Why is my fish constipated?


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We’re all familiar with the sight of a fish trailing its faeces. We look at some of the common causes of constipation in fish, and what you can do to treat it.

Intestinal parasites primarily affect African cichlids and South American detritus eaters like Discus.

Look for white or pale faeces — this is the mucosal lining of the intestine being shed in an effort to expel the pathogens. Worms may be visible from the anus or in droppings.

The protozoan parasite Hexamita can cause muscular wasting and constipation at the same time.

Pending diagnosis, medications like eSHa’s NDX or Octozin by Waterlife will help if used early on. Your local store will be able to advise the correct medication from particular symptoms, and taking some fish faeces to look at under a microscope might be a great help for them.

Poor water quality

Fish in poor water quality have reduced appetites, refusing to eat when ammonia or nitrite rises. They then start to defecate their mucosal gut lining, leading to a milky, transparent poop… and a constipation misdiagnosis!

With improved water quality, appetites and digestive transit will return back to normal.

Temperature changes

Temperature changes can cause bloating or blockages. The metabolisms of temperate fish are temperature driven, and as things cool their gut flora becomes less efficient, causing slow digestion.

Monitor weather forecasts (especially in springtime) and don’t overfeed pond fish during one of the brief, warm ‘fool’s springs’ that occur.

Internal tumours

Internal tumours may press against the stomach or intestine, making it difficult to pass food through.

Physical deformities

Physical deformities, such as those in Balloon fish or fancy goldfish, cause organs to be displaced or press against each other.

It is often down to the fish’s own vitality whether it pulls through or not. Ensuring the highest quality and appropriate diet will go a long way towards helping.

Physical blockages

Physical blockages occur in ‘grubbing’ fish like goldfish, which have evolved to take in mouthfuls of sand, silt and mud. When placed into a tank with pea gravel, it may be swallowed, blocking the oesophagus.

Physical blockages will require a vet, as it is likely you’ll damage the fish trying to remove any obstruction. Avoid this by using either very fine substrates, or substrates larger than fish can ingest.

Incorrect diet

Incorrect diet is a major player. While many fish are extremely versatile in their eating habits, some foods simply do not suit some fi sh.

The digestive systems of fish come in a couple of variants. Carnivorous or piscivorous (fish eating) species have evolved to possess a large stomach in which big, protein-rich diets (such as whole fish) can be digested, and a short intestine.

Herbivorous fish tend to have a small stomach, but as plant matter is notoriously hard to extract nutrients from, they have a long intestine, allowing the food to stay in the body for a long time until all the goodness is pulled from it.

Feeding a carnivorous fish on plant matter usually just results in a fi sh that rapidly emaciates and dies. Feeding a herbivore on a high protein meaty diet exposes them to ingredients that they simply don’t have the enzymes to digest, and such foods will be dangerously slow to pass through their long intestines.

It really is as simple as changing diet to suit the fish in this instance.

Surface feeding

Surface feeding plays a role, especially in goldfish. Goldfish are phyostomous, with a duct between the swim bladder and the oesophagus, for the purpose of getting air into the swim bladder.

When goldfish feed on floating flakes or pellets, they are prone to swallowing down gulps of air with them. Once inside them, it not only interferes with digestion but also causes buoyancy issues.

Pre-soaking flake foods for a few seconds, or using sinking pellets is the best way to avoid air gulping. The fish might not understand at first and still instinctively gulp at the surface, but they’ll work it out.

Stale or spoiled dry food

Stale or spoiled dry food is way more common an issue that you might think, too. Lots of fishkeepers seem to think that dry fish food will retain its nutrients indefinitely, whereas the reality is that many foods will lose a considerable chunk of their vitamins around six months after opening.

Feeding two-year old flake to a goldfish is like feeding yourself on paper — nutritionally void. Inadequate nutrients mean poor digestion, and poor digestion leads to low quality faeces — trailing poop!

When you open a tub of food, use a marker to note the date of opening on the bottom of it. After six months, discard and replace for fresh. When feeding, always use dry fingers, as moisture in the tub will promote mold and ruin nutritional value.

Lack of fibre

Lack of fibre is something that can cause constipation, but not with any particular regularity, and almost always only in tandem with offering improper diet or stale foods. Still, it can happen, especially if using a cheap food with exceptionally low fibre content.

A great source of roughage is in the shells of Daphnia. Offer them live or frozen instead of dried foods a couple of times a week, and the hard shells will help to keep guts clear.

Are shelled peas a cure for a constipated fish?

You’ll often hear of shelled peas as a cure for constipation. While they do have some effect, it is mainly because they are low protein and reduce underlying water quality issues, rather than being some kind of superfood. 100g of peas contains about 5g protein, while 100g of flake or protein could have between 30 and 50g protein. Protein = ammonia = water quality issues.

  • Peas also contain high vitamin levels (including vitamin C) which may be lacking from stale dry foods — simply adding fresh foods to begin with would avoid the issue.
  • Peas sink when fed, meaning that Goldfish won’t gasp at the surface, so air won’t get trapped in their bellies.
  • Lastly, it’s claimed that peas have a high fibre content. While peas contain around 5% fibre, so too do many dry foods.
  • Still, some fish LOVE peas, so don’t be afraid of offering them from time to time!

How can I tell if my fish is constipated?

  • Long dark faeces hanging from the anus.
  • Long white faeces, or a milky transparent ‘tube’ hanging from the anus.
  • Bloating and distension, specifically around the stomach area. If the entire fish is swollen, with scales sticking out like a pinecone or bulging eyes, then this is dropsy, and not a constipation issue.
  • Refusal to eat and plump looking fi sh.
  • Balance issues, especially a fish floating ‘belly up’ or struggling to right itself.