Description of "bloat" in cichlid fish
by Jason Selong ( Big Sky Cichlids )

Indications. The term "bloat" or "Malawi bloat" generally renders images of cichlids swollen to near apparent bursting and breathing at a rapid rate.  A fish observed in this condition usually succumbs in a short period of time. 

Bloat has been related to internal parasitic infections, bacterial infections, feed, and water quality.  These observations suggest that bloat itself is not a disease, but rather a symptom of a variety of disease and water quality related problems, each with their own possible remedy.  The observation that bloated fish often succumb quickly suggests that these problems must be addressed prior to the fish reaching that condition.


The physiology of freshwater fish offers insight into the possible mechanism for bloat in cichlid fish.  The tissue of freshwater fish is hypertonic compared to the surrounding water.  This results from internal tissues having a higher ion concentration than the water around the fish.  This creates osmotic pressure and causes freshwater fish to gain water by diffusion.  Freshwater fishes combat osmotic pressure by producing dilute urine and actively transport mineral ions from the surrounding water to compensate for those lost via the urine and diffusion from the gills.  (Note: marine fish have the reverse problem where tissues are hypotonic compared to surrounding water and they must ingest large volumes of water and actively excrete mineral ions).  This water balance mechanism is called osmoregulation.  The ability to osmoregulate is essential to the well-being of fish and allows fish to tolerate a range of water quality conditions by maintaining a constant (homeostatic) internal environment.  A general breakdown in osmoregulation due to disease, water quality, etc.., may be responsible for the bloated condition that results from excess water accumulation in tissues.  It intuitively follows that fish in this condition often rapidly succumb due to loss of homeostasis (the constant internal environment), essential to carrying out metabolism and other life activities.  

Tropheus spp. and Malawi mbuna are considered high risk for developing bloat

Treatment. Diagnosing the underlying cause responsible for bloat is critical in determining the proper treatment.  Disease, in many cases, has been identified as a leading cause of bloat.  Parasitic organisms generally multiply rapidly and will attack more than one fish in a closed system.  Preventing parasitic infections requires quarantine and observation of any new specimens and perhaps prophylactic treatment.  Be forewarned compounds found effective in treating parasites (e.g. formalin, copper compounds) are toxic to all aquatic life and work by killing parasites at lower concentrations than those that would harm the host fish.  Wild caught fish are more likely to carry parasites and should be quarantined and observed for external as well as evidence of internal parasitic infections.  Bloat in cichlids has been related to a gastrointestinal infection by parasites (Hexamita spp. and Cyrptobia iubilans) and bacteria (Aeromonas hydrophilia) (Francis-Floyd 99).  Bacterial infections in otherwise healthy cichlid aquariums are probably more rare.  Bacteria (both opportunistic and obligate pathogenic) must first defeat the fish's immune system in order to survive and multiply.  Fish stressed due to other causes (parasitic infection, water quality, aggression) are more likely to contract bacterial infections.  A variety of antibiotics are indicated to treat specific types of bacteria.  Separation of the affected fish is probably indicated to prevent non-infected fish from contracting the disease.  Water quality should be closely monitored since antibiotics may disrupt nitrifying bacteria.  Any equipment associated with the aquarium (e.g. nets, decorations) should also be disinfected prior to use to prevent contamination.  Poor water quality should not be overlooked as an underlying cause for bloat or disease.  Water quality can rapidly deteriorate in closed systems, particularly at the high densities and feeding rates commonly observed in cichlid aquariums.  Poor water quality increases stress on fish and allows opportunistic infection to occur.  Prevention of degraded water quality is the easiest and least expensive treatment, and a regular -I would recommend weekly- schedule of water changes should be strictly adhered to.  Many feed related issues suggested to result in bloat may possibly be explained by poor water quality and a buildup of metabolites.  Again, strict adherence in maintaining optimal water quality will prevent many problems.  Aggression may be another cause of bloat in an otherwise healthy cichlid aquarium.  Repeated aggressive attacks on a particular fish may cause such damage that the ability to osmoregulate is lost, resulting in bloat.  I have observed this in a group of P. demasoni where a sub-dominate male was repeatedly attacked and subsequently developed bloat and was unable to be saved.  In summary, bloat in cichlids may result from  diminished capacity to osmoregulate and be symptomatic of a variety of factors rather than a single condition.  This makes diagnosing the underlying cause essential in determining the correct choice for treatment.

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