Most blood red blotches on the fins or skin of tropical fish are blood under the skin or hemorrhagic septicemia (“Red Pest”), an internal bacterial disease. The bacteria is generally a gram negative bacteria, with aeromonas bacteria being the chief culprit.
Hemorrhagic septicemia is a very serious condition from which fish have very high mortalities, even with antibiotic treatment. Many experienced fish keepers use a “nuclear option” to treat hemorrhagic septicemia, with three treatments done simultaneously: antibiotics in the food, sulfa drugs and/or furans as one-hour baths and sulfa drugs and/or furans in the aquarium water.
There is a disease seen occasionally in pond fish that is a virus-caused septicemia. But there appear to be no confirmed instances of it occurring in the tropical aquarium. This is probably because the virus is only virulent at temperatures below 68 degrees F. (20 degrees C), (“Effect of water temperature shifting on mortality of Japanese flounder Paralichthys olivaceus experimentally infected with viral hemorrhagic septicemia virus”, Sano et al, 2009).
Here are a whole series of fish with bacterial hemorrhagic septicemia:
On particular type of bacterial septicemia is when goldfish get very red mouths. This is “red mouth disease” caused by the bacterium Yersinia ruckeri This is a serious disease that will kill the goldfish if not treated. The disease is treated exactly the same as any other bacterial septicemia. This disease is covered in this article:
“10.3.10. Red Mouth in Goldfish”
Here are two goldfish with red mouth disease:
Red blotches such as these are most often septicemia caused by gram-negative bacteria (aeromonas, columnaris, etc.). The blood-red patches are obviously just under or in the skin and scales of the fish. And the color varies from bright red to brownish red.
Note that carbon dioxide/ammonia poisoning during shipment can be mistaken for septicemia. The hemorrhages of carbon dioxide/ammonia poisoning are internal, typically inside the body cavity. The appearance of ammonia poisoning is quite different than septicemia. The ammonia builds up internally inside the fish. The ammonia inside the fish causes the internal organs to bleed. The body cavity (i.e. the belly) will take on a purple/red hue from blood. This purple/red color is much different than the brownish-red blotches of septicemia.
Invariably when a posting comes on social media of a fish in an aquarium with obvious septicemia or even saddleback there will be several commentators who will chime in with “That fish has ammonia burn“. First off ammonia poisoning is actually extremely rare in aquariums. And it presents much differently than septicemia. The color is different and it is internal inside the fish, it does not occur in the skin or on the scales of the fish.
Hemorrhagic Septicemia should be treated with broad-spectrum antibiotics (Midland Vet Service Aqua-Mox, VetDepot Amoxicillin, Fishbiotic Ampicillin, Mardel Maracyn 2, SeaChem KanaPlex, API Fin And Body Cure).
These medications are only available over the Internet. Fish stores have all gone over to “natural” medications which have a very high profit margin and simply put, don’t work.
Bacterial infections are most effectively treated with antibiotics in the food. Many believe (and the instructions on the antibiotics say!) that antibiotics need to be added to the water. They are simply incorrect. This controversial topic is covered in the following link:
It is easy to make medicated food. Heat 1/4 cup water (two ounces or 58 milliliters, not a lot) in the microwave. Then blend seven grams of plain animal-derived gelatin (Knox gelatin, one packet) into the hot solution with vigorous stirring. Take two tablespoons of dry commercial fish food (pellets or flakes) and mix it with just a little of the hot water/ gelatin mixture. Add hot water/gelatin until you get a paste-like consistency. If it gets too watery just add more food. To get gel food to float simply mix in a little whipped cream at this point.
Then add just a “smidgen” (roughly 1/16 teaspoon, a 1% to 2% addition) of medication to the mud. If you are using more than one medication mix the medications together, then use just a “smidgen” of the mixture. If you are using a packet of medication, take just a “smidgen” of the packet’s contents. Mix and mash the whole mass thoroughly.
All the fish in the aquarium should be fed a steady diet of antibiotic-laced food for at least ten days. Note that the exact amount of medication that goes into the food is not very important. Antibiotics can be overdosed pretty much with abandon as they are only toxic in large doses over a period of months. Note antibiotics in the food do not affect the filters so they can be left in place and operating.
If you can’t resist the urge to treat the water, remove the biofiltration media (including sponge and/or foam) in the filters and put it in an open container for the duration of the treatment. Sometimes antibiotics kill the beneficial bacteria and sometimes they don’t. In any case, the filter media will denature the antibiotics. Monitor the ammonia and would do a 50% water change if it spikes above 1 ppm. Reduce the amount of food fed by 2/3 rds.
Note that if antibiotics are not available, it is quite easy to take a pill or capsule of human antibiotic and use it for fish. If it is a pill just grind it up. Just be aware that human antibiotics are about ten times more potent than aquarium antibiotics, so just a “smidgen” in the food is more than enough. This is a very good option for the folks in Europe or Canada, where fish antibiotics are illegal.
The “Nuclear Option”
Any internal bacterial infection that has become advanced enough to cause hemorrhaging under the skin of a fish is a very advanced bacterial infection. The mortality rate is going to be very high no matter what the treatment. It is always difficult to tell a fish keeper their fish are probably going to die but with hemorrhagic septicemia that is just the “cold hard facts”.
Many experienced fish keepers use a “nuclear option” to treat hemorrhagic septicemia, with three treatments done simultaneously:
- antibiotics in the food,
- sulfa drugs and/or furans as a one-hour baths
- sulfa drugs and/or furans in the aquarium water.
There is only anecdotal evidence that this works but if one is so inclined one can do it.
We cover antibiotics in the food above. Here is how to use the sulfa drugs or furans.
Sulfaguanidine, sulfathiazole, sulfamethazine and sulfacetamide are all that are called “sulfa drugs”. Mardel Maracyn Plus is a combination of two anti-bacterial drugs, sulfaguanidine and trimethoprim (trimethoprim is an antibiotic with an action that is very similar to furans). SeaChem SulfaPlex (Sulfathiazole) is a sulfa drug. API Triple Sulfa (Sulfathiazole, Sulfamethazine and Sulfacetamide) is a sulfa combination.
“Furans” include nitrofurantoin, nitrofurazone and furazolidone. Bifuran is nitrofurazone and furazolidone. SeaChem Focus is “polymer-bound” nitrofurantoin. Sulfa and furans have very similar properties with furans being more toxic to fish than sulfa drugs,
To treat a fish with hemorrhagic septicemia, make up a bath with a sizable dose of the furans or sulfa drugs. Use five times the recommended dosage of a furan drug or ten times the recommended dosage of the sulfa drug. Put the fish in the heavily dosed water for one hour and only one hour. Then return the fish to an aquarium. Repeat this once every 24 hours, no more.
Then follow the directions on the package of furans or sulfa drugs as to adding the medication to the aquarium water. This dosage in the aquarium water will not bring up the level of the drug in the fish to therapeutic levels but will prevent the bacteria from being transmitted from fish to fish.
If one has more than one fish with a bacterial disease, one must treat the whole aquarium. This is an emergency. Don’t fool around with herbs, tree leaf oils or some ineffective treatment. Ben Ochart treated a bacterial infection with Pimafix and Melafix. They did nothing to stop the infection. He lost a lot of large beautiful fish before he stopped the infection with antibiotics and sulfa drugs. This link covers the snake oil medications such as Melafix and Pimafix:
The entire topic of bacterial infections in tropical aquarium fish is covered in more detail in this link:
Source: Aquariumscience.org – David Bogert