In the dangerous expanses of open water, it can pay to be a small fish. So small, in fact, that you can hide in a snail shell. Meet evolution’s curiosities from Tanganyika.
WORDS: NATHAN HILL
Based upon chutzpah to bodyweight ratios, the shell dwellers of Lake Tanganyika will always get my vote as the bravest fish in the world. Whether their brazenness really is courage or just stupidity is hard to pinpoint, but they have a vicious streak wider than the lake they inhabit. Keep some at home, and I guarantee that they will bite you one day.
Being bitten by one of the ‘shellies’ is actually pretty cute, thanks to their pygmy statures. The normal impression of a fierce cichlid is some burly, biting submarine of a thing, like the heavyset curs of Central America — the kind of fanged apex predator that has little to fear to begin with.
Shell dwellers tear this impression apart. They are small fish, among the smallest cichlids in the world, and they carry overtones of prey, not predator. But their hearts are those of berserkers, and they will dash headlong into the face of an intrusive human diver, to land a menacing bite upon the tip of the nose. Make no mistake, they want you dead. If every fish in the world behaved like these, then we humans would never have set foot into water. Our boats would be torn out from underneath us, like an aquatic remake of Hitchcock’s ‘The Birds’.
In order to live up to the name of ‘shell dweller’ a fish needs to be pretty small, and their dinky size is advantageous when it comes to seeking out real estate. Curling up inside the curves of a snail shell is a great way to make yourself trickier to swallow.
Tanganyika is the hot spot for fish that live this way, though it’s not the only place it happens. In neighbouring Lake Malawi there’s another cichlid — Pseudotropheus lanisticola — that has also worked out the value of diving into these makeshift caves. Hermit crabs around the world are famous for commissioning shells of all kinds for themselves. But the shell dwellers of Tanganyika take living in old snail husks to an all-new level, making up large urban sprawls — shell cities — with their ad-hoc buildings.
There are different levels of shell dependency between species, and different social structures are built around them. A fish may be facultative, and only use a shell temporarily, if at all. Or they may be obligate, unable to fend for themselves in the lake if they are denied one.
The real surprise of shell dwelling is that it hasn’t evolved as a wider trait. Soft, small fish have long sought solace from larger mouths, and when caves are lacking it’s usually a case of improvise, swim away, camouflage or be digested.
There’s more to shells than just defence. Having all of your neighbours in easily recognisable homes makes it all the easier to keep tabs on who’s who — who has stayed and who has strayed. For the kind of male fish that likes to keep a harem, it’s the ultimate in family enforcement, allowing control and surveillance of a population.
Socially, shell dwellers may live in vast colonies, or they may live in small, pocketed outreaches. There may be a degree of respect for territorial boundaries, or they may behave like warrior tyrants, stealing females and shells from each other, and ravaging their enemy’s fry as they live in a permanent state of hostility.
In Tanganyika, the choice of shell is really only the one: Neothauma tanganyicense. At 6cm/2.4in, this is the largest gastropod in the lake, and the only species in the genus.
Calcium-heavy snail shells are liable to dissolve in fresh water, but because of the intense mineral concentrations within the lake, they last for decades. Neothauma are largish lumps, and successful with it, and their populations can be vast. It’s common to find areas of several square kilometres, with shells strewn like pebbles. In fact, it’s easier to underestimate how vast these shell congregations can be: in places there may be piles of 3m deep. Subsequently, it’s possible to find large areas populated by swathes of shell-dwelling cichlids.
For the aquarist, the appeals are huge. Shell dwellers are, by their very nature, small. That means they don’t require the huge tanks associated with other lake dwellers like mbuna. Because of their sociable natures, species pending, quite large numbers can be kept in relatively small tanks. They feed easily, and breed readily. They have fascinating behaviours worth studying. And if that’s not enough, you can even keep plants in a tank with them. Try that with other African cichlids and see what happens.
To get all of that from one fish, and at the tiny drawback of the occasional comedic nip, I’m surprised that ‘shellies’ are not the most popular African cichlid in the UK. They’re certainly easy enough to house.
Keeping shellies at home
Whichever species you keep, the considerations are basic. First and foremost is tank size, which needn’t be huge. For a single pair of the smallest fish (like Neolamprologus brevis) then a mere 45 x 30cm/18 x 12in footprint is needed. For the largest species, like the beastly, 12cm/4.8in long Lamprologus callipterus, then just 90cm/36in will suffice.
To do things properly, bigger will be better, and will allow you to consider a Tanganyika community with other carefully considered fish. If you want a real good stab at doing a social group of shellies, then consider a tank of 100cm/40in or more. I’ve seen set-ups for these fish of 150cm/60in long, and the fish behaved just like they were still in the lake.
Fine sand is an absolute must. In the wild, these fish dig like crazy. Often it’s the only way they can obtain fresh shells, in the hugely competitive housing market that is shell-dweller city. Avoid coarse coral sand, and plump for one of the finer sands like aquarium silver sand. Some of the ultra-fine, almost dusty substrates like those from JBL are worth a look. Not all of these fish are exclusively shell-inhabitants, and some prefer to dig pits or burrows nearby. A substrate depth in excess of 5–6cm/2–2.4in in some parts of the tank will help them facilitate this.
Decoration is a huge consideration. If you’re housing shellies with other Tanganyikans like Julidochromis, then you need to carefully divide the tank into distinct ‘rock’ and ‘shell’ zones. The problem is this — rock dwellers place an invisible barrier around their rocks, while shellies do the same with their own unique homes. If those territories overlap, the two disputing fish will fight until one backs down or dies.
Just breaking up lines of sight won’t work. If you try placing a visual windbreak between the designated areas, then a rock dweller will try to occupy it, and make a territory around it. It’s considerably safer to leave a clear gap of at least 15cm/6in between the two camps.
Getting the right shells is essential. Too small and the fish will outgrow them rapidly, and then squabble over the remaining few that fit. There will be casualties. Too big or heavy and you’ll deny the fish the ability to move the shells around, ruining a central part of their social dynamic.
It can be tempting to get a bag of assorted marine shells from a retailer and hope for the best, but many of these will be marine whelk types, and far too cumbersome for shellie use. The discarded shells of garden snails can be the right size, though care needs to be taken that they haven’t been contaminated with pesticides. Soaking and rinsing will usually render them safe.
Escargot shells — those from edible snails — are also a near enough size and shape, and can be obtained easily enough from online sources. A soak and a rinse for good measure are still recommended. Whichever shell you opt for, get more than you think you need. Aim for three or four shells for every fish, otherwise there’ll be squabbling.
Being from Tanganyika, the water requirements of all species are the same. You want water that’s harder than trying to read Nietzsche, with an exorbitantly high pH value.
Try to get the pH as close to 9.0 as you can without going over. That means you’ll
want some buffering salts, unless you happen to live with the most caustic water supplies in the UK. A hardness level up around 20°H is no problem here; indeed it may be prerequisite.
Some coral gravel and crushed oyster shell mixed into the substrate, or ocean rock as decor will help to keep pH up, while specially tailored mineral supplements can be used to buffer hardness. Some of them are accurate to a high degree, mimicking the composition of Tanganyika closely, and while not cheap, they do come recommended, especially if you’re considering buying up wild caught fish. Seachem, JBL, Continuum and a heap of other companies have their own products in this line.
Keeping the hardness high is as important as getting it there in the first place, so be wary of factors that can force it down. Trapped food and waste between the shells and in the substrate will have an acidic effect, so regular syphoning of the base is needed. This is when you’ll be bitten most, as the fish will see your hand as a carnivorous intruder, heading down to gobble their eggs and upset their loved ones.
CO2 can have a small but chronic effect, as in high concentrations it lowers pH. Effective gas exchange through surface movement will help here.
Remember that plants aren’t ruled out of a shell dweller tank. These fish are carnivores and uninterested in greenery, and so provided you stick with species able to tolerate the extreme water conditions, then go right ahead. Vallisneria, which struggles in soft tanks, tends to fare well (and some kinds are even found in the lake, making it biotope correct) while the near immortal Anubias, as always, will happily tie to any rocks in the tank.
Aim for filters with ample biological capacity (externals rank highly) as the alkaline conditions of the water mean that any ammonia present will be in its most toxic form. Flow needn’t be directed any which way in particular, but aim for good circulation through the tank. If there’s just enough ‘lift’ to carry particles out from between shells and into the filter, then you’ll save yourself a lot of work.
What to keep with them
Tank mates need some forward planning. Julidochromis, and cylindrical Neolamprologus types may seem the immediate sensible choice, but go sparingly. All of these fish live close to the base and can soon get under each other’s skin.
Higher water fish are worth a look, especially in larger tanks. Aulonocranus is a good choice, and will keep out of the shellies’ way. I’ve seen shellies mixed with Tropheus types before, too, though this requires a vigilant eye.
Stick to fish from the lake. The temptation is to add fish like bristlenose Ancistrus to help curb algae growth, but these are soft water dwellers that struggle with the chronic onslaught of minerals working through their little kidneys.
That’s about as difficult as it gets. If you can provide the above, then you’ve got the makings of a generic shellie tank.
Told you it was easy, didn’t I?
4 shell dwellers for your aquarium
The frog-faced, bulldog-chinned baby of the shell dwellers, N. brevis is one of the more peaceful species. Still, they’ve drawn blood from me on more than one occasion.
N. brevis are small, fierce, and the species you’ll most likely meet in stores. At a distance, their beige colours aren’t too endearing, but observe closely and you’ll spot blue undertones and warpaint splashes of colour over the cheeks. There are a few regional morphs with unique markings, such as ‘sambia’ and ‘katabe’.
As shellies go, they don’t live in vast congregations, and are the wiser choice if you struggle to source an abundance of shells.
Pronunciation: Nee-oh-lamp-row-low-gus brev-iss.
Size: To 6cm/ 2.4in in adult males.
Water: Hard, alkaline: 7.8–9.0pH, hardness 15-25°H.
Diet: Go easy on flakes. Offer lots of brine shrimp, Cyclops, Daphnia and Calanus. Frozen is fine.
Sexing: Difficult when young, males will eventually be larger than females.
Spawning: Add three females to every male, get the temperature up to 25–26°C/77–79°F and condition with hearty feeds of Cyclops. She’ll duck into a shell and lay eggs while he waits at the entrance. As she exits, he fertilises them without even entering. Then he’ll be shooed away and she’ll look after the young. Eggs hatch in around 24 hours, fry are free swimming after a week. Ensure lots of tiny food like infusoria.
Maybe the cutest of all, you definitely want deep sand for these fish. They love to bury their shells, making a kind of funnel around the mouths out of the substrate. This has a double effect of concealing the home, and also encouraging tiny organisms to fall in, like a miniature Sarlacc pit from Star Wars. This second feature is especially handy for raising young.
L. ocellatus are good in large colonies, so don’t be shy about stocking. A 120cm/48in tank with a dozen or more of these shellies is a tremendous sight. Smother the base of the tank with shells and leave them to it.
Pronunciation: Lamp-row-low-gus oss-ell-ah-tuss.
Size: To 5.8cm/2.3in.
Water: Hard, alkaline: 7.8–9.0pH, hardness 15–25°H.
Diet: Daphnia, Cyclops and flake food works well.
Sexing: Look at the fin edges. Males have a gold trim, while females have white. Males are also bigger.
Spawning: Just like N. brevis, except the young get a better start by virtue of the funnel shaped shell openings.
More than likely still sold under the older name of Lepidolamprologus hecqui, this is a shell dweller sitting in the middle of the size ranking. These are easily hefty enough to get your finger in their mouths, so while smaller shellies hit and run, these guys grab and swing.
They’ll form harems, with a male dominating, so if you’re keeping groups then keep eyes open for a straggler potentially being bullied. It happens. If you’re tight for space, they’ll behave just fine as a male and female pair. If they spawn, note that nothing — nothing — will be allowed near them, so if your sneaky Julidochromis are getting a hammering, then it’s safe to say there are young around.
Pronunciation: Nee-oh-lamp-row-low-gus heck-key.
Size: To 8cm/3.1in.
Water: Hard, alkaline: 7.8–9.0pH, hardness 15–25°H.
Diet: Daphnia, Calanus, flakes and pellets.
Sexing: Look at adult faces. Males have a bigger, bulldog jaw and a slight bump on the nose. They’re also physically bigger.
Spawning: A conditioned pair left to their own devices at 25°C/77°F will start going through the motions. Fry hatch in 24 hours, free swimming young appear after five days. Feed meaty foods like Walter worms from the free swimming stage.
The smallest cichlid species in the world? At just 4.5cm/1.8in fully grown, it’s a tiny contender for that humble distinction.
For the shellie fan with limited space, this is the fish to go for. A 45cm/18in tank will house a couple of pairs, or a decent harem for one male. They are easy to keep, easy to source, and cheap enough to buy. If you’re looking for a shell-dweller entry point, I’d definitely choose these!
Pronunciation: Nee-oh-lamp-row-low-gus mull-tee-fash-ee-ah-tuss.
Size: To just 4.5cm/1.8in.
Water: Hard, alkaline: 7.8–9.0pH, hardness 15-25°H.
Diet: Daphnia, Cyclops and flake foods work well.
Sexing: Look at the upper dorsal fin. If it has a red tinge about it, then you have a male. Aside that, wait for them to grow as males are much larger.
Spawning: Just like N. brevis.