Shell-Dweller Cichlid Tank: Sand, Shells and Tanganyika Water

Setting up a tank for Lake Tanganyika shell-dwelling lamprologine cichlids: sand depth, more shells than fish, hard alkaline water, colony behaviour and suitable tankmates.

What a shell dweller is

Shell dwellers are cichlids that use the empty shells of aquatic snails as shelter and as breeding sites. The term is descriptive and has no formal taxonomic standing. In Lake Tanganyika, along the coasts of Zambia, the Democratic Republic of Congo, Burundi and Tanzania, about 24 lamprologine cichlid species use abandoned shells of the snail genus Neothauma; Wikipedia notes that the largest endemic Tanganyika snail supplies the shells most often used by small shell-dwelling cichlids. Most of these species are not obligate shell breeders and will also spawn in caves or crevices.

Hobby groupings include the colonial shell dwellers (Neolamprologus multifasciatus), the ocellatus group (Lamprologus ocellatus), larger Neolamprologus, Altolamprologus, Telmatochromis, and the brevis and signatus groups. The two most widely kept examples are profiled below.

• Neolamprologus multifasciatus: maximum about 45 mm standard length (SL); field studies report wild males and females rarely exceeding 3.0 cm and 2.1 cm SL respectively. Males are considerably larger than females.
• Lamprologus ocellatus: maximum about 60 mm SL. Males grow much larger than females and have gold-edged fins, while females have white-edged fins.

Shell beds in the wild

Parts of the Tanganyika lake floor are covered by massive accumulations of empty snail shells, called shell beds. Because the shells are usually buried in sediment, N. multifasciatus dig them out and excavate sand from inside them. The scooped-up sand is piled along the borders of each group's territory, building walls between neighbouring groups and turning a flat shell bed into a cratered landscape, each crater holding one territory and a cluster of shells. Researchers describe this digging as niche construction or ecosystem engineering. Where the bed is a continuous layer of shells with little sand, the fish are too small to move shells or build walls.

In a 3D-printed shell experiment, N. multifasciatus preferred shells that were fully intact and either enlarged, lengthened or had widened apertures. Wikipedia similarly notes that shells suitable for aquaria have a round opening and open coils.

Tank size, sand and shell count

• Footprint: Seriously Fish gives 45 x 30 x 30 cm (18 x 12 x 12 in), about 40 litres, as the minimum for a pair of either species. Floor area matters more than height, because territories sit on the bottom.
• Sand: a sandy substrate at least 5 cm (2 in) deep, with large open areas. Both species dig, and L. ocellatus habitually buries its shell and defends it.
• Shells: provide more shells than there are fish. In the wild, each N. multifasciatus territory holds at least as many shells as individuals, and each fish lives in its own shell. Colonial species may use hundreds of shells, whereas a brevis-group pair typically needs one.
• Territory size: an N. multifasciatus territory is usually no more than about 15 cm (6 in) across, so a tank floor can hold several neighbouring territories.

Tanganyika water chemistry

Lake Tanganyika is alkaline: Wikipedia gives a pH of about 9 from 0 to 100 m depth, falling to 8.3–8.5 in the deepest parts, and electrical conductivity of about 670–690 µS/cm. Surface temperature ranges from about 24 °C in the south in early August to 28–29 °C late in the rainy season, while deep water stays at 23.1–23.4 °C. Below about 150 m the water is anoxic and contains hydrogen sulfide.

Aquarium ranges are from Seriously Fish. Hard, alkaline water is listed as an essential requirement for shell dwellers. For buffering methods and mineral additives see the water-chemistry guides.

Colony behaviour

In the wild, N. multifasciatus lives in long-term groups of up to about 20 fish on fixed territories. A group consists of one dominant male, several adult females, subordinate males and juveniles. The dominant male secures most of the reproduction and uses his shell cluster to attract females from neighbouring territories, while subordinate males breed very little. Females divide the territory into sub-territories and defend several shells against rival females, especially while caring for young. Fish that try to join an established group, particularly males, meet intense aggression from residents. Dispersal is very limited, typically under 2 m, and within-group aggression drops sharply once home shells are more than 10–15 cm apart.

In aquaria, Seriously Fish reports that colonies form when the fish are kept with more shells than fish. Both species are territorial and defend their shell and the area around it vigorously; L. ocellatus males may also bury neighbouring shells to stop other fish moving in. Both are shell brooders: N. multifasciatus eggs hatch in about 24 hours, while L. ocellatus eggs hatch in about 3 days and the fry swim freely at about 10 days. Territoriality and reproductive strategies are covered in their own guides.

Tankmates and feeding

Seriously Fish lists small Tanganyikan rock dwellers such as Neolamprologus brichardi and smaller Julidochromis species, and open-water fish such as Cyprichromis, as compatible with both species. The rock dwellers use the rockwork while the shell dwellers keep to the sand, and open-water fish occupy the upper levels. Live and frozen foods should form the bulk of the diet, although dried foods are usually accepted.