5 Reasons for an Inactive Rainbow Shark (And What To Do)


Okay, let’s clear up the air. Some claim Rainbow Sharks are aggressive, active, and practically can’t stay still. Others claim they’re shy and like to hide.

Should Rainbow Sharks Be Active?

Rainbow Sharks are more docile when they’re young. But mature Sharks are active and strong swimmers. That’s why they need a wide, lidded aquarium as they tend to jump out.

However, they also spend a lot of time hiding in caves or tunnels and they are very territorial of these. They will actively chase other fish out of their territory when needed.

A juvenile Rainbow Shark is more timid and won’t likely cause problems even if it’s in a tank with fellow Sharks. That’s why you can see a big group of them together in the pet store.

But once they reach a length of 2 inches or more, they start to assert their dominance in the aquarium.

Thus, a Rainbow Shark has both very active and very solitary moments.

Why Would a Rainbow Shark Stay Inactive?

Before we consider the worst, let’s eliminate all other possibilities that have to do with the Rainbow Shark’s personality. Aside from what we mentioned above about the Shark being a juvenile, here are some more possible explanations why the fish might seem inactive.

Reasons for Inactive Rainbow Shark
5 Reasons for Inactive Rainbow Shark

Reason #1: It likes to hide especially during the first few weeks in a new aquarium.

A newly-introduced Rainbow Shark to an already established tank will trigger its shyness especially if there’s an existing tank alpha or ‘boss’ already.

While some Sharks become more visible after it’s adjusted to a new tank, some just want to stay and hide. They can choose not just caves, but pots, roots, plants, and even buried under the substrate as well. It may not even come out to eat in the first few days in your aquarium.

Some Sharks also like to ‘lay down’ as if it’s resting. As long as it looks healthy, this is normal (and funny and adorable) behavior. Some even say they’re playing dead.

When it’s out of sight, it may give off the impression that it’s inactive. This brings us to the next reason.

Reason #2: It’s active but you don’t see it

We’ve answered the question of whether fish sleep on our post here. Fish have moments of inactivity and in the case of the Rainbow Shark, it might be during the day.

There are Rainbow Sharks that choose to leave their tunnels or caves when the rest of the fish are asleep and not a threat to their territory. These nocturnal fish eat and roam around the tank at night instead because it’s more comfortable doing so.

Rainbow Sharks also love to dig. As we mentioned here in one of our posts, there are even Sharks who disappear for weeks at a time, thought to be dead, only to be discovered later hiding underneath the substrate.

You shouldn’t be overly concerned as long as the Shark looks healthy.

Reason #3: Tank water issues

But sometimes the problem is just starting. For example, the accumulating presence of ammonia or nitrites will affect the behavior of the Rainbow Shark.

If it just recently became inactive, check your water chemistry. Try to detect toxins ASAP and do a partial water change if you find levels above 0 ppm. Nitrates are acceptable up to 40 ppm (20 ppm being the usual).

Look for temperature rise as well. Higher temperatures lessen the amount of oxygen in the tank and would cause your Rainbow Shark to either go crazy (like trying to jump out) or stay in its place.

However, it’s not good if the temperature is constantly swinging as this will stress not only your Shark but all the fish in your tank as well. Keep it consistent at around 77 to 78 deg F and you’ll be fine.

All fish starting to act strange would indicate poor water conditions. Some might be near the surface gasping for air or others might show reddened gills as a result of ammonia burn. If this happens, do a 50% water change ASAP.

If the ammonia level reaches 2 ppm, transfer the fish to a temporary aquarium while you cycle the water in the main tank. You may get some tips from our post here on how to get cycled water without waiting weeks.

If all the other fish seem fine and it’s just the Shark that seems inactive, it may have other issues.

Reason #4: Inability to feed

If your Rainbow Shark is lethargic and dropping weight, it might not be eating well. Although this is a rare occurrence (as Sharks can live off on practically anything), there are situations when the other fish are simply faster in getting to the food.

This is a concern and you have to support its nutrition ASAP.

Sharks are omnivorous bottom feeders and would benefit from sinking food and pieces of vegetables. For tips on how to feed your Rainbow Shark better, refer to this page. We discuss methods and tricks on how to get your Shark eating and what types of foods are best for its health.

If the problem is another Shark, then make sure you have at least a 125-gallon to accommodate them both. Rainbow Sharks should not be kept with other similar-looking fish or they will attack one another, causing the less dominant ones to constantly hide and cower. We strongly suggest you only ever keep one.

Reason #5: Disease

You also have to spot signs and symptoms of possible diseases. If your Shark is swimming oddly, is tired from trying to swim upright, or losing its color, it may be swim bladder disorder or internal parasites.

These may have been caused by the water in the pet store where you got the Shark from (if you recently acquired your Rainbow Shark) or stress.

Swim bladder problems are more obvious for Sharks that struggle to keep upright and have difficulty swimming. Mild cases that are caused by constipation can be treated with Epsom salt baths which we discuss in our post here, but swim bladder infections caused by bacteria will need antibiotics like Maracyn.

Internal parasites are probably if your Shark has not been eating and has white stringy poop. While it’s difficult to find out how the parasite entered your aquarium, it will be best to isolate your Shark and all infected fish in a hospital tank so you can medicate them there.

The disease can be cured by methylene blue soaks or aquarium salt baths or API General Cure. Make sure to follow instructions carefully. Also, make sure that your fish are eating to increase their immune health as this will help them fight off the disease.

If the Shark’s condition is mild and you want to use salt as your method of treatment, you may want to get some more information about that from our post here.

For the onset of most other forms of parasites, the Shark would become irritable and not inactive.

Final Thoughts

The Rainbow Shark has a very interesting personality ranging from being very active to having bouts of inactivity. In all these, its health and appearance will always tell you whether there’s something wrong or not.

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