Do catfish eat whitespot? Research says 'maybe'...


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Some things just seem intuitively obvious — although not until they've been pointed out to you. Suckermouths reducing whitespot is one of those very obvious things, and now somebody has pointed it out! Nathan Hill investigates.

I'm sure there are those out there that will say they've seen this all before, and that they've known about this for years. Go right ahead, I say. The report in question was only published in February this year, and makes it quite explicit that such an experiment has never been performed before. So there. It’s never been official.

It’s no secret that many of the scientific advances in aquatics are a spill over from either the wastewater industry, or aquaculture. Much of what comes out of these domains is of limited use, but every so often we get a real gem.

The upshot of experiments performed by Sara Picon-Camacho et al in a recent paper, is that our humble Sailfin suckermouth catfish, Glyptopterichthys gibbiceps, could be a potent biological control of freshwater whitespot, Ichthyopthirius multifilis.

To understand how this might work, I’ll need to give the fastest crash course on the whitespot life cycle ever. Brace yourself.

Whitespot, when it’s visible on a fish is buried under the skin, deeper than an Alabama tick, and you cannot touch it with a treatment while it’s there. One company told me that they could treat it under the skin, but when I pressed them on it they just giggled like little girls and pretended they didn’t understand me.

After it has gotten fat on your fish, it bursts out of the skin, floats around in the tank for an hour, and then sinks to the bottom. For this one hour, it is susceptible to whitespot treatments, which doesn’t help given how long they take to act.

Once on the bottom it turns into a baby whitespot factory, hunkering down in a protective cyst and creating up to 3,000 little daughter whitespots. While it’s cysted up and multiplying, chemical treatments won’t touch it.

These then rupture out in a blizzard of infection and swim off to find a new host – at this point you can treat, but it’s a running battle of sorts between the baby cyst being exposed long enough to the treatment, or finding a host and burrowing in – at which point it’s untouchable again until the next cycle.

So now you understand whitespot. Sort of.

In aquaculture, they don’t even have the benefit of using effective medications, especially since Malachite green was banned on any kind of food fish. They need to find other ways of keeping it in check, and given the huge stocking densities in which fish farmers tend to keep their fish, whitespot is often something of an inevitability.

Catfish cures?

So how on earth do Sailfin plecs help? Well, the theory is that when the catfish grazes on biofilm, it does something that upsets the resting cysts within it. For whatever reason, whitespot is more attracted to biofilm than not (as well as lighter coloured substrates, if you didn’t know), and it’s the biofilm that Sailfin plecs like to grub about in and eat.

It could be as simple as the catfish eats the cyst. Digesting stomach acids are pretty harsh things, and even if a treatment won’t touch a cysted whitespot, a good dose of gut activity might.

However, it could be that the cysts don’t like being disturbed. They may react badly to being knocked back up into the water column, or even being moved about while they’re multiplying.

Either way, gibbiceps make a difference.

What did the research find?

The experiments in question involved taking Oreochromis aureus that could be infected with whitespot, and placing them either in aquaria with or without the catfish in tow.

The exact rates of fish used in the experiment were one gibbiceps to every 4.5 Oreochromis, and it’s worth mentioning that these were not big Sailfins, by any standards. The average weight of the specimens used hovered around the 2.5g mark, so don’t think that this is just something that large plecs can pull off.

The eventual figures turned out to be surprising. The Oreochromis that were kept in with the Sailfins carried infestations of 63% less than those that were kept absent from the catfish. That’s a pretty big result for fish kept over the same period, and in parallel conditions the whole time.

Interestingly, researchers also found that the immunity of the gibbiceps was higher than that of the Oreochromis to the whitespots. It is suspected that the very nature of the catfish armour lends itself to fighting off these parasites better than many other fish, although this has yet to be verified. The researchers express an interest in discovering different loricariids with an even better immunity to whitespot.

Past, present and future?

Traditionally, biological controls have been tried with fish many times before, although almost exclusively marine fish in pens. Cleaner, Corkwing, and even Goldsinny wrasse have all been previously used to keep ectoparasites in check, and for the larger parasites at least they have some effect. But individual whitespot (albeit, the marine version, Cryptocaryon) have always been harder to stop.

The ramifications for controlling whitespot with hardy catfish should hopefully have huge implications for a chemical free method of rearing farmed freshwater fish. So what about we aquarists?

Well, let’s get one thing straight from the offset, if you’ve got whitespot in your tank then under no circumstances go out and buy a catfish to put in it. I’ll write that again so there’s no confusion. I’ll even put it in bold:

Do not buy a catfish if you have whitespot in your tank!

Whitespot in aquaria is more often than not the result of poor water management, and a product of compromised immune systems. Adding a catfish will not impact the underlying cause of whitespot, and all you’ll be doing is sending a naïve fish off to a guaranteed infection, or maybe much worse.

However, as a possible preventative, or even as potential inhabitants in quarantine tanks, there could be mileage in anything that eats/upsets whitespot cysts. The thinking is that it’s not just gibbiceps that can upset multiplying whitespot cysts. Any kind of detritivore, algae grazer, or substrate feeder could have a potential effect. Hopefully more research will reveal who’s the best, and how they’re doing it.

And finally, it looks like it might not just be whitespot that the catfish upset. Potentially, the same activity might be applied to reduce other aquarium nasties like Cryptocaryon, Amyloodinium, Chilodinella, and Piscinoodinium.

If you fancy a look at the article yourself, then you can find it right here – although you’ll need an account, or some other mode of journalistic access. This one isn’t a free paper just yet…