When is fasting sick fish necessary? Quick Answer: Never

Many “internet fish helpers” recommend fasting sick fish, or decreasing their diet, and we have to ask…WHY?!?!?

Dangers of Fasting Sick Fish

If you were constantly swimming to survive, you’d be burning a lot more calories than sitting at your desk, reading this article. When you’re sick, you often want to lay around in bed because your body is working so hard to get you back to normal. All of your energy has been diverted to keeping you alive. A sick fish, who is still swimming, won’t appreciate the lack of food. When they stop swimming and get stuck on the bottom or top of their tank, the additional stress could make other maters WORSE. Fasting sick fish is going to be counterproductive and likely only make them sicker.

Most of the reasoning behind dropping your fish’s calories is to prevent excess ammonia in your tank. This is a lazy excuse for not doing your water changes, not having enough filtration, having too many fish or not starting your tank properly. Don’t punish your fish for your laziness, overstocking or lack of preparation.

Many negative buoyancy disorders we see in fish are actually sick and don’t have the energy to swim or eat. If you stop feeding them, you can make their health issues even worse.

Fasting Sick Fish for Constipation and Peas

Oohhh boy… This is one of those fish myths that we just can’t seem to get rid of. The internet is full of fasting sick fish with “constipation,” and then feeding them a pea or two. How this fixes your sick fish? We’re not too sure.

Problem #1: Your fish is not constipated. This just isn’t physiologically possible in fish living in an aquatic environment.

Problem #2: You are withholding food which is not a treatment for constipation. If your kid or dog is constipated, do you just stop feeding them? No, so don’t do the same to your fish.

Problem #3: All that “fiber” in peas isn’t helping your fish. Peas are pushed on fish for their fiber content which they don’t really have that much of (5.7%) and your fish cannot digest much of since they lack an acidic stomach.

Mostly, this decreases your fish’s protein intake, decreasing their ammonia intake, which likely will fix their water chemistry issue temporarily (see above) or that pea is the first decent food they have seen in a long time since they have been eating ancient pellets or even worse, flakes.

Here are the rare instances fasting sick fish or a decreased diet is necessary:

Your fish does not WANT to eat and ignores the food you offer.

Decreased appetite in fish can be a sign of illness and should be carefully considered. If your fish is not interested in food, double check your thermometer to ensure their tank is within their optimal range. And please use a legitimate thermometer, not a sticker. If your fish’s temperature is not within the correct range, take steps to correct this by either adding a heater or cooling fan.

Keep in mind that if you have recently done a water change, especially a larger percentage one, this may have temporarily changed your water temperature. Whenever possible, adjust your fresh water to within 5 degrees F of the current tank or pond temperature. We understand this may not always be possible, but just know that large temperature swings could stress out your fish and cause them to not be interested in eating.

Your fish is about to undergo surgery by a qualified fish veterinarian.

Just like fasting your other pets or yourself before surgery, fish should not be fed the morning of surgery. That being said, if you do forget and your fish is not fasted prior to surgery, they will probably be okay. This comes down to very different anatomy in fish and those animals with lungs. For those animals with lungs, we are mainly concerned about aspiration of stomach contents getting into the lungs if the patient has recently eaten. For fish, if they aspirate, it may slightly cloud the gills, but can be easily flushed away.

Your betta has been overfed and cannot digest any more food.

We see severe indigestion in betta fish that are overfed in too cold water. This causes their digestion to get backed up and they start to resemble a marble with long fins. If this happens, there is not much we can do for them to correct this. Their intestines are very simple and cannot digest large volumes of food. Contact your fish veterinarian ASAP to discuss possible remedies for your fat betta.

Your fish veterinarian may or may not recommend withholding food. Bettas require a ton of energy to swim and keep their massive fins off the bottom. Typically, they will recommend a diet decrease, not pure fasting.

The water in your outdoor pond is too cold or too warm and your fish aren’t interested in eating.

Similar to the above point, but if the water is outside of your fishes’ preferred temperature range, their minds just are not concerned with eating. Best sure to check your outdoor pond water temperature, not air temperature, to see if they are within range. Not all ponds will be exactly the same in appetite at various temperatures. For our guidelines, please view this reference.

If the pond is between 60-80F (15-27C), your fish should be interested in eating something. If they are not, this can indicate there is a serious disease and your fish will require assistance. Do not wait more than a day or two for them to start acting normal. The faster you get help, the better chance your fish will survive.

When your fish is sick, please do the following:

Rather than fasting sick fish, here are some alternative steps to take in order to keep them healthy.

1. Test your water quality. This is the #1 cause of disease in fish. If your water is not within the correct range, take immediate steps to fix this. It may take a day or two for your fish to resume eating once water quality issues have been fixed.
2. If you cannot maintain your fish tank or pond yourself, you may want to hire a professional. In all honesty, if you can’t maintain your tank or pond, why do you even have one?
3. Check your fishes’ food. If it is moldy/off-color/smells bad (something other than “fishy”), TOSS IT. Any fish food older than 6 months needs to be replaced. The expiration date on the packaging is only if it remains on the pet store shelves. Once it has been opened, please store it properly in an indoor, sealed container to ensure best shelf life.
4. If fixing the water chemistry and feeding a good diet has not improved the issue, CALL YOUR VETERINARIAN. Yes, fish veterinarians exist. If you go for the “free” help online, remember, you get what you pay for. The sooner you get help for your fish, the faster they will get healthy.

We see a lot of silly fish stuff on the internet. Do your part and do not perpetuate these myths.

If you like more fish myths, check these out.

Other Articles You Might Like

• When Do You Need a Fish Vet?
• Preventative Medicine in Fish
• Stress in Fish