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Tanganyikan Shell Dwellers: Fun fish for the small aquarium
The “shell dweller” cichlids of Lake Tanganyika are a group of small fish that spend all their time in and around empty snail shells. Because their maximum length is less than 5 cm and they defend comparatively small territories, they are relatively easy fish to house. Even tanks as small as 37 litres (10 gallons) can house a colony of these diminutive cichlids.
Besides being small, they’re also active and attractive fish. Most are pinkish-brown to golden yellow in colour but marked with flashes of blue, yellow or black. Compared with other cichlids, territorial aggression is limited to defence of the shell, and provided each fish has its own shell, serious conflict is unlikely. While they can’t be kept with other bottom-dwelling species such as catfish or loaches, shell dwellers get along fine with species that stay at the surface far away from their precious shells. Small livebearers such as Endler guppies or platinum halfbeaks for example would make ideal companions.
All things considered, these fish would seem to be ideal aquarium inhabitants, and to some degree this is true. But like all Tanganyikan cichlids they are sensitive to poor water quality and require very specific water chemistry conditions to do well. They aren’t standard issue community fish by any means, but rather something for the more experienced hobbyist looking to create a small but interesting species aquarium.
In the wild shell dwellers live around the shoreline of Lake Tanganyika in habitats where the water is crystal clear and well oxygenated. They feed primarily on zooplankton that they snap up from the water column as it drifts by (in this sense, they’re rather similar to things like the jawfish familiar to marine aquarists).
Most species live in colonies where one male maintains a territory containing the shells of several females. The male has his own shell, but slips into the shells of the females in his harem each time he spawns. Mostly, it’s the female that looks after the eggs and fry, though the male will be defending her territory alongside his own. These are the polygamous shell dwellers and include species such as Lamprologus ocellatus.
Some shell dwellers form monogamous pairs. The species Neolamprologus brevis is the best known example of this type. Males and females spawn within a shared shell, and both parents defend the eggs and fry. By contrast with the polygamous species, monogamous species tend to be somewhat mellower, and multiple pairs may be maintained in one tank without much bother.
Water chemistry requirements
As with any other Tanganyikan cichlid, the shell dwellers need water that is hard and alkaline. Carbonate hardness is critical, both for raising the hardness level itself but also because it will raise the pH to the right level, and inhibit acidification (pH drops) between water changes. Aim for 7+ degrees KH and a pH between 8.0-8.5.
The easiest way to ensure the correct water chemistry is to add Rift Valley salt mix to each bucket of new water. Commercial formulations are available, or you can make your own salt mix by dissolving 1 teaspoon baking soda, 1 tablespoon Epsom salt and 1 teaspoon marine salt mix to every 20 litres (5 gallons) of water. Before adding the water to the aquarium, use your test kits to ensure the water chemistry values are correct, and if necessary add more water or mineral salts as required.
Many aquarists incorporate carbonate-rich materials in the aquarium, specifically coral sand and crushed coral. When combined with an undergravel filtration system, the slow dissolution of these materials will raise the pH and carbonate hardness to appropriate levels. The downside to this approach is that over time dirt and bacteria will coat the sand and coral fragments, reducing the rate at which dissolution can occur. It is important to check the water chemistry periodically, and if necessary clean or replace some of the calcareous material.
Whichever method you decide to use, it’s important to regularly test water chemistry. Between water changes, pH drops through a process of acidification caused by the decay of organic material. In an ordinary community aquarium, regular water changes offset these pH changes before the fish come to any harm. But Tanganyikan fish are much more sensitive to pH changes than standard community fish, even hardwater species like livebearers. The background pH drop between water changes will severely stress them, and sudden pH rises that occur during water changes are just as bad.
The art to keeping Tanganyikan fish like shell dwellers is to ensure the water contains lots of carbonate hardness. If you’re relying on calcareous media alone to harden tap water, take care not to do excessively large water changes at any one time. Replace a relatively small quantity of water, no more than 25%, and check that the pH before and after the water change is not substantially different. By doing small water changes, you’ll allow time for the calcareous media in the tank to dissolve and raise the hardness of the new water.
If you’re using Rift Valley salts of some type, then the incoming water will be adequately hard and basic already, so your main problem is ensuring that pH hasn’t dropped too far between water changes. In tanks without calcareous materials to further buffer any pH changes, it’s important to keep water changes regular and substantial, with changes of 50% per week not being excessive. Again, regular use of your pH test kit will help you keep track of water chemistry between water changes.
Because of the need to harden the water and raise the pH, it isn’t a good idea to use bogwood in the shell dweller aquarium.
Cichlids generally are intolerant of ammonia and nitrite, but Tanganyikan cichlids add severe sensitivity to nitrate to their list of requirements. For long term success, the nitrate level should be kept below 20 mg/l.
Regular water changes will dilute the amount of nitrate in the water, and low stocking levels and careful control of food will minimise the rate at which nitrate levels go up. But in many parts of the UK, the nitrate level of tap water may be unacceptably high for these fish. The maximum safe level of drinking water is considered by the government to be 50 mg/l, and all tap water supplies should contain less than this amount. Precisely how much nitrate the water will contain varies, but in urban areas particularly, tap water can easily contain between 40-50 mg/l nitrate.
There are two ways to work around this problem. The first is to use a de-ioniser or reverse-osmosis filter to turn tap water into very pure, nitrate-free water suitable for use in the Tanganyikan cichlid aquarium. Although expensive, this approach is convenient and safe. The alternative is to collect rainwater. While much cheaper to set up and effectively zero cost to use, rainwater has the potential to pick up atmospheric pollution and should be filtered though carbon before use. In either case, the nitrate-free water is also mineral-free, so a Rift Valley salt mix will need to be added to the water to create the right water chemistry conditions.
In terms of nitrite and ammonia, any decent biological filtration should do the trick. Ample water flow is recommended though, both to ensure quick processing of nitrogenous wastes and to keep the water in the tank well circulated. Because these cichlids are intolerant of ammonia and nitrite, ensure the filter is fully matured before use, for example by filling it with substantial amounts of live media taken from an already cycled aquarium.
These cichlids do best at fairly high temperatures, between 25-28 degrees C (77-82 degrees F) being recommended. Because oxygen concentration drops as temperature goes up, it’s important to ensure the tank is not overstocked and that the water is properly circulated through the use of brisk filtration. Supplementary aeration may be useful in summer if the water gets particularly warm.
Under aquarium conditions, shell dwellers are essentially opportunistic omnivores. To avoid problems with vitamin deficiency, it is sensible to offer a variety of foods. A good quality cichlid-specific flake food would make a good staple, alongside regular supplies of frozen and live foods including brine shrimp, daphnia, lobster eggs and small bloodworms.
These fish are primarily zooplankton feeders, and prefer to take foods drifting by in midwater. Like most other plankton-eaters, they do best when given regular but small meals rather than large amounts once a day.
As noted earlier, shell dwellers are divided into the harem-forming polygamous species and the pair-forming monogamous species. In general it isn’t a good idea to mix species, in part because of the risk of hybridisation, but also because different species may have incompatible social behaviours. So when setting up a shell dweller tank, it’s best to choose a single species and stock it in appropriate numbers to minimise intraspecific aggression.
Polygamous species are best kept in groups of six or more, at a density of about six fish per 37 litres (10 gallons) of aquarium space. All fish should be introduced at once, ideally as juveniles, into a tank with a fully matured filter. Sexing juveniles is generally difficult, but as the fish age, it should become clear which fish are females, which fish is the harem-holding male, and which males are surplus to requirements. In a very large tank, it may be possible to have more than one harem-holding male by placing clumps of shells at different ends of the tank, but otherwise surplus males are best removed, particularly if they show signs of being bullied or damaged.
Monogamous species can be introduced as groups in the same way as polygamous species and left to pair off naturally. However, they are best kept as a single pair in a 37 litre (10 gallon) tank of their own, though you could combine with suitable midwater dither fish if you wished.
All shell dwellers lay their eggs inside empty shells, with parental care varying depending on whether the species is polygamous or monogamous. Only among the monogamous species will males show any (albeit slight) interest in defending their spawn. One unusual aspect of shell dweller breeding behaviour is that the females often initiate spawning, actively “flirting” in front of the males in a manner reminiscent of some of the West African cichlids such as Pelvicachromis.
Regardless of the species, breeding is essentially similar for all of them. A typical spawning results in up to 100 eggs, and these are placed far back inside the shell. Indeed, a good sign spawning has occurred is the seeming disappearance of the female while she protects and cleans her eggs. Hatching occurs about one week after spawning, and the fry quickly being feeding on infusoria, brine shrimp nauplii, microworms and artificial (liquid or powder) fry foods.
Healthy females will spawn as often as every six weeks, and the fry will generally be ignored after about three weeks post-hatching. Growth is fairly rapid, and by cichlid standards shell dwellers can be considered quite easy to breed.
In the wild shell dwellers favour the shells of the snail Neothauma tanganyicense. But under aquarium conditions most any snail shells of approximately the right size will be readily accepted. Empty apple snail shells are sometimes used, but the most popular shells for these fish are escargot snail shells of the types sold in upmarket grocery stores and delicatessens. Marine snail shells can be used too.
Shell dwellers like to sculpt the area around their shells. The best way to decorate the tank is to provide a substrate of coral or silver sand, scatter the empty shells around the tank, and then let the cichlids dig about as they wish.
Tankmates and dither fish
Shell dwellers are defensive towards bottom dwellers including loaches, catfish and of course other cichlids. They will harass and potentially kill small catfish such as Corydoras, whereas larger bottom dwellers will simply terrify them. But midwater fish are tolerated rather well, if chose carefully. Large midwater species have to be avoided because they will be viewed as a threat. The shell dwellers will spend all their time hiding away in their shells!
Instead, choose tankmates that are no larger than the shell dwellers themselves. Properly selected, midwater fish act as “dither fish”, encouraging the cichlids to swim outside their shells. Good choices include small livebearers, wrestling halfbeaks, dwarf rainbowfish, and hardwater-tolerant minnows such as White Cloud Mountain minnows and danios. Note that shell dwellers can be predatory, and will view very small tankmates (such as livebearer fry) as food.
Lamprologus ocellatus is a very popular shell dweller much loved for its small adult size (around 4-5 cm) and sprightly personality. It is golden-yellow in colour but with a blue sheen across the flanks and a distinctive dark patch on each gill cover. It is a harem-forming species and best kept in a reasonably large group of females alongside a single male. Although males are intolerant of one another, they active defend comparatively small areas, and rarely stray much beyond 15 (6 inches) from their home shell. So in a tank with sufficient space, it may be possible to house more than one male’s territory without problems. This species may also be kept in pairs, though such behaviour is probably uncommon in the wild. Lamprologus ocellatus is widely sold and much of the stock on sale is captive bred. This is a reliable species, and a good choice for beginners.
Lamprologus meleagris is very similar to Lamprologus ocellatus in terms of care, but has a very different colouration. It has the same stocky body shape, but the body colour is pinkish-brown and covered with dark mottling and small, whitish-blue spots. The fins are also very delicately marked with light and dark spots.
Lamprologus signatus is one of the shell dwellers that apparently switches between monogamy and polygamy depending on the situation. Males are bigger than the females at 5 cm in length compared to 3 cm, but otherwise the key difference between the sexes is colouration, males having thin, dark vertical bands on their flanks and fins that are much stronger than those seen on the females.
Neolamprologus brevis is one of the most widely traded shell dwellers. Females only get to a length of 4 cm, while males are a bit larger at up to 6 cm. The sexes are otherwise rather similar, both being pinkish-brown and delicately marked with shiny blue patterns on their face and fins. There are numerous subtly distinct geographical variants as well, some of which turn up in the better aquarium shops. Neolamprologus brevis is unusual in being one of the pair-forming species, apparently an adaptation to environments where empty shells are scarce. Perhaps related to this is the fact that they are very mild mannered by shell dweller standards, and as such make one of the best aquarium species.
Neolamprologus hecqui is one of the larger shell dwellers, males getting to a whopping 8 cm in length. Females are only about half that size though. Some aquarists refer to this species under another name, Lepidiolamprologus hecqui, currently not recognised by scientists as being correct. Whatever its name, this unusual species is impossible to sex when young, so are best introduced as a group of juveniles in a fair sized tank. Provide lots of generously large shells so that this harem-forming species can spread itself out easily. They work best as matched pairs, but because both sexes look so similar when young, you’ll have to raise a group of juveniles together to start with, and then remove any surplus fish in due course. This is a very attractive species though, with a long, torpedo-shaped pinkish coloured body marked with metallic blue spots on the flanks and a distinctive black edge along the dorsal fin and the top of the tail fin.
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