Arielle Cruz
Preserving a dead fish in alcohol is one of several methods used to keep a fish's body intact after death. Other methods include freezing, pickling, microwaving, and injecting formalin. While alcohol preservation can effectively maintain a fish's shape and DNA, it may also cause dehydration, brittleness, and discolouration. Formalin, a clear liquid made by dissolving formaldehyde gas in water, is an alternative that prevents decomposition by creating links between proteins in the animal's tissue. However, it may not be suitable for public display due to hazardous fumes. In the case of the four-metre-long blue marlin at the Natural History Museum, scientists chose to first fix the fish in a formalin solution and then store it in glycerol, a compound that poses no threat to visitors.
| Characteristics | Values |
|---|---|
| Preservation method | Alcohol, Formalin, Vinegar, Salt, Epoxy, Glycerol |
| Alcohol concentration | 70% for preservation, 95% for fixation |
| Alcohol type | Ethyl alcohol, Methylated spirit |
| Formalin use case | Large fish, Long-term storage |
| Alcohol impact on fish | Dehydration, Loss of colour, Brittle texture |
| Formalin impact on fish | Poor penetration into tissues, Loss of colour |
| Glycerol impact on fish | Expansion of fish, Increased colour intensity |
| Fish preparation | Belly slit, Injection of formalin |
| Storage | Freezer, Formalin fixation, Glass jars, Tanks |
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What You'll Learn
Using rubbing alcohol to pickle the fish
While it is possible to preserve a dead fish using alcohol, it is important to note that alcohol will dehydrate the fish, make it brittle, and remove much of its colour. If you still wish to proceed, here is a step-by-step guide on how to use rubbing alcohol to pickle a fish:
Step 1: Prepare the Fish
Firstly, ensure the fish is dead and frozen. It is recommended to freeze the fish for at least 48 hours to kill off any parasites. Thaw the fish and cut it into small, manageable pieces.
Step 2: Brine the Fish
Create a brine solution by mixing plain, non-iodized salt and white vinegar in a container. For each quart of fish, use 5/8 cup of salt and enough vinegar to cover the fish (approximately 2 cups). Stir the solution and completely submerge the fish pieces in it. Refrigerate this mixture for 5 days, stirring once daily.
Step 3: Wash and Prepare the Fish
After 5 days of brining, remove the fish from the brine and wash it thoroughly with cold water, rinsing twice to ensure all the salt is removed.
Step 4: Create the Pickle Solution
Prepare a pickle solution by heating vinegar, granulated sugar, and pickling spices in a pot. For each quart of fish, use 1 1/4 cups of vinegar, 7/8 cup of sugar, and 4 teaspoons of pickling spice. Heat this mixture until it almost reaches a boil, then allow it to cool completely.
Step 5: Layer the Fish and Solution
Obtain a glass jar and start layering. Begin with a layer of fish pieces, followed by a layer of sliced onions and bell peppers. Repeat this process until the jar is tightly packed with alternating layers of fish and vegetables.
Step 6: Add Rubbing Alcohol
To preserve the fish using rubbing alcohol, ensure you are using 70% isopropyl alcohol (rubbing alcohol). Pour the cold pickle solution over the layered fish until everything in the jar is completely covered.
Step 7: Refrigerate and Store
Refrigerate the jarred fish for at least 5 more days. After this period, the pickled fish will be ready for consumption or display. Store the pickled fish in the refrigerator, ensuring the fish remains covered in the pickling solution.
Please note that while this method may preserve the fish for several years, it will likely cause the fish to shrivel and lose its colour over time. Additionally, always exercise caution when handling chemicals like alcohol and formaldehyde, and ensure proper ventilation during the process.
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Preparing the fish for preservation
For small fish, a simple method is to first soak the fish in vinegar for 24 hours. After removing the vinegar, place the fish on a piece of paper and cover it with salt, leaving it for 30 minutes. Then, microwave the fish for one minute at full power. Finally, place the fish in the freezer for 24 to 48 hours. This method is not recommended for larger fish, as it may not penetrate the body cavity and prevent spoilage.
For larger fish, it is recommended to use a chemical fixative such as formalin (a solution of formaldehyde gas in water) or ethanol. Formalin is a preferred choice for large specimens as it effectively stops the flesh from decomposing. However, it can be difficult to create aesthetically pleasing preservations due to its poor penetration into tissues. To improve penetration, it is recommended to inject formalin directly into the body cavity or make a slit in the belly of the fish. After fixation, the fish should be washed in several changes of water over a period of two to three days to remove any residual formalin.
Another method for preserving large fish involves using glycerol, a compound that poses no threat to visitors in a public display setting. The fish is first fixed in a formalin solution and then transferred to a tank of glycerol. Over time, the concentration of glycerol is gradually increased, allowing it to penetrate the body of the fish. This method helps the fish regain its natural shape and may also enhance the intensity of any remaining colours in the skin.
It is important to note that alcohol preservation can be used for long-term storage, but it may cause dehydration, brittleness, and loss of colour. To mitigate this, the alcohol concentration should be raised slowly, and the fish should be handled carefully to ensure a good posture during preservation.
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Using formalin to preserve the fish
Formalin is a clear liquid made by dissolving formaldehyde gas in water. It is a popular choice for preserving large fish. It creates links between proteins in an animal's tissue, which stops the flesh from decomposing. Formalin is also used to control parasitic infections on the external surfaces (skin, fin, gills) of fish. It is extremely effective against most protozoans as well as some larger parasites, such as monogeneans.
To preserve a fish using formalin, start by killing the fish with a chemical anesthetic such as MS-222. If possible, remove a small piece of muscle tissue or a fin clip and place it in a small vial of 95% ethanol for genetic preservation. Next, create a solution of formalin by mixing one part commercial formaldehyde and nine parts water. If the fish is larger than a few inches, cut the belly to allow the chemical to penetrate the insides of the fish. Alternatively, use a syringe or hypodermic to inject the formalin into the body cavity and muscle tissue. Place the fish in a container and fill it with the formalin solution. Ensure the fish assumes a good posture in the solution as it will remain that way once fixed. Leave the fish in the formalin for at least three days, with larger fish requiring up to a week or more.
After the fish has been fixed in formalin, it needs to be washed. Soak the fish in water for a couple of days to remove the formalin. Finally, place the fish in a container of 70% alcohol for long-term preservation.
It is important to note that formaldehyde, the active ingredient in formalin, is hazardous and should be handled with care. Additionally, formalin should always be disposed of according to strict state guidelines and should not be poured down the drain.
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Using ethanol to preserve the fish
Ethanol is a suitable preservative for fish, although it is not a fixative and will not penetrate tissue as well as formalin. To preserve a fish using ethanol, you will need access to 70% ethanol or alcohol, as well as a container to store the fish.
Firstly, it is recommended to kill the fish using a chemical anaesthetic such as MS-222. If you wish to preserve the fish's genetic information, you should take a small piece of muscle tissue or a fin clip and place it in a small vial of 95% ethanol.
Next, you should prepare the fish for preservation by either slitting the belly of the fish with a sharp knife or injecting it with formalin, a solution made from one part formaldehyde and nine parts water. This allows the fixative to enter the body cavity and preserve the fish. The fish should be left in the formalin solution for several days, with larger fish requiring a longer period of time.
After the fish has been fixed, it should be removed from the formalin solution and placed in a container of water for a day to wash out the formalin. Finally, the fish can be transferred to a container of 70% ethanol for long-term preservation.
It is important to note that ethanol preservation may cause the fish to shrivel and lose its colour over time. Additionally, the ethanol must be of sufficient strength and quantity to effectively preserve the fish.
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Alternative preservation methods
There are several alternative methods to preserve a dead fish. One method is to use formaldehyde, which is a type of alcohol, to fix and preserve the fish. This method can be done by injecting the formaldehyde into the fish or cutting the belly of the fish to allow the chemical to enter and preserve everything. The fish is then placed in a container of water to soak out the formaldehyde and then transferred to a container of 70% alcohol for long-term preservation.
Another method is to use a combination of formalin and glycerol. Formalin is a clear liquid made by dissolving formaldehyde gas in water, which creates links between proteins in an animal's tissue and prevents decomposition. Glycerol is a compound that helps the fish expand and return to its natural shape, and it may also intensify the colours that are left in the skin. This method was used to preserve a four-metre-long blue marlin at the Natural History Museum.
Additionally, you can also use a super worm to preserve the fish. It will look mummified but will be preserved.
Other alternative methods include freeze-drying, using silica gel, pickling with rubbing alcohol, or a combination of vinegar, salt, and microwaving.
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Frequently asked questions
First, you must use a chemical anesthetic to euthanize the fish. Then, depending on the size of the fish, you can either inject it with formalin or make a small incision in its belly and soak it in a formalin solution for several days. This will prevent the fish from decomposing. Afterward, you can transfer the fish to a container of 70% alcohol for long-term preservation.
Formalin is a clear liquid made by dissolving formaldehyde gas in water. It penetrates animal tissue and creates links between proteins, which prevents the flesh from decomposing.
Alcohol preservation is useful because it can maintain the DNA of the fish. However, alcohol is prone to evaporation and may cause the fish to become brittle, shrivelled, and discoloured.
