How Long Can Fish Go Without Food?

You may believe your pet fish can go a while without food, but this misconception could endanger their lives. The truth is that the amount of time a fish can go without food depends on several factors, including their environment, aquarium health, type of fish, and how well you prepare for your absence. In general, most fish can go three days to two weeks without food, but you shouldn't assume that your fish can go that long without having a caretaker there while you're away. Luckily, fish are fairly easy to care for, so whether you're away for a long weekend or a month, there are ways to ensure they're fed enough. 

So, how long can fish go without food? Many fish can fast longer than others, so let's discuss the factors that impact how long fish can go without food and how often to feed your fish. 

• Three Factors To Consider
• Preparing To Be Gone
• What About Fish In Bowls?
• FAQs
• Final Notes

Three Factors To Consider

How long do fish live when you're away? There are three main factors to consider that can impact how long a fish can go without food. 

1. Age of the aquarium setup

Your aquarium setup is your fish's environment, and whether it's new or old can affect your fish's ability to go without food. Generally, the older your aquarium, the longer your fish can be left without food because they're accustomed to it and more comfortable in their environment. Therefore, even if your fish don't eat, they're still in a safe space and among their community, providing them with ecological balance. 

However, in newer setups, the aquarium doesn't have ecological balance yet, resulting in new tank syndrome. New tank syndrome occurs when the biological filter isn't fully functional in a new setup, allowing for the accumulation of ammonia when fish are added to a new tank.¹ New tank syndrome can last up to three weeks after the aquarium is set up, requiring frequent water tests to determine when the water in the aquarium should be changed.¹

In general, fish prefer an old aquarium because they're established and have the necessary good bacteria they need to survive. However, there's also something called old tank syndrome that occurs when a sudden drop in pH kills good bacteria in the biofilter and results in high ammonia concentrations. Unlike new tank syndrome, you can't change the water because it could increase the pH too drastically, causing the ammonia to become toxic to the fish.¹

Ultimately, fish need time to adapt to their environment, so you should wait at least three weeks after giving them a new aquarium to ensure it's safe for them while you're gone. 

2. Duration of absence 

How long an aquarium full of fish can be left alone depends on several factors, but whether or not your fish can survive depends on how long you'll be gone. Therefore, the length of time you plan to leave the aquarium and fish alone will dictate how much preparation you should do before leaving. 

In general, you can likely leave your fish without food for up to three days safely, no matter the type of fish. However, if you plan to leave for an extended period of time, you'll need to prepare the tank. For example, if you're leaving for a month, you should clean the filtration system to prevent clogs and partially change the water in the aquarium. 

3. Type of fish

How often to feed fish depends on several factors, including what they eat, their age, and size. What do fishes eat? Fish can be herbivores, carnivores, or omnivores.² Herbivores eat plants and algae. These types of fish need to be fed more often to get all the nutrients they need. Meanwhile, carnivores are used to eating less often in the wild, so they can typically go longer without food. These fish, including Bettas, should be fed less often for their health, which means they don't need to eat as frequently and can often go much longer without a meal. 

The age of the fish also makes a difference. Older fish can typically survive longer than younger fish because they have more body fat. In addition, larger fish have slower metabolic rates, while baby fish need more food to help them grow.³

If you're wondering, "how long can goldfish go without food?", the answer really depends. Goldfish are  omnivores, so they can enjoy meat and plant material. Therefore, they fall somewhere in between the short fasting period of herbivores and the long fasting period of carnivorous fish. But, of course, some fish need to eat every day. Young nano fish will need to be fed daily, so you can't leave them for extended periods of time, even to go on a weekend getaway. 

All that said, it's rare for adult fish in the wild to eat every day because they have to go out and find their own food; there's no one standing above their tank dropping in a few flakes every morning. But, of course, herbivores and omnivores have easier access to food and generally get to eat more often than carnivores. 

Preparing To Be Gone

While most fish can be left for a few days as long as they're relatively healthy and not babies, you shouldn't let any fish go more than three days without food, especially since their metabolism may be used to getting food every day or so. Luckily, there are several ways to ensure your fish get taken care of while you're away. 

Use an automatic fish feeder

An automatic fish feeder is a battery-operated device that allows you to set feeding times at different intervals to ensure your fish are fed while you're away. These feeders hold the food and dispense flakes, pellets, and other dry food up to twice a day for two weeks. 

Automatic fish feeders use a timer to determine when to share food with your fish, but you must still put the right amount of food in the feeder to avoid overfeeding your fish while you're away. Remember, fish don't have stomachs, so they don't know when to stop eating. Therefore, overfeeding your fish is more dangerous than underfeeding them. Ultimately, overfeeding your fish can be fatal to them because it leads to overeating and the buildup of waste. Additionally, adding too much food to the water can lead to quality issues that make fish sick. Fish should only be fed what they can consume in three minutes.⁴ 

Unfortunately, automatic fish feeders aren't perfect, but they can ensure your fish get fed when they need to. However, if your fish decides to skip a meal or the filter stops working, it will continue to dispense food, ultimately putting them at risk of being overfed. 

Add a food block 

A food block is similar to an automatic feeder, ensuring your fish are happy and fed. They're less expensive but not as healthy for fish as an automatic feeder. Blocks work by slowly releasing the fish food by dissolving in water, and they come in several shapes and sizes to help you feed your fish at specific times during the day. However, unlike automatic feeders that you have to put food into, food blocks are made of fish food, so your fish may not be used to the new food, causing them to potentially avoid eating. 

Like automatic feeders, this option only feeds your fish for up to 14 days, so you can't be gone for more than two weeks if you leave your fish alone. Additionally, food blocks should never be used in an unfiltered aquarium because they need water circulation to dissolve properly. 

It's important to remember you should either add a food block or use an automatic feeder. Don't use both, as you could risk overfeeding your fish and upsetting the ecological balance they need to survive while you're away. Both have pros and cons, so it's up to you to figure out what you're most comfortable with. 

Get a fish sitter

The best way to ensure your fish are healthy while you're away is to have someone check in on them to ensure the aquarium filter is working properly and there are no sick fish in the tank that can infect the others. You should always write out a plan for your fish sitter to follow in case they forget how much to feed them or how to check the water quality.⁵

It's typically best to ask someone who knows how to care for fish to watch your fish because they'll already know how to test the water, fix aquarium problems, and ensure the fish are eating. However, you can leave a plan with instructions for your sitter with potential problems they'll face and solutions in case they encounter any emergencies. For example, you should have instructions for what to do if a fish dies in the tank, how to check the temperature, and who they can contact if there are issues. 

Your fish sitter should know exactly what you need them to do. If you're only going away for a few days, they may need to come once every two or three days to feed the fish and ensure they all look healthy. However, if you're going to be gone for a few weeks, they may need to add water to the aquarium and perform simple maintenance. Of course, you don't want their job to be too difficult if they don't have experience caring for fish. As long as your aquarium is working properly, your fish sitter should only need to come in and feed your fish every few days. 

If your collection of fish are healthy adults, there's no need to have someone feed your fish every day, limiting the potential for overfeeding and reducing the amount of waste that can build up in the tank. Additionally, to avoid overfeeding, your fish sitter must know how much food to put in the aquarium every day. Your instructions should be clear as to how many flakes or pellets you typically put in the tank. If possible, you can show them exactly how much or describe the exact amount of food you want to be given to your fish. 

If your fish sitter has never taken care of fish before, you should warn them not to feed them any more food than you've described in your instructions because it could be dangerous to the entire aquarium. However, if you're worried about your fish getting overfed while you're away, you can portion out their food and leave it for the pet sitter. Then, all they need to do is come into your home, grab the food, and put it in the tank. 

Clean your fish tank 

Fish should have their aquarium's water partially replaced on a weekly basis, so you should take care of this before leaving, whether or not you have a pet sitter. Additionally, you should check the pH levels to ensure everything is running smoothly. Cleaning your fish tank before you leave can also reduce the potential for toxic water due to waste buildup. While your filter should take care of removing waste, it can break while you're away, so starting with clean water can improve your fish's odds of survival if something were to happen to the filter while you are gone.

Do a trial

If you truly want to know how long fish can go without food, you can do a trial run of your time away. Consider how long you'll be away from your fish. Even if you have a pet sitter, it's unwise to stop taking care of your fish for more than two weeks because they need their environment properly managed. Therefore, even if you have someone feeding your fish regularly unless they know how to take care of an aquarium, you should never stay away from your fish for too long. 

Running a trial of up to two weeks to see how well your fish do without eating can help you learn more about them and what to do while you're away. Stop feeding your fish and performing maintenance for a few days to see how they do. Of course, you should continue to monitor the aquarium and your fish throughout the week to determine if they're doing well or not. For example, if your fish look sickly or the aquarium has waste buildup on day five, you'll know you can only leave for a period of up to five days. 

You can also choose to do a trial with an automatic feeder or food block to ensure they're effective methods for feeding your fish. If you notice waste buildup with a food block but not the automatic feeder, it's possible the food block is feeding your fish too much. However, in any case, you should always have someone who can come check on the fish every three days and give them a little bit of food to ensure you come back to a healthy tank. 

What About Fish In Bowls?

Avid fish owners know that you should never keep fish in a bowl because it's not a healthy environment for them. Unfortunately, many people keep their fish in bowls, including goldfish and bettas, because they seem easier to maintain than aquariums. However, fish bowls actually require more maintenance if you want to keep your fish healthy. 

Since fish bowls don't have filters, you'll need to clear the bowl and the water more often since there will be a buildup of waste.⁶ Additionally, bowls are less stable environments because there's no filtration and more rapid water fluctuations. They also restrict oxygen levels because they're often filled all the way up, which can restrict the gas exchange, causing fish to suffocate.⁶ Therefore, what's actually best is to fill the bowl only about halfway, but that leaves the fish with very little room to swim around. 

If your fish is in a bowl, you shouldn't leave them alone for an extended period of time because bowls require more maintenance. Since they don't have filtration or a way to manage the temperature, you'll need to spend more time caring for your fish's environment. Since your fish bowl doesn't have filtration, you'll need to partially change the water every day or every other day to prevent toxins from waste from building up. Additionally, any food your fish doesn't eat can decay in the water, causing it to become toxic. 

Fish bowls are generally bad for fish because there's no filtration or way to manage the water temperature. Since they also require more maintenance, you should never leave your fish alone in a bowl for more than a day or two. Therefore, a vacation is out of the question if you plan to keep your fish in a bowl instead of transferring them to a proper aquarium. 

FAQs

How do I feed my fish when I go on vacation?

There are several ways to feed your fish when you go on vacation, including using an automatic feeder or food block. However, the best way to ensure the health of your fish while you're gone is by getting a fish sitter who can feed your fish and check the tank to ensure they’re happy and healthy. 

Do you have to feed fish every day? 

It's better to underfeed your fish than to overfeed them, so most fish do not need to be fed daily. However, some fish should eat daily, depending on their age and metabolism. You can check with a vet if you're unsure how often to feed your fish. 

How many days can fish survive without food?

How long a fish can survive without food depends on several factors, including the health of the aquarium and the type of fish. For example, carnivores can go longer periods without eating than herbivores. If you're unsure how long your fish can go without feeding, you can ask someone at the aquatic store since they usually employ fish enthusiasts who can tell you everything you need to know about feeding your fish. In addition, some vets specialize in treating fish, and you may be able to consult them about your pet fish's health. 

Final Notes

Fish are low-maintenance pets, but they're not no-maintenance pets. Fish are relatively easy to care for compared to cats and dogs, but that doesn't mean they should be left without food for an extended period of time. Most fish do well without food for up to three to five days, but that doesn't mean it's necessarily good for them. 

Depending on several factors, like your tank, how many fish you own, and what type of fish you have, you may be able to leave your fish without food for up to seven days. However, that's not recommended since it could be dangerous for them. While you can run a trial to see how your fish do fasting for certain intervals of time, it's typically best to hire a pet sitter or use an automatic feeder or food block when you plan to leave your fish for more than five days. Having a sitter is always best because it means having someone to look after them and catch any problems that may arise. 

Of course, before you leave your fish alone for more than a few days, you must prepare the tank and ensure you have a way to feed them. If you're worried about the health of your fish before you leave or after you come home, talk to a telemedicine for pets provider like Dutch.

With Dutch, you can show us your tank ahead of time and ask for specific advice, such as "how long can fish go without food?" to ensure they'll thrive while you're away. Dutch is available for pet parents of all types, allowing you to get the advice you need to care for your pet, get prescriptions fast, and have peace of mind knowing there's a vet who can help you manage your pet's health issues. Try Dutch virtual care today.