Freshwater Fish Disease Information

 Fish Disease
 Bacterial Infections

Prevention of Diseases

Simply put fish need good water quality. This is achieved by good filtration. The primary filter being the biological filter. They like a constant environment stress factors like frequent fluctuations in temperature, and pH stress fish. Water saturated with uneaten food, and excrement can give bad bugs a place to grow and multiply. Fear is also a big stress factor. The fish we keep in aquariums can see you as good as you can see them. In the fish world big fish eat little fish, something to keep in mind. Tapping on the glass, and quick movements outside the tank scares the fish! Fear is often overlooked it can and does cause maladies, from impact injuries, cuts, scrapes, and a weaken immune system. Fish live in a different world where the instinct to flee danger is survival. Secondary bacterial infections can take hold on wounds caused by impact, cut, and scrapes. Giving them a natural setting can help ease the fear, with places to hide. Plants, rocks, and caves make the tank more attractive, and the fish more comfortable. There is a pecking order in your aquarium. Fighting for personal space and food can get out of hand. Watches that the less dominate ones are not getting beaten up. It is not always the larger fish being the most dominate. It is all in the attitude! Overcrowding leads to poor water quality. Improper diets leads to unhealthy fish. External chemical substances like hand lotion, aerosols, window cleaner, and room deodorizers are toxic. I write this not to scare you, but to give you an idea about the world fish live in differs from the world we live in. Good water quality, stable temperatures, and pH and a balanced diet make for a happy aquarium.

Fish Disease

When we suspect something is not right with our fish, we look at them closely. Look at the clear parts of their fins for little white dots sugar like, or look at the whole body for any spots where the slime coat is missing, or just not clear. We look for physical maladies, external parasites, ulcers, skin that is not clear, ragged fins, weight loss around head, or emaciated body. We look for particular symptoms too treat. We see ick we treat for ick. We see a red sore we treat for a bacterial infection, and so on. If there is no physical symptom we look at the water quality. There is only one way too truly diagnose the cause. That is with a microscope. Good lab grade microscopes can be purchased for $200.00. I know this would be for those who a have large investment in their fish. The koi hobbyist have used microscopes as a diagnostic tool for a while now. Those of us who keep aquariums can learn a lot from them. When we treat symptoms this more or less using a shotgun method of treatment. Here at the store we use just a handful of different remedies, compared to the hundreds of medications out there which clam to bring fish back from the brink. To begin with to treat fish, and have success we need to figure out why they got sick. What was the stress factor that caused the malady, and correct that before any treatment will work. Stress factor like temperature, ammonia, nitrite, crowded tank, and aggressive behavior among tank mates. First of all find someone who has experience with the subject, and can explain why they use a particular remedy. In the pet trade anyone can sell these remedies, without any kind of certification, test, or level of experience. Just like the internet information is put out there, and you have to decide whether or not it is a good thing, or a bad thing. Researching the maladies we treat is a good thing; it will make you a more confident aquarist.


At some point most aquarist will experience Ick. Ick is a wicked little bug that can jump your fish when they are stressed. The stress can come in many ways, most common is a temperature fluctuation, adding a new fish, tapping on glass. Ichthyophthirius multifilis (ick) is a ciliated protozoan. The parasite has several phases during it’s life cycle. First embeds in the skin, and gills and matures. Second drops to the bottom dividing into hundreds. Third become free swimming to re-infect the fish. When buried in the skin it is harder to treat. Water changes using a gravel-vacuum after 1st. treatment before 2nd treatment can help with the bottom phase of their life cycle. Medication kills the free swimming phase. Multiple treatments help stop the life cycle. Ick attaches to the skin causing small wounds which can turn into secondary bacterial infections. This can happen very fast 2-3 days, so we need to treat at the first sign of ick, and have the medication on hand to use immediately. Watch for secondary bacterial infections. To make things a little more confusing, there are many different agents out there on the market labeled ick treatments that are not quick enough, do nothing, or even harm our fish. This is a wonderful hobby with a few flaws. Ick can be treated without major losses in most cases. See Medication Page for the treatment we use.

Bacterial Infections

A popular author whose book I read, and re-read states: bacteria do not cause bacterial infections. It has been my experience that this is true. Poor husbandry is generally the cause. In the aquatic environment of our aquariums millions of bacteria live in what looks to be a clean aquarium. Tanks that are neglected and not cleaned on a regular basis can accumulate very large bacterial counts. All bacteria are not bad, but the high count means more and some are bad. Bacteria like Aeromonas, Psudomonas, Vibrio and a host of other bad bugs can grow into very large populations. A somewhat over– simplified explanation these bacteria use nitrogen as a food source. They might start consuming the detritus on the bottom for their nitrogen, but when their populations explode they can start on your fish for the nitrogen they need. A healthy fish, with a healthy immune system ( slime coat ) that is fed good foods, and lives in stable environment generally will not have a problem with bacterial infections. To treat bacterial problems that show up we have to correct the stress factor that caused it to begin with. We start with a partial water change using a gravel-vac. We check the water quality ammonia, nitrite, and nitrate. We check the alkalinity (kH) for bio-filter performance, and to help the fish achieve an osmotic balance. If we do not correct the stress the treatment will not be successful. When we use a shotgun method of treatment (treating symptoms) we use a couple of key agents: Nitrofurazone and Furazolidone. These antibiotics have good absorption and tissue penetration. We have used this combination for years, with good results. It is not too hard on the bio-filter. You should see improvement in 4 days.


Parasites are generally divided into two groups external which live on the skin, mouth, fins, gills, and internal which live in the tissue, blood, organs, and intestinal tract. Parasites can be very difficult to diagnose without a microscope. The fish may flash (rub against objects in tank), look opaque (color off) have thicken slime coats, be swollen or emaciated. Sometimes symptoms are vague. A lot of the parasites are microscopic I understand there are a lot of people who are not going to find an aquatic veterinarian for a few inexpensive fish. When you start trying to find help for your fish you should research from good sources, find people with D.V.M. or PhD. after their name. If you are looking on the internet you should find two sources that agree on both the treatment and agent used. I do not have a degree. I do have many years of experience with tropical fish, and I research my fish often. I write these tips on fish care to give you a starting point. I will give you some links at the end of these tips that can help you find the real experts. When we use a shotgun method of treatment (treating symptoms), salt can be a good starting treatment for parasites. Plain salt (does NOT supply iodine), or have Y.P.S. an anti-cake agent. There are a few fish, and plants that do not tolerate salt very well, discus, some cory cats, otocinclus, Rafael cats, ram cichlids, some small tetras. We can start with a 1% dose which is 1 teaspoon per gallon. We can increase this dose to 3% if your fish tolerate the salt without any stress. 1 teaspoon per gallon added daily for three days. Dose = 3 teaspoons per gallon = 3%. Salt can help with uptake of nitrites by the fish, help with osmoregulation, and help promote heavier slime coats. Salt is inexpensive, does not harm bio-filter, and has added benefits for the fish. Praziquantel is another good agent used in parasite control that works well on some external and most internal parasites. Praziquantel does not harm bio-filers, fish, or plants.

Summary Disease Treatments

To repeat myself a clean environment with good foods, and stable temperature is an important healing factor. If at all possible we need to use agents (medications) That will not harm the bio-filter (nitrifying bacteria). I know this is not always possible, but if it is possible it will help tremendously. There are a few parasites we can see with the naked eye. Ick, anchor worms, fish lice are bugs you can physically see, so we grab the appropriate agent to do the job. In most cases without the use of a microscope to zero in on the bug doing the damage, we have to use a shotgun method of treatment. That is we treat the symptom, rather than the particular bug, doing the harm. Let me throw this out there, having a microscope to diagnose fish maladies can be a good investment for those who have a lot of money in their fish. A good microscope can be had for under $200.00. There is lots of info out there on their use, and identification of the bugs that give us problems. Back to using the shotgun method, when you start trying to find help for your fish you should research from good sources so make sure you find people with D.V.M., or PhD. after their name. If you’re looking on the internet find two sources that agree on treatment, and agent being used. I do not have a degree. I do have many years experience with tropical fish, and I research my fish often. I write these tips to give you a starting point for your research. We try to use percentages in our favor. Example: We know that plain salt kills 80% of the most common parasites that jump on our fish so that is pretty good odds in our favor. I have given you remedies I use for the most common problems we encounter, with the best odds for recovery. I hope this helps.
Thank-You for visiting Darby’s Tropicals.

Good Information Below!
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University of Florida—Tropical Aquaculture Laboratory


Jungle Ick Guard in my opinion the best choice if your fish come down with ick. I have used this product for over 20 years it will not harm your bio-filter, and it works fast. If you have skin fish catfish, loaches or sensitive fish like Black Ghost, Elephant Nose we treat with a 1/2 dose wait 3 hours then treat the other 1/2 dose. I think this should be in everyone's freshwater fish medicine cabinet, to have on hand. Always pull carbon from the system before use. Dose is 1-teasp. Per 10 gallons, Retreat after 24 hours with 1/4 to 1/3 water change, using a gravel-vac. 
Active Agent: (Victoria Green, Nitromersol)
Jungle Fungus Clear is a very good choice. I have used this product with very good success. The active ingredients are antibiotics that are absorbed well, and has good tissue penetration. Always remove carbon from the system, also UV sterilizers will neutralize the active ingredients in this medication. Dose 1 tablet per 10 gallons. Dose is good for 4 days. I like to do a 1/4 water change before use, and again if I retreat. This is another medication to have in your freshwater medicine cabinet.
Active Agent: (Nitrofurazone, Furazolidone)
Jungle Parasite Clear is a good choice for both External Parasites and intestinal parasites. It will not harm your bio-filter. Dose 1 tablet per 10 gallons. Second Dose after 48 hours with 25% water change. Remove carbon before treatment, and U-V sterilizers will neutralize active agent.
Active Agent: (Praziquantel)