6 Huge Reasons Why Your Saltwater Fish Are Not Eating

If you notice that your saltwater fish have stopped eating, there could be several reasons why. 

There are going to be some challenging times when maintaining a saltwater tank. 

If your fish are not eating, this can be stressful for both you and the fish.

Without a proper diet, your fish’s health will suffer and they could eventually die.

It’s not normal for a fish to stop eating. They naturally want to eat. If this happens, it’s a sign that there is something wrong. 

It’s important that you determine the reasons why your fish is not eating so you can address and fix the problems.  


Why are your saltwater fish not eating?

There are many reasons why your fish are not eating. The main ones being due to an illness or stress. Normally this is caused by poor water conditions and lack of maintenance being performed on the tank. If your tank water levels are within the proper parameters, your fish have a much better chance of staying healthy and eating won’t be a concern. 


saltwater fish not eating

1. Poor water quality

A leading cause for saltwater fish to stop eating is poor water quality.

Fish are sensitive to changes in water parameters and it’s important to maintain certain levels within a range that will keep your fish healthy.

You should test your levels on a regular basis and keep on track with water changes and routine maintenance duties. Some of the items to keep track of include PH, temperature, nitrate, phosphate, ammonia, and more.

Here is a chart to reference for water parameters.

Poor water quality will be stressful to fish and cause them to become unhealthy. A sick fish generally won’t eat.




2. Illness/disease

As mentioned, when your fish is sick, it usually will avoid eating. There are a number of illnesses that your fish can get including marine ich, fin rot, marine velvet.

Infections are also known to prevent your fish from eating. If the illness is serious enough, your fish can stop eating altogether which makes the illness worse.

Not only are they suffering from being sick, but now they won’t be getting the nutrition they need to be healthy. 


3. Stress

Stress with saltwater fish is very common. It can be caused by various reasons including poor water quality, being bullied by other tankmates, low oxygen levels, and more. 

Other reasons could be:

  • High ammonia levels
  • Low or high salinity
  • Too small tank size
  • Too many fish in the tank
  • Medications
  • Temperature fluctuations

Most times cases of mild stress can be addressed without problems. But if your fish is under severe stress levels, they can easily get sick and refuse to eat. 

If you have added a new fish recently, or even if the fish has been in the tank for a long time, check for signs of stress as this can cause the fish to not eat. 


4. Overfeeding

Another reason why your fish might not eat is due to overfeeding the tank.

Overfeeding is a huge problem and most people feed their fish too much.

If your fish are getting too much food, not only will it cause poor water quality, but the fish can get sick and stop eating.

Most fish will not eat when full and it’s important to only feed them the proper amount of food each day. 

Overfeeding can cause bloating and constipation in fish.

It’s better to feed your fish a few small meals each day. Any unwanted foods should be removed from the tank to prevent it from decaying and causing poor water quality. 

Poor water quality can cause sick fish and sick fish won’t eat. 


Read: How often to feed your clownfish (Feeding guide)

5. Wrong food

Not all saltwater fish eat the same foods. If you are providing the wrong food for your fish, chances are they won’t eat it.

Whether it’s the wrong type of food or something they do not like, it will be difficult to get them to eat it. 

You may have a fish that is a carnivore and only feeding it a vegetable diet is not a great idea. They won’t be inclined to eat that as much as meaty foods. Carnivores require a meaty diet. 

Another example is the Mandarin Dragonet. This fish will only eat live foods like copepods and trying to feed it anything else usually ends up bad. 

It’s common for these fish to starve to death due to being fed the wrong food. If you notice your fish is not eating, it’s possible that they are being offered the wrong type of food


6. Being outcompeted

If you have various fish types in your tank, it’s possible that they will outcompete each other for food. Some fish are smaller and slower than others and normally when you feed the tank, the fish will move fast and eat as much as they can.

Unfortunately, this is not a good thing for the slower fish in the tank. If these fish are being bullied or simply faster than others, they can take all the food leaving the others with none.

It’s natural for fish to compete with each other for food. Feeding a tank full of tangs can get quite interesting.

You need to ensure that the slower and less timid fish in the tank are getting properly fed. 

Marine Depot Aquarium Supplies

What do you do if your fish is not eating?

If your fish are not eating, there are a few things you can do. First, try to vary their diet. Sometimes if you are feeding the same foods every day, the fish will start to shy away from it.

They get bored with the same foods all the time. That doesn’t mean you need to stop feeding that food altogether, but you can offer it on different days with another type of food.

You might try a different brand of food or a new type. Switch from flake, pellet, frozen, and live foods to keep their diet varied. 

Also, make sure that you are using good quality food from a known brand. This is important as the ingredients are specific for the types of fish you are feeding.

There are some highly trusted brands like NLS, Rod’s food, and Easy Masstick. 


easy masstick fish food


Check your water parameters to ensure everything is within limits. You may need to perform a water change and adjust your maintenance schedule to ensure your tank demands are met.

If you have a sick fish that is not eating, consider removing the fish and place it into quarantine to be treated. 

If a fish is being bullied or outcompeted for food, consider removing it as chances are it will struggle to get proper nutrition. 


Check out: Best food for clownfish (They love this stuff)

How do I get my saltwater fish to eat? Tips for fussy eaters

It’s common for certain fish to be fussy and not eat for a period of time. This is normal for new fish being added into the tank. It might take them a while to become comfortable and start eating. Sometimes they will eat right away.

If you have a wild-caught fish, they are not familiar with commercial-grade foods and will only eat live. It’s all they know. For fish that have been in your tank for a while and are just being fussy, try to change up the foods and mix in a variety of flakes, pellets, and frozen.

Normally once you offer a mix of different foods they will become more interested.  You can also change your feeding schedule to different times throughout the day.

If you have been feeding on the same schedule for a long time and suddenly notice the fish are not eating as much, try switching things up. It might make a difference. 

How long can my saltwater fish go without food?

To keep your saltwater fish healthy for the long term, it’s important to feed them a proper diet and offer a few small meals throughout the day.

Not feeding your fish for a long period of time is a bad idea. Fish are known to live without food for quite a while, but starving them is simply the wrong thing to do. 

Fish can generally go 3 days without food. Some can go much longer. Larger more mature fish can go longer than juveniles. Up to a week is possible but it’s not something to intentionally do.

If you are away from your tank for a few days without feedings, it shouldn’t be an issue.


As you can see, there are many reasons why your fish may not be eating. The most common reason is poor water quality and this can be addressed by performing water changes and increased husbandry. If your water quality is good, check for signs of illness or stress.

Providing good quality foods that are specific for the types of fish that you keep is crucial for keeping them on the proper diet which will keep them healthy and eating every day.