Weird and Wonderful Tanganyika Cichlids
Lake Tanganyika is home to a wide range of different cichlids; most of them endemic to the lake. When studying and keeping Lake Tanganyika, it is hard not to be amazed by the rich variation that these species exhibit. Some are huge, others are tiny, some are extremely colourful, others are so well camouflaged that they are easy to miss even in the aquarium, and some are skilled attack predators, while others spend their days slowly and meticulously filtering sand through their gills in search of tiny crustaceans.
The biggest known Tanganyika cichlid can reach a length of 90 cm, while the smallest one stays at a mere 4 cm. The name of this huge cichlid is Boulengerochromis microlepis and it spends its life cruising the pelagic in search of suitable prey. Being large means that you can overpower and swallow even big fish and this is probably why Boulengerochromis microlepis has grown so immense. It may also be a result of sexual preferences during breeding. Boulengerochromis microlepis can weigh up to about 3 kg and is a fairly unknown cichlid. It is naturally difficult to keep in aquariums due to its large size and pelagic life-style.
The smallest known Tanganyika cichlid is Neolamprologus multifasciatus, a tiny shell-dwelling fish that you can find on the sandy bottom of the lake. Its minute size is an adaptation to a shell-dwelling lifestyle. Neolamprologus multifasciatus will seek out empty shells that are scattered over the bottom and scoop sand from below one of them until it sinks down below the sandy surface. By flickering sand over the shell, the fish makes it more or less invisible from above. A tiny entrance is opened up, and the shell will then serve as both hiding space and spawning site for Neolamprologus multifasciatus. If the fish were any bigger, the selection of suitable shells would be much smaller.
Adapt to your habitat
If you are interested in the various specializations exhibited by Tanganyika cichlids, you should definitely take a closer look at Eretmodus cyanostictus, a fascinating goby cichlid living in the turbulent shallows of Lake Tanganyika. This habitat is exposed to forceful waves and surges and Eretmodus cyanostictus must therefore stay within close contact with the bottom in order to survive. A normal swim bladder is not very useful in this situation the swim bladder of Eretmodus cyanostictus has therefore decreased into a much reduced variant. Other adaptations that make it easier for Eretmodus cyanostictus to live in the shallows can be seen in the compressed body shape as well as in the specialized dentition and ventral fins.
Triglachromis otostigma lives in muddy bottom regions of Lake Tanganyika and has therefore developed a set of pectoral fins with bendable fin tips. Watching this fish feed is really amusing, because it will actually swim backwards. By swimming backwards, Triglachromis otostigma can use its pectoral fins to unearth insect larvae hiding in the mud.
Adapt to your food
In Lake Tanganyika, several different species in the genus Perissodus has adapted to a life as scale-rippers. Instead of devouring whole prey, they settle for the shells of a living fish. A problem is of course that ripping the scales from a fish can be quite complicated. Many Perissodus species have therefore evolved specialized heads and jaws that are skewed to one side in order to make scale-ripping less of an arduous task.
Another fascination adaptation that facilitates feeding can bee seen in Benthochromis tricoti. This fish exhibit a protruding mouth that can be stretched out and function as a sucking tube. This adaptation makes it possible for Benthochromis tricoti to suck in tiny shrimps, copepods and plankton. This feeding system is highly effective, because despite feeding exclusively on infinitesimal food types, Benthochromis tricoti can grow up to 20 cm in length.
Last, but certainly not least, we must naturally mentioned the enthralling Petrochromis fasciolatus when talking about interesting feeding adaptations. This species feeds exclusively from the underside of rocks, and has therefore developed a mouth that opens in an upward fashion. This feature distinguishes it from most other cichlid species, since the normal configuration is to have a mouth that projects downwards.
Pro’s and con’s of specialization
In most cases, anatomical specialization comes with a price, and a bodily feature that is great for certain things can simultaneously cause trouble in other situations. Take for instance Altolamprologus compressiceps, a cichlid species fully adapted to a life feeding on freshwater shrimp and cichlid fry from rock dwelling cichlid species. This fish has developed a really slim body shape that allows it to squeeze itself into rock crevices where it can find plenty of food. While this high-backed and laterally compressed body is great reaching into nocks and crannies, it poses a problem when highly aggressive cichlid parents try to protect their offspring, since it makes it really difficult for Altolamprologus compressiceps to quickly retreat or otherwise fend of attackers. Throughout the course of evolution, Altolamprologus compressiceps has solved this problem by developing yet another adaptation – extremely thick and strong scales that will function as armour and protect it from vicious cichlid attacks.
Species from the genus Trematocara spend the nights searching for small invertebrates in the dark, and has therefore developed intricate lateral line system that allows them to locate food without having to rely on eye-sight. By staying away from desirable foraging areas during the day, and even during dusk and dawn, they avoid having to compete with the many other species interested in the same food types.
Chose your battles
Adapting to a new way of life is one way of dealing with fierce competition. An example of this can be seen in Neolamprologus toae and Neolamprologus sexfasciatus, two closely related species that inhabit the same part of Lake Tanganyika. Both species feed at night, and in the same area, but while Neolamprologus toae feed chiefly on insect larvae, Neolamprologus sexfasciatus sticks to a menu of molluscs. Scientists believe that Neolamprologus sexfasciatus was unable to compete with Neolamprologus toae over the desirable insect larvae and therefore retorted to feeding on molluscs that were rejected by the other species.
Coping with pressure
An animal that develops a way of coping with dramatic changes in water pressure is truly blessed, because this ability will make it possible for it to take advantage of multiple feeding niches. One example this ability is to be found among the cichlids in the genus Trematocara; mesmerizing benthic invertebrate feeders that can stay close to the surface as well as dive down to depths exceeding 300 meters. During the day, the Trematocaras will stay down at these great depths where no other cichlids dare to venture and feed alone without any competition. As the sun sets and the day active species seek shelter, you can see the Trematocaras swimming up towards the surface and feed at depths located no further down than a few meters. The Trematocara cichlids are not only the deepest living cichlids in Lake Tanganyika; they are the deepest living cichlids in the entire world.
Specialized breeding behaviour in Tanganyika cichlids
The cichlids in Lake Tanganyika exhibit a wide range of attention-grabbing breeding specializations and many of them are quite easy to coax into spawning in the aquarium, as long as you know what they need to spawn. Breeding Tanganyika cichlids is highly rewarding since it gives you a chance to study these interesting behaviours from the comfort of your own home. Extensive parental care is for instance very common in Tanganyika cichlids and watching them raise their young in the aquarium is a true delight.
Earlier in this article, we mentioned a species that utilizes abandoned shells as spawning sites, the miniscule 4 cm long Neolamprologus multifasciatus. Finding shells suitable for a 4 cm long fish it not very difficult, but what would you do if you were a 15 cm long cichlid in need of a suitable shell to spawn in? This is the problem faced by the pack hunting carnivore cichlid named Lamprologus callipterus, a species where the male fish can exceed 15 cm in length as an adult. Being large is naturally a positive thing when you and your pack members work together to dismember big prey, but it does cause problems during spawning. In order to combat this predicament, the two sexes grow into very different sizes. The female stays around a mere 5 cm in length and can therefore easily fit into a shell. The male will focus on defending the territory and collect a large compilation of suitable shells from which the female can have her pick. The shells are placed inside pits which can reach 1 meter across. A successful male that manages to collect a lot of attractive shells can have several females breeding within his territory.
Substrate spawning, such as in the example above, is very common in Tanganyika cichlids. The mud-dwelling Triglachromis otostigma discussed earlier will for instance use those specialized pectoral fins not only to feed, but to dig a long tunnel-shaped cave where the offspring will be safe. Not all Tanganyika cichlids are substrate spawners however. There are for instance the sardine-like members of the genus Cyprichromis, a schooling type of fish that spawns out in the open water. Cyprichromis species form huge groups that can consist of many thousand individuals and when the males release their sperm simultaneously, the water around them will be literary clouded with semen. The females position themselves head-down before releasing their eggs, and will then immediately swim down and catch the eggs as they fall. The eggs are carefully carried in the mouth of the mother fish and fertilized by the sperm-cloud. After hatching, the offspring will stay inside the mouth of their mother for approximately 3 more weeks. The fry are not released until they have grown big enough to be more or less independent and able to form their own school. This adaptation in Cyprichromis species means that they never have to waste energy competing with other fish over suitable spawning sites – they can spawn anywhere.
Carrying around the eggs inside the mouth of the female, so called maternal mouth-brooding, is very common among Tanganyika cichlids and the males have adapted in various ways to fit this behaviour. If you take a closer look at the delicate elongated ventral fins sported by the males of the Opthalmotilapia genus, you will for instance notice that the ends of these fins have small lobes attached to them. These lobes look very similar to the eggs produced by female Opthalmotilapia cichlids and will in a very peculiar manner increase the chances of fathering offspring for the male who exhibits them. Since this is a maternal mouth-brooding species, the female will pick up the eggs with her mouth directly after releasing them. The male will then place his “eggs” at the spawning site and wait for her to try to pick them up as well. When the female reaches for the eggs, the male will shoot out a mouthful of sperm and fertilize all the eggs inside her mouth. Due to the long and delicate ventral fins displayed by the males of this genus, Opthalmotilapia cichlids are commonly referred to as “featherfins”.
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