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10. Diseases

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Author : David Bogert

Published :

Time To Read :
5 minutes
Difficulty : Level 5

Excerpt :

This is a listing of a series of article on the diseases of tropical fish.
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

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

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

10.2. External Protozoans

10.2.2. Ich

10.2.3. Velvet

10.2.4. Epistylis

10.2.5. Chilodonella and Costia

10.2.6. Tetrahymena

10.2.7. Cryptobia

Tropheops Red Fin Puulu
Tropheops – Red Fin Puulu

10.3. Bacterial Diseases

10.3.1. Skin Ulcers

10.3.2. Mouth Rot

10.3.3. Duck Lips

10.3.4. Fin Rot

10.3.5. Saddleback

10.3.6. Red Blotches

10.3.7. White Eyes

10.3.8. Pop Eyes

10.3.9. Red Gills

10.3.10. Red Mouth in Goldfish

Synodontis multipunctatus
Synodontis multipunctatus

10.4. Tuberculosis (Fish TB)

10.5. Hexamita

10.6. Flukes

10.7. Fish Saprolegnia or “Fungus”

10.8. Lymphocystis

10.9. Anchor Worms

10.10. Black Spot

10.11. Tapeworms

10.12. Nematodes

10.12.1. Camallanus

10.12.2. Capillaria

10.13. Pests in the Aquarium

10.14. Fish Lice

10.15. Dwarf Gourami Disease

10.16. Graphite Disease in Bettas

Selenotoca multifasciatus Silver Scat
Selenotoca multifasciatus – Silver Scat

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

12.1. Basics of Treatment

12.2. Various Treatments Summarized

12.3. Quarantine Tanks

12.4. Ineffective Medications

12.5. Fish Don’t Drink

12.6. Sterilization

12.7. Making Medicated Food

12.8. Euthanizing a Fish

12.9. Avoiding Fish Diseases

12.10. The “Shotgun” Approach

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

11.2. Stringy White Poop

11.3. Malawi Bloat

11.4. Dropsy

11.5. Hollow Belly

11.6. Swim Bladder Disease

Rineloricaria parva Whiptail Catfish
Rineloricaria parva – Whiptail Catfish

11.7. Shimmying

11.8. Twirling

11.9. Spinal Deformities

11.10. White Skin Blotches

11.11. Red Skin Blotches

11.12. Neon Tetra Disease

11.13. Slime Coat Disease

11.14. Scaly Skin

11.15. Fish Not Eating

11.16. Aggression

11.17. Black Death

11.18. Black Head Syndrome

Psuedotropheus crabro Bumblebee Cichlid
Psuedotropheus crabro – Bumblebee Cichlid