How long can fish live in a bag?

If you are new to fish farming, you may be surprised to see your pet placed in a plastic bag for the trip home. This is by far the most common method of transportation, but how long can fish stay in the bag at the pet store and what is the best way to move them into their permanent home?

How long can fish stay in a plastic bag?

We’ve all brought home new fish from the pet store in those heavy-duty plastic bags filled with water and air, but have you ever wondered how long fish can survive in a bag? It depends on a number of factors, but in general, fish can survive in a bag for about 7-9 hours comfortably, and possibly up to two days.

However, there is more to this method of transportation than meets the eye. Pet stores usually fill their bags with about ⅓ of water and fill them with oxygen instead of room air. If you’re trying to duplicate this method at home, there are a few things to keep in mind before you pack your fish.

Factors to consider when keeping fish in bags

Transporting fish in plastic bags is not a new method; has been the standard for over 30 years. Breeders ship fish to stores in these bags, and if you order fish online, this is how they will arrive at your mailing address. How long you can keep fish in a bag depends on multiple factors, including:

  • The size of the bag.
  • Whether the bag is filled with oxygen or air.
  • The size and number of animals in the bag.
  • conditions during transportation.

Why is oxygen so important?

Like us, fish require oxygen or O2 to breathe (breathe) and their gills are adapted to absorb oxygen from the water they swim in. Some fish, like bettas, also have an organ that allows them to breathe air above the waterline, so they can survive longer in stagnant water.

Hypoxia (lack of oxygen) can be a real problem in aquariums, which is why we use filtration systems and devices like air stones to keep O2 levels high in our tanks. When fish are kept in closed containers, it doesn’t take long before they have essentially used up all the oxygen in the water and air and begin to suffocate.

Fish survive longer in bags filled with oxygen than air

How much O2 does the air around us contain? You might be surprised to learn that air at sea level is actually 78% nitrogen and only 21% oxygen, and as you gain altitude and lose atmospheric pressure, the O2 molecules get further apart, so it becomes more difficult to breathe without gasping.

  • In Denver, Colorado (a mile above sea level) the air effectively feels like it only contains about 17% oxygen.
  • The top of Mount Everest (5.5 miles above sea level) only has 33% of the oxygen available at sea level.

If you pump regular air into your fish’s bag to transport it, they will begin to feel the effects of hypoxia. about 4 times sooner than if you filled it with 100% oxygen. That’s why pet stores and aquatic stores use pressurized O2 to fill their bags instead of pumping them out with room air.

Several fish in a single bag consume more oxygen

Larger fish consume more O2 than smaller fish, and multiple fish will consume the oxygen in a sealed bag faster than a single fish. If you’re relocating your aquatic community, it’s best to give each fish its own bag so they don’t compete with each other for oxygen.

If the trip is short, you can bag several fish together as long as they are of similar size and there is enough space, but it could be stressful for them if you experience any delays in setting up the new tank. Since you probably won’t have an O2 tank on hand to fill your bags and will have to use air, it’s safer to give them each their own container.

Larger bags can carry more oxygen

You may have noticed that pet stores only fill fish transport bags about ⅓ of the way with water, so more than half of the bag is filled with oxygen. As the fish consume the O2 dissolved in the water, more of the air in the bag is absorbed. Filling the bag with pure oxygen helps maintain comfortable O2 levels for your fish.

Larger bags can hold more oxygen than smaller ones, assuming you’ve used the same ratio of water to air. Placing a small fish in a large bag will prolong the period in which it can be kept safely and comfortably sealed inside. Using a large container can also help compensate for the inability to fill the bag with pure O2 at home.

Bags and containers to transport fish

What type of container should you use to transport your fish and what type of container should you choose?

zip lock bags

Ziplock bags seem like a convenient way to transport fish, but I really don’t recommend using them if you can find a better alternative. The bags are not very sturdy and can easily leak, and are too narrow at the bottom to comfortably hold most types of fish. Your fish is likely stressed and tight in a tight seal.

If you need to use ziplocks, I recommend limiting the amount of time your fish is in the bag to about 30 minutes. You won’t be able to fill them with as much air as other types, so your fish won’t be comfortable with them for long. Always use a new bag and recycle it when you’re done; It’s not really a good idea to reuse the bag afterwards.

Polyethylene bags or “polyethylene”

Professional fish farmers and aquatic shops prefer to transport fish in the heavier plastic bags known as “Poly Bags”. ” Made of polyethylene, they are usually 1.5 to 3mm thick and have a wide, fairly flat bottom when filled. They are the ideal shape for transporting fish over long distances.

Polyethylene bags are typically 3-4 times as long as they are wide, allowing you to pump the maximum amount of air or oxygen into the bag. Once the bag is filled and sealed tightly with a rubber band, you can tape the bottom corners for added security and turn the bag on its side (see Transport below), and it shouldn’t leak.

hard plastic containers

It can be tempting to use a hard plastic container to transport your fish as it seems like it would be the most sturdy option, but there are a number of reasons why it’s not the best option:

  • Both Tupperware-type hard plastic and thinner reusable containers are relatively expensive (compared to poly bags) when new.
  • You should not reuse an old plastic container for transporting fish, because plastic absorbs odors and chemicals (such as soap and cleaners), which could leach into your fish’s water.
  • You can’t cover a hard plastic container with oxygen or air, so you’re limited to only the O2 in the headspace left after adding fish to the water.
  • You cannot easily acclimate your fish to their new aquarium if they are in a hard plastic box and you will likely have to move them to a plastic bag anyway, increasing their stress level and the chance of injury.

I do not recommend transporting fish in hard, sealed containers, even for a short period of time. It’s risky. If you have no other options, be sure to use new containers and give each fish its own, and throw them away when you’re done. There is always the possibility that your aquarium is harboring a zoonotic disease and you don’t want to share it.

How to improve the experience of your fish during transport

Moving is stressful for fish, no matter how careful you are, so what are ways you can make things easier for your aquatic friends while you’re transporting them home?

How to transport bags of fish

The best way to transport a bag of fish in your vehicle is in an insulated container, such as a small cooler (no ice, of course):

  • This prevents the bags from being dumped in the car, which could injure or stress the fish.
  • It also prevents a sudden drop or rise in water temperature.

Inside a sealed bag or container, the only movement of the water comes from transport agitation, so it can take time for the O2 to dissolve from the air into the water. Placing the bag on its side increases the surface area of ​​the water, allowing more O2 to be absorbed. This could come in handy for longer trips.

I always make sure the corners of the carry bags are taped down, so a fish can’t accidentally get caught if the bag moves. I once lost a fish due to such an accident during transport, so I always take extra precautions to prevent it from happening again.

How to transfer fish from the bag to the aquarium

My method for moving fish from their shipping container to their new aquarium is a bit different than what most online guides recommend. There are a few things I learned acclimating fish to a new tank from working at an aquarium store, and I am going to share these insider secrets with you!

Why do we acclimate fish to a new tank?

First, why do we acclimate the fish instead of just throwing them directly into the new tank? The stores say it’s to allow the fish to adjust to different water temperatures. Otherwise, the temperature change could shock your fish. This is true but it also misses a bigger point.

Water temperature is just one parameter among many your fish will have to adapt to when they change homes; they may also have to get used to a different pH and hardness level of the water. Floating a sealed bag of fish in their tank to acclimate them to the temperature will not help them adjust to the other differences.

Ideal way to acclimatize a bag of fish

Instead, I float the bag for 20 minutes and then add some water from my aquarium. Then I wait and add some more. After several rounds of this for an hour, I carefully use a fishing net to catch the fish in the bag and transfer them to my tank. This gives your fish time to adjust to the new parameters gradually and is much less stressful.

There is another benefit of this method. I don’t add water from the bag back to the larger tank and dispose of it instead. This helps prevent the introduction of diseases and parasites to my aquarium. Sure, my new fish might as well carry them, but it has definitely reduced Ich outbreaks and infections in my populations.

Acclimatizing fish to a new tank: step by step

It typically takes about an hour to acclimate a bag of fish from start to release using this slower, more gradual method. You will also need a clip or some way to prevent the bag from slipping into your tank during the acclimatization process once it has been opened:

  1. Let the sealed plastic bag(s) float in your tank for about 20 minutes.
  2. Open the bag and add ½ to 1 cup of water from your aquarium.
  3. Clip or secure the open bag to the side of your tank (so it doesn’t slip or float up and release the fish early).
  4. Wait 20 minutes and add another ½ to 1 cup of aquarium water to the bag, and then wait another 20 minutes before releasing.
  5. To release your hardened fish, use a small fishing net to catch them in the bag or gently pour the bag into a large net held over a bucket.
  6. Carefully release your new fish into your tank and discard any remaining water in the bag or bucket.


While fish properly packaged in an oxygen-filled bag can survive up to two days, they become increasingly stressed as debris accumulates in the water, so transport and acclimate your new pets as soon as possible. We’d love to hear your thoughts on fish transport, so leave a comment below or join our aquatic community on social media.

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