10. Diseases

Diseases are generally not a problem in aquariums which have over-filtered, crystal clear, bacteria-free water.

The Key to Good Fish Health is Clean, Clear, Bacteria Free Water

Note this does not mean water which is changed frequently.  The idea that water changes create good health is a myth. The idea that water which has “good water parameters” will give good health is also a myth.

We go into this in much greater detail in this article:

12.9. Avoiding Fish Diseases (links to aquariumscience.org)

Krobia xinguensis
Krobia xinguensis

Bacteria in the Water Column

The fish’s immune system is constantly fighting all the bacteria that the gills are exposed to regardless of the type of bacteria. So a lower bacterial count means more immune system resources available for fighting off pathogens. A high bacteria concentration will compromise the immune systems of the fish and can cause any number of diseases and pathogen breakouts. The easiest way to determine the amount of bacteria in the water is by water clarity. In general, the clearer the water, the fewer bacteria. All owners of aquariums should strive for crystal-clear water.

Note that “bacteria-free” is relative. It is all on a logarithmic scale. A milliliter (or cubic centimeter) of dull, “normal” aquarium water will have roughly ten million or 107 bacteria. A milliliter of cloudy water can easily have ten billion or 1010 bacteria. And a milliliter of “crystal clear” water can have as little as 100,000, or 105 bacteria in it. This means that cloudy water has 100,000 times more bacteria in it than does crystal clear water. This gives one an idea as to why reducing the bacterial count can be so effective in improving the immune systems of the fish.

Pseudotropheus sp. kingsizei
Pseudotropheus sp. kingsizei

If the bacteria count in the water column is low the fish can put all their immune system resource towards keeping pathogens at bay. So fish in bacteria-free water is far more healthy than fish in bacteria-laden water. This is simply the best disease preventative there is.

Note that, contrary to popular myth, this does NOT mean water which is changed frequently. This is because of the logarithmic nature of bacteria numbers. Going from a billion bacteria to half a billion bacteria with a 50% water change isn’t going to be that much help to the fish. Using over-filtration to go from a billion to a million bacteria will help a lot. Large water changes cannot compensate for poor filtration.

Further analysis of this bacteria can be found at this link:

4.3. Bacteria in the Water Column (links to aquariumscience.org)

Rocio octofasciata Jack Dempsey electric blue
Rocio octofasciata, Jack Dempsey, electric blue

Myths About Diseases

There are many myths parroted on social media about diseases. Here are just a few of them:

  • Testing water parameters is essential to diagnosing fish diseases.
  • Fish absorb medicines through their skin and gills.
  • Freshwater fish drink the water they swim in so putting medicine into the water gets the medicine into the fish.
  • The use of “chemicals” such as copper, metronidazole, praziquantel, and antibiotics to treat fish diseases should be avoided as they will probably kill the fish.
  • Salt (sodium chloride) added to the aquarium assists in the healing of injuries, promotes the formation of slime coating, improves gill function, and kills some parasites.
  • Using antibiotics in the home aquarium will result in antibiotic-resistant bacteria.
  • Frequent water changes help cure fish diseases.
  • Ich is a horrible disease that will kill most of the fish infected with it.
  • “White-eyes” is due to water quality issues.
  • If fish get red blotches on their skin and fins in an aquarium it is generally something called “ammonia burn”, not bacterial hemorrhagic septicemia.
  • Herbal, “organic” and “natural” remedies (Melafix, Pimafix, Garlic) are effective treatments for fish that are diseased.

These myths are ALL false.    

Herichthys Carpintis, Green Texas Cichlid
Herichthys Carpintis, Green Texas Cichlid

Diagnosing Fish Diseases is VERY Difficult

One caution about diagnosing fish diseases. Even with a microscopic examination fish diseases are not easy to diagnose. Most hobbyists have only what their eyes tell them to go on as to what any fish disease is. This means that diagnosis of any fish disease is simply a “best guess”. And these “best guesses” are frequently wrong. So keep this in mind in all the following disease articles.

If one has a disease break out, these chapters can hopefully help:

10.1. Diseases in General (links to aquariumscience.org)

10.2. External Protozoans (links to aquariumscience.org)

10.2.2. Ich (links to aquariumscience.org)

10.2.3. Velvet (links to aquariumscience.org)

10.2.4. Epistylis (links to aquariumscience.org)

10.2.5. Chilodonella and Costia (links to aquariumscience.org)

10.2.6. Tetrahymena (links to aquariumscience.org)

10.2.7. Cryptobia (links to aquariumscience.org)

Tropheops Red Fin Puulu
Tropheops Red Fin Puulu

10.3. Bacterial Diseases (links to aquariumscience.org)

10.3.1. Skin Ulcers (links to aquariumscience.org)

10.3.2. Mouth Rot (links to aquariumscience.org)

10.3.3. Duck Lips (links to aquariumscience.org)

10.3.4. Fin Rot (links to aquariumscience.org)

10.3.5. Saddleback (links to aquariumscience.org)

10.3.6. Red Blotches (links to aquariumscience.org)

10.3.7. White Eyes (links to aquariumscience.org)

10.3.8. Pop Eyes (links to aquariumscience.org)

10.3.9. Red Gills (links to aquariumscience.org)

10.3.10. Red Mouth in Goldfish (links to aquariumscience.org)

Synodontis multipunctatus
Synodontis multipunctatus

10.4. Tuberculosis (Fish TB) (links to aquariumscience.org)

10.5. Hexamita (links to aquariumscience.org)

10.6. Flukes (links to aquariumscience.org)

10.7. Fish Saprolegnia or “Fungus” (links to aquariumscience.org)

10.8. Lymphocystis (links to aquariumscience.org)

10.9. Anchor Worms (links to aquariumscience.org)

10.10. Black Spot (links to aquariumscience.org)

10.11. Tapeworms (links to aquariumscience.org)

10.12. Nematodes (links to aquariumscience.org)

10.12.1. Camallanus (links to aquariumscience.org)

10.12.2. Capillaria (links to aquariumscience.org)

10.13. Pests in the Aquarium (links to aquariumscience.org)

10.14. Fish Lice (links to aquariumscience.org)

10.15. Dwarf Gourami Disease (links to aquariumscience.org)

10.16. Graphite Disease in Bettas (links to aquariumscience.org)

Selenotoca multifasciatus Silver Scat
Selenotoca multifasciatus Silver Scat

Some general articles will be useful when treating any fish disease:

12.1. Basics of Treatment (links to aquariumscience.org)

12.2. Various Treatments Summarized (links to aquariumscience.org)

12.3. Quarantine Tanks (links to aquariumscience.org)

12.4. Ineffective Medications (links to aquariumscience.org)

12.5. Fish Don’t Drink (links to aquariumscience.org)

12.6. Sterilization (links to aquariumscience.org)

12.7. Making Medicated Food (links to aquariumscience.org)

12.8. Euthanizing a Fish (links to aquariumscience.org)

12.9. Avoiding Fish Diseases (links to aquariumscience.org)

12.10. The “Shotgun” Approach (links to aquariumscience.org)

Sciaenochromis fryeri OB Blueberry
Sciaenochromis fryeri OB Blueberry

This is in addition to a chapter on symptoms. These articles are as follows:

11.1. Hole-in-the-head Syndrome (links to aquariumscience.org)

11.2. Stringy White Poop (links to aquariumscience.org)

11.3. Malawi Bloat (links to aquariumscience.org)

11.4. Dropsy (links to aquariumscience.org)

11.5. Hollow Belly (links to aquariumscience.org)

11.6. Swim Bladder Disease (links to aquariumscience.org)

Rineloricaria parva Whiptail Catfish
Rineloricaria parva Whiptail Catfish

11.7. Shimmying (links to aquariumscience.org)

11.8. Twirling (links to aquariumscience.org)

11.9. Spinal Deformities (links to aquariumscience.org)

11.10. White Skin Blotches (links to aquariumscience.org)

11.11. Red Skin Blotches (links to aquariumscience.org)

11.12. Neon Tetra Disease (links to aquariumscience.org)

11.13. Slime Coat Disease (links to aquariumscience.org)

11.14. Scaly Skin (links to aquariumscience.org)

11.15. Fish Not Eating (links to aquariumscience.org)

11.16. Aggression (links to aquariumscience.org)

11.17. Black Death (links to aquariumscience.org)

11.18. Black Head Syndrome (links to aquariumscience.org)

Psuedotropheus crabro Bumblebee Cichlid
Psuedotropheus crabro Bumblebee Cichlid

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Translated in dutch by : Joost Abrahams
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