-called head includes the thorax, in which most of the viscera and the gills are located, and these spoil much more rapidly than the muscle of the tail. When a live lobster tail is frozen, deteriorative changes due to bacterial and autolytic (self-digestive) chemical action are greatly inhibited, and a better product results. Lobsters die very quickly in fresh water. Whether to boil lobsters whole or tails only is simply a matter of taste. Some people prefer the flavor of the whole boiled lobster, but the two methods are equally safe. |
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| Q&A 8. | I would appreciate it if you would tell me what makes fish smell "fishy." Valley Center, California |
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| The flesh of fresh fish is practically odorless and any odor they may have is the result of environmental factors, such as recent meals and clinging external materials. Fish begin to smell fishy when they begin storage deterioration, in which bacterial and enzymatic action releases oxidized fats and various amines. These do have noticeable odors. |
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| Q&A 9. | For many years, I have heard the statement that if a lobster is allowed to die slowly it will "poison" its flesh and be unfit to eat. Is this true and, if so, what is the cause? Altadena, California |
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| No, the statement is not true. It is true, however, that a lobster left whole will spoil faster from seepage of intestinal fluids into the meat and bacterial action than a lobster that has been de-tailed. Proper refrigeration is also necessary, of course, to prevent bacterial spoilage. |
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| Q&A 10. | When I catch fishes this summer, how should they be preserved for the hot trip home in the car? Brownsville, Texas |
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| For safe edibility and superb flavor, proper care of a catch begins with immediate removal of the viscera and gills and thorough washing to remove slime, mud, and blood. Next, the belly cavity should be dried thoroughly and packed with ice. Then, each fish should be packed separately amidst ice in a chest. As the ice melts during the trip home, the water should be drained. If dry ice is used, it is important to remember that it gives off carbon dioxide, which will replace the oxygen in the car even if the dry ice is in a chest in the trunk. Therefore, it is essential to keep car windows open for ventilation. These and other safety tips for recreational fishermen are offered on a card published by Sea Grant, University of Washington HG-30, 3716 Brooklyn Avenue, N.E., Seattle, Washington 98105. |
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| Q&A 11. | How fast do bacteria grow on unrefrigerated seafoods? Winston-Salem, North Carolina |
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| One bacterium on a piece of seafood will duplicate itself by dividing, in less than 20 minutes under ideal growth conditions (food, water, and proper temperature). Those two bacteria will divide in the next 20 minutes, resulting in four bacteria, and so on. Thus, if ideal growth conditions continued for eight hours, for example, one bacterium has the potential of growing into more than 16 million bacteria. All raw seafoods contain an initial amount of bacteria, but growth of these bacteria can be retarded. As recommended in Marine Advisory Bulletin MAP-22, Bacteria and Seafoods by Otwell and Koburger, the containers, utensils, and surfaces used to process raw seafoods should be thoroughly cleaned and sanitized before being used for cooked products. Seafoods should be refrigerated at between 32 degrees Fahrenheit and 40 degrees Fahrenheit. Frozen foods are typically stored at 0 degrees Fahrenheit but, for seafoods, the authors recommend -20 degrees Fahrenheit or below. Although it is written primarily for workers in the seafood-processing industry, Bulletin MAP-22 describes precautions that should be taken in the home kitchen as well. One copy is free upon request from the Marine Advisory Program, University of Florida, G022 McCarty Hall, Gainesville, Florida 32611. |
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| Q&A 12. | I have heard experienced fishermen say that if freshly caught fish are rained on, the fish will spoil. Is this true? Guanica, Puerto Rico |
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| Fish are likely to spoil if they are held under conditions in which they might get rained on. The primary cause of fish spoilage is bacteria, which occur naturally on the gills and skin and in the gut of fish. Bacteria reproduce in warm, moist conditions. They do not normally harm live fish, but do spread into the flesh of dead fish quickly through wounds and bruises. Bacteria are inhibited from growing by freezing, cooking, or by conditions that reduce moisture, such as salting. Washing of freshly caught fish, with fresh water or salt water, is good for the catch because it rinses away some of the bacteria from the skin and gills, and from the abdominal cavity if the fish has been gutted. However, fish must be preserved as quickly as possible by some method such as freezing, salting, drying, smoking, or canning. If the catch is left exposed, additional water could promote the growth of bacteria by increasing the moisture content, raising the temperature, or washing bacteria into breaks in the skin of the fish. This may be the reason fishermen find that their catch spoils faster if it has been rained on. The best way to temporarily preserve freshly caught fish is to gut and rinse them and then store them in a clean, insulated fish box with a concentrated, iced saltwater brine. Once the fish are taken to shore, they should be processed by freezing or one of the other methods mentioned above. |
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Rosenstiel School of Marine & Atmospheric Science Library
University of Miami, FL USA 4600 Rickenbacker Causeway, Miami, Florida 33149 Phone: 305 421 4060 Fax: 305 421 9306 E-mail: libcirc@rsmas.miami.edu |
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