I had a doctor's appointment this week and jammed a Killifish Journal in my pocket to catch up on my reading while I waited. In it, I found an article on pathogens identified as Aphanomyces invadans or A. laevens, both molds. The author, Bela Nagy, one of the most interesting fish researchers out there, had identified them from wild caught annual Nothobranchius killifish caught in polluted waters in East Africa. If you last thorough this post, you might recognize things here. My fish collecting friends and I saw the same thing in Gabon in 2023, though we didn't test the fish. We caught a couple of Epiplatys singa in a still, foul stagnant pond left over as a stream had dried up. They had a thick slime growth on their backs, and their tails were eaten away. The disease worked on the bagged fish, killing them within minutes.
We chalked it up to what we as hobbyists call Columnaris.
The fungus that's really guilty sounds like what used to be a common disease. I've kept fish for 59 years, and seen a few diseases as well as patterns of diseases. I like to think I've seen things, but also noticed them, due to my 86 year old mentor when I was in my teens being an aquarist who taught me about fish diseases. So here we go.
Mr Nagy notes that what I translate to "cotton disease" in English (the article is in French) is a mold that generally feeds on detritus and debris in water. It only settles on fish if the environment changes, but it is a major issue in aquaculture ponds and for fish in degraded habitats. It likes soft muddy substrates, low oxygen, temperatures between 18 and 22c, and pollution, especially if there is a change in water quality. Rains stirring up the substrate count there. Once on the fish, it causes cottony growth, then ulcers, and kills. Fish aren't its target in life - it likes all decay.
In the 1970s to the mid 1980s,this was something I saw a lot of. I was a curious aquarist who never passed an aquarium store without taking a look, and I had been taught how to look for diseases and parasites. I saw it often, especially in feeder tanks. Meds for it were commonly available - acriflavene based yellow/green dyes since proven to be potentially carcinogenic in larger doses than we used. They weren't too successful unless we caught it really fast, or unless we encountered something similar to Aphanomyces, but not as deadly.
The disease largely faded out of sight with the advent of the water change era, although I'd never put two and two together on that til this week. I've still seen it in feeder tanks, as those are among the most abused fish in the trade.
So what's the newest fad in fishkeeping? I live in a region where most new aquarists start with internet info, usually from youtube gurus. They seem to think they can recreate nature in 20 gallons of indoor boxed water. That's fair: so did many like me in the balanced aquarium era of the 1970s. Mud bottoms are in. Accumulating mulm is in. No filtration (filters in unnatural glass boxes aren't natural). No water changes because, well, umm, laziness is in. Overstocking because they take the online calculators, which start by trying to sell fish and expect you to have a filter. If I were an Aphanomyces mold (not my ambition) I couldn't think of a better place to be.
And what am I hearing? There's an awful new fish disease that makes the fish all cottony. So like measles for the kids of those who don't get them vaccinated, it's coming back.
All right, I'm editorializing. Mr Nagy is much more clinical in his excellent article. With me, it provoked thoughts.
Killi-Revue Juillet Aout 2025, Bela Nagy, Decouverte d'agents pathogenes dans des populations sauvages de Nothobranchius. (Discovery of pathogens in wild Nothobranchius populations). Killi Club de France.
We chalked it up to what we as hobbyists call Columnaris.
The fungus that's really guilty sounds like what used to be a common disease. I've kept fish for 59 years, and seen a few diseases as well as patterns of diseases. I like to think I've seen things, but also noticed them, due to my 86 year old mentor when I was in my teens being an aquarist who taught me about fish diseases. So here we go.
Mr Nagy notes that what I translate to "cotton disease" in English (the article is in French) is a mold that generally feeds on detritus and debris in water. It only settles on fish if the environment changes, but it is a major issue in aquaculture ponds and for fish in degraded habitats. It likes soft muddy substrates, low oxygen, temperatures between 18 and 22c, and pollution, especially if there is a change in water quality. Rains stirring up the substrate count there. Once on the fish, it causes cottony growth, then ulcers, and kills. Fish aren't its target in life - it likes all decay.
In the 1970s to the mid 1980s,this was something I saw a lot of. I was a curious aquarist who never passed an aquarium store without taking a look, and I had been taught how to look for diseases and parasites. I saw it often, especially in feeder tanks. Meds for it were commonly available - acriflavene based yellow/green dyes since proven to be potentially carcinogenic in larger doses than we used. They weren't too successful unless we caught it really fast, or unless we encountered something similar to Aphanomyces, but not as deadly.
The disease largely faded out of sight with the advent of the water change era, although I'd never put two and two together on that til this week. I've still seen it in feeder tanks, as those are among the most abused fish in the trade.
So what's the newest fad in fishkeeping? I live in a region where most new aquarists start with internet info, usually from youtube gurus. They seem to think they can recreate nature in 20 gallons of indoor boxed water. That's fair: so did many like me in the balanced aquarium era of the 1970s. Mud bottoms are in. Accumulating mulm is in. No filtration (filters in unnatural glass boxes aren't natural). No water changes because, well, umm, laziness is in. Overstocking because they take the online calculators, which start by trying to sell fish and expect you to have a filter. If I were an Aphanomyces mold (not my ambition) I couldn't think of a better place to be.
And what am I hearing? There's an awful new fish disease that makes the fish all cottony. So like measles for the kids of those who don't get them vaccinated, it's coming back.
All right, I'm editorializing. Mr Nagy is much more clinical in his excellent article. With me, it provoked thoughts.
Killi-Revue Juillet Aout 2025, Bela Nagy, Decouverte d'agents pathogenes dans des populations sauvages de Nothobranchius. (Discovery of pathogens in wild Nothobranchius populations). Killi Club de France.
