Fish do get constipated! It is a problem especially for laterally compressed fish and some fish species seem more prone to it, such as Goldfish and Bettas. It can also be caused by an improper diet, some manufactured fish foods, or overfeeding. Constipation can and will kill your fish if the blockage is not addressed.
As it is with humans, roughage/fiber is important to avoiding fish constipation. Even carnivores get vegetation through the stomachs of the fish they consume in the wild, and roughage from bones and crustaceans. Make sure that your fish receives the appropriate amount of fiber/roughage in a form that is suitable for their dietary requirements. The amount required for good digestion depends on the fish, so some research is in order. Too much for the wrong fish or via the wrong source is also not good for their digestive system.
Carnivorous fish, as a general rule, do not digest vegetable fiber well and it is not required in high quantities due to a short digestive tract. According to About.com’s Freshwater Fish Expert, Shirley Sharpe, a carnivore diet should contain less than 4% fiber. Not all fish ‘classed’ as Carnivores are created equal though, so research your particular fish. For example, many fish species classed as carnivores will also snack on algae or seaweed in the wild. This fact extends to terrestrial species in the order carnivora as well. The carnivora order contains more than 260 species, most of which are actually omnivores.
That being said, it should also be noted that seaweed and algae differ from terrestrial plants. They are low in carbohydrates and don’t present the various binding and anti-nutrient issues of terrestrial plants. This makes seaweed and algae a far more suitable form of dietary vegetation, even for obligate carnivores.
Herbivorous and Omnivorous fish require far more vegetation in their diet than Carnivores, some more so than others. It’s never a simple matter of half and half for omnivores. Most Mollies, for example, are omnivores that require a higher intake of vegetation than your average omnivorous tropical fish.
High protein diets without adequate vegetable fiber are going to be very difficult for a herbivorous (and many omnivorous) fish to process. Your veggie-loving fish have long digestive tracts and a diet with adequate fiber is required for efficient and optimum function. ‘Optimum’ being the operative word – some fish will appear to do just fine without any special dietary efforts, but that does not mean that their digestive system isn’t struggling to handle it, which can be an invisible source of stress.
For herbivorous and omnivorous fish, offset high meat protein meals with nutrient-dense high-fiber, low-medium carbohydrate meals. Avoid or limit high carbohydrate foods such as corn, sweet potato, parsnips and bananas. Make sure your vegetable fish food is primarily vegetation (a label of ‘vegetable’ or ‘spirulina’ does not always mean that the product contains a high percentage of said vegetation).
Vegetable protein is an awesome form of protein for your herbivorous and omnivorous creatures, such as the protein in seaweed and peas. Vegetable protein offers efficient uptake & digestibility, with the uptake from seaweed and algae being far superior by comparison to any terrestrial plant.
Some high protein foods are notorious for causing constipation, especially Bloodworms. Be it the shape or the high protein & iron they contain, Bloodworms are best avoided for fish prone to constipation. They should be fed sparingly as a treat if you feed them at all, in my opinion.
Dr. Jim Greenwood of the Canterbury Veterinary Clinic suggests we avoid large imported bloodworms entirely, “A note of caution here on feeding the larger imported frozen bloodworm. These worms have a chitinous exoskeleton and numerous bristles that are indigestible for fishes with small intestinal apertures. The meaty portion of the worm is readily processed, but the hard bits remain and clog up the stomach in an immovable mass. Be careful not to feed your discus, rainbows and some tetras on the larger bloodworms.”
When you combine high protein with roughage, however, you can cover all of your digestive bases, leaving only the nutritional balance to concern yourself with. Krill, shrimp and daphnia provide roughage with the protein.
You may wish to presoak foods to avoid constipation, especially super-hard pellet forms. There’s a happy medium there – soaking them too long may cause the food to lose its nutrient value. If you soak the food and it’s still hard & largely the same size after a reasonable amount of time, switch to another brand. Often in the desire to be stable in water, foods are difficult to consume and digest no matter how digestible the label claims the ingredients are. Likewise, if the food expands too much, feed very little as the fish will overeat and repent later. Freeze-dried or other whole dry foods should be briefly presoaked for fish who are particularly prone to constipation, especially surface feeders.
Internal parasites may also cause blockages, but that is another problem entirely. You can use preventative measures here too, however, by quarantining new fish and feeding foods with natural anti-parasite properties. The easiest way to accomplish the latter is to make your own fish food that includes anti-parasite ingredients, such as seaweed, calcium montmorillonite clay, and crushed garlic. Note that the active component in garlic is allicin, which is heat sensitive. Since manufactured fish food is processed at high temperatures, the garlic in them does little good in this regard.
Toxic chemicals and fillers in some manufactured pet food are also suspected culprits of digestive issues in animals. We highly recommend limiting manufactured fish flakes and pellets in the diet of any fish and invertebrates, especially those with digestive issues. Alternatives include fresh, frozen, freeze-dried, low-processed or a homemade formulation. Try to find a fish food brand that doesn’t use synthetic anti-oxidants (such as toxic ethoxyquin) or artificial coloring.
You may observe small or non-existent bowl movements, or hard, trailing feces. Passing undigested pellets are another indication that all is not well with your fish, be it a problem with digesting them or overfeeding. The fish may also bloat, which is often the first symptom a hobbyist notices. This may also cause erratic, uncontrolled swimming.
Unfortunately, the bloat that constipation causes will often be mistaken for a disease, such as ‘Dropsy’ (which is more a symptom of a disease than a disease itself). It can also include swim bladder symptoms as the blockages and swelling can impact the swim bladder, making the fish swim erratically. Hobbyists will often medicate for ‘Dropsy’ or ‘Swim Bladder Disease’, only to have problem worsen. The first step in any situation where a fish is bloated from an unknown cause should be to treat for constipation, unless there are other symptoms of disease.
Luckily you have two choices of treatment for constipation in fish, but the first steps are the same.
- Stop feeding (except for foods suggested below)
- Do an aquarium water change.
- Turn the aquarium heater up a degree or two.
Then use one or both of the following methods to remove the blockage:
Food Method: If the fish will eat, try feeding softened (barely cooked), pealed, quartered peas, or presoaked freeze-dried or fresh Daphnia. Chickweed may also be effective if you can get the fish to eat it.
Epsom Salts: If the fish won’t eat, treat the water with pharmaceutical-grade, organic Epsom Salts. You can also combine the two treatments if the fish seems to be worsening too quickly to wait for an outcome.
Some say you can just add the Epsom Salts to the tank and do a water change when the fish has a bowel movement. Others say it should be given in a bath. If the fish is in a quarantine tank I would leave it in the salts until they work, but not for more than 24 hours. The reason I say that is because I believe that moving the fish in and out of a bath is more stressful. You can also reduce the amount of Epsom Salts for a long term bath. If you don’t like that idea, place the fish in an Epsom Salt bath for about half an hour and then return him to his aquarium or quarantine tank. The standard recommended dosage for Epsom Salts is 1 tsp/gallon, but recommendations can vary too.
Once the blockage has been removed, resume feeding your fish in small amounts. Select easily digested (preferably whole) foods. You may wish to reevaluate the diet and make changes based on the natural feeding habits of your fish in the wild.
You should also provide a clean, calm environment to avoid stress-induced secondary infections.
When It Doesn’t Work
If the treatment for constipation does not work on your bloated fish, you are probably looking at one of two things:
- An internal injury or
- A bacterial infection
Unfortunately, successful treatment of either condition is rare. I have never had luck with antibiotics but you may want to try them. If so, be sure to treat in a quarantine tank and follow the directions on the package to the letter. Also be aware that many antibiotics will inadvertently kill beneficial bacteria in the aquarium, resulting in a new aquarium cycle.
If the fish does not seem to respond, you may consider humane euthanization. Hopefully it will not come to that and the odds are for you – the majority of bloat cases are, in fact, digestion related.
James Sales, Geert P.J. Janssens. Nutrient requirements of ornamental fish. Aquat. Living Resour. 16 (2003). Faculty of Veterinary Medicine, Belgium.
Carl D. Webster. Chhorn Lim. Nutrient Requirements and Feeding of Finfish in Aquaculture. Aquaculture Research Center, Kentucky State University, Frankfort, KY 2002.
Halver, J.E., Hardy, R.W. Fish Nutrition. Second ed. Academic Press, San Diego, CA, USA. 1989.
Winfree, Robert A. Nutrition and Feeding of Tropical Fish. Aquariology Fish Anatomy, Physiology, and Nutrition. First ed. Tetrapress, Morris Plains, NJ 1992.
Dreyer, Stephan. Feeding Tropical Fishes the Right way. TFH Publications. 1998.
Robert, Helen E. Fundamentals of Ornamental Fish Health. 2009.
✔ You may also be interested in reading
Natural Prevention and Treatment of Aquarium Fish Parasites
Natural Fish Food for Fancy Fins
Live Fish Food Cultures for the Home Aquarium
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