Fishkeeping myths that just refuse to die


Nathan Hill rages over some of the rumours, half truths and outright lies perpetuated in the hobby – and the trade.

We’ve all been there, as starter aquarists. The ‘man in the pub’ syndrome is running strong, and everyone who hears that you’ve got into fishkeeping has their tuppence worth to add. And usually their nuggets of wisdom are utter rubbish, nothing but a handful of plastic diamonds sat in a fool’s gold mine.

It’ll only grow to the size of the tank

Seriously, what kind of absolute fool spurts this one out anymore? Of course fish only grow to the size of their tank, that’s why there’s a roaring market for Blue shark pups to go into big aquaria, never getting any more than a couple of feet long. Utter bilge.

Of course, like so many myths, there’s a foundation of semi-truth about this line. Let’s take the humble goldfish as an example, and specifically the fact that nobody seems to understand that a goldfish will live in excess of 20 years and eventually become quite the monster.

When people buy a goldfish and stick it into their tiny plastic death-box, they fully expect the fish to last maybe a year or so at the best. In this time, the fish perhaps doubles in size, looking cramped but alive. Eventually overloading the filter (assuming it’s lucky enough to even have one) the hapless goldy’s organs fail, and it carps it (no pun), completing the illusion that it grew to the size of the tank – not having lived long enough to outgrow it – and lived a happy and full life.

Those few keepers who manage to keep their goldy alive, by comparison, find their fish does eventually outgrow the tank, leading to a succession of ever expansive aquaria to cater for their whimsical purchase. But then they tend to find themselves the exception and not the rule.

The other thing that happens is that some fish stunt. Clown loach are a good example of this, becoming grotesque fat lumps with curved backs when kept in too small a tank. Let’s be clear about this; stunting and growing to the size of the tank are two entirely different things. Fish are not some kind of bonsai animal that you can sculpt in miniature, they have growth potential and they want to use it. Stunting plays havoc with immunity, reproduction, and overall health of the fish, which in turn makes it cruel.

And none of us are in this to be cruel, right? I’m looking at you, live fish feeders.

The water should have some salt in it to stop diseases

Brilliant. I love this one, and it always puts me into an elitist comfort zone when it comes up.

Don’t get me wrong, salt is an amazing medication, definitely up there as one of the best. But that’s its best role, as medication. Or in my cooking, where I always use too much and end up dehydrated with shooting pains down my left arm.

Salt dose rates vary massively depending on the disease. Come to think of it, they even vary depending on the particular species of disease, with one strain of skin fluke being more tolerant than another.

If you’re using salt, then there’s a time and a place. By all means, add it when there’s a specific problem, and you know exactly what that problem is. Although I’ll wager that without a microscope you’ll never tell the difference between Gyrodactylus and Trichodina – both of which require different salt dosages.

But don’t just throw the stuff in and hope for the best. That’s the same mentality as taking a handful of prescription medications on a whim and hoping for the best. And I can tell you now that handfuls of meds don’t work. They just make you vomit blood and go blind in one eye.

On top of not doing anything, incorrect salt dosage is detrimental, and the level at which it can become a problem varies between fish species.

You might not think this possible, but fish can actually dehydrate, and it’s not pretty. Sunken-eyed goldfish from excessive salt use are something I encounter all too frequently, often in retailers.

Worse still, some pathogens are actually helped along by a little salt. I wrote an article in May’s PFK explaining how growth of some skin flukes is actually sped up and assisted by the ‘standard’ dose rate of 3g of salt per litre.

And just as the final thought, once you’ve started to add salt, how do you know how much is in the water? Salt meters aren’t the cheapest of things, and sometimes not so accurate either.

Just pouring in and hoping for the best? Pack it in.

Snails in the tank are bad

Here’s the deal; I love snails. I wouldn’t marry one unless it was really hot, but I still have a soft spot for them.

Most people hate them. They’re dirty, parasitic things that devour plants and ruin the tank. Except they’re not.

Snails tell me something far more sinister about an aquarium. They tell me that you’re keeping it badly. In fact, be grateful for the snails. If they weren’t there you’d have a bigger problem.

Most snails like to chow down on soft, slimy stuff. Absolute favourites tend to be algae, fish food and lovely, rich faeces. Their spiky radula doesn’t really like carving through the hard, cellulose walls of plants, but give them a dying leaf and they’ll take it.

So where does this delight of gastropod gastronomy come from? Rubbish tank husbandry normally does the job, with lashings of overfeeding playing its part. If you’re not gravel cleaning then there’s the problem right there. All that lovely food left behind? Of course the snails are going to exploit it.

What if the snails weren’t there? What would happen then? The fact is that your water quality would be truly up the spout, with rampant phosphates and nitrates doing their thing. Those little shelled molluscs take all the garbage that you should be removing from the tank and they lock it up in their bodies, safely out of the way, right up until you hurl in a load of snail killer and release the lot back into the water. And then you’ve killed off the only thing that was keeping the tank clean for you, so it all goes belly up after that.

I have shedloads of snails in my planted tanks, and I wouldn’t shift them for the world. Half the time, they seem to do a better job than my lazy-arsed shrimps which just sit in the plants all day awaiting their pellets, and uprooting my Glossostigma. I have so many because I’m so liberal with the amount of food that I use to fatten up my fish. It means I need to do more water changes than usual, but my tank is certainly not sat on death’s doorstep, if I might be so bold as to say so myself.

Catfish keep your tank clean

Yeah, right, in the same way that my dog doesn’t keep my house clean. He’ll eat the good stuff when I drop it, and sometimes he’ll just take it straight off of the plate while I’m distracted sorting out a film to watch, but he sure as hell doesn’t clean the place up.

Catfish don’t keep your tank clean. They’re not scavengers, they need their own food, and often food of a very specific variety. A similar claim I often hear is that catfish will keep the tank clean of algae, so that you need never wipe the glass. I’d like to meet said catfish.

The usual victims of this gibberish are those cute aquatic kittens, the Corydoras. Often seen hollow bellied on the base of a tank, these chaps do indeed pick up any uneaten food that manages to run the gauntlet of flake guzzling tetra, but all too often they are overlooked as needing something of their own. They certainly don’t feed on faeces, and as for dying plant matter – forget about it!

Stop being lazy. If you can’t be bothered to do the few minutes of weekly syphon and gravel cleaning to keep the tank healthy then you shouldn’t be keeping fish. There, I said it. We can all find the time to clean our tanks. Don’t expect the cats to do it for you.

Is that the best you’ve got, Nathan?

Well, no. There are loads more things I could whinge about. I could rant about the necessity of airpumps, the legend that smaller tanks are easier for beginners than bigger ones, the frankly preposterous notion that you can wean fish to different temperatures if you do it gradually (so, in effect just kill them slowly), or even the heaving, razor-toothed whopper that states that you can keep armoured catfish in an aquarium with piranha.

But I’m not going to. I’ve got some of the worst ones off of my chest, and I’m sure that nearly anyone could think of a few more that I’ve totally left out – possibly for the reason that they’re so absurd I can’t even be bothered to give them page presence for fear that they’ll be taken seriously.

Why not take out a subscription to Practical Fishkeeping magazine? Check out our latest subscription offer.