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October 17, 2014

Happy Friday! I thought that this week I would focus on just one genus of fish – the absolutely beautiful Nimbochromis of Lake Malawi. As a group, they are known as “sleeper” cichlids for their ambush style of hunting.

N. linni and N. venustus are found in the deeper regions of the lake. Nimbochromis linni spends its time in the deep rocky depths seeking juvenile cichlids hiding within the various crevices. When one is spotted, N. linni will lie down upon a rock with its mouth just above the crevice. Its brown mottled patterning helps it blend seamlessly with the sediment-glazed rocks and it will wait up to several minutes for its prey to come towards it. When in range, N. linni extends its highly protrusible mouth and suctions the juvenile cichlid from its hiding place. While resting or feeding, these fish are highly camouflaged, but when in breeding condition the male will take on beautiful deep blue coloration over his body, with borders of red, orange and yellow in his fins.

Nimbochromis linni

Nimbochromis venustus prefers open depths with sandy bottoms, devoid of the rocks favored by N. linni. Instead of resting itself upon rocks while awaiting its prey, when N. venustus spots a flock of juvenile cichlids, it ploughs its body into the sandy substrate and waits motionlessly for the fish to come within striking distance. It is thought that the adult coloration of pale yellow flanks with brown camouflage spots attracts young cichlids of many other species, drawing its prey near. Males are quite a bit brighter than females with bolder yellow coloration and brilliant blue cheeks. An especially bright yellow blaze runs from just above his lips to the start of his dorsal fin. Each of his fins is yellow and blue with bright white edges. When in breeding conditions, the spots of the males will be completely overlain with brilliant yellow, though in some populations they appear much bluer in the flanks – almost the color of Otopharynx lithobates “Yellow Blaze”.

Nimbochromis venustus

N. livingstoni and N. polystigma, on the other hand, prefer the shallows of the lake. Nimbochromis livingstoni occupies open, muddy areas of Lake Malawi. It has the most extreme “sleeper” tactics of any of the Nimbochromis – it will lay prone on its side, perhaps shuffling slightly into the sand or mud to obscure its outline, and waits for prey whilst ‘playing dead’ for up to three minutes. Its brown spots over a pale whitish body aid in breaking up the outline of the fish, not to mention white coloration is also an excellent attractant for young cichlids. When a curious juvenile approaches the interesting white object on the sand, N. livingstoni executes a quick sideways strike to catch its prey. Much like the other Nimbochromis species, breeding males attain a bright blue coloration over their body with a red anal fin and white-rimmed dorsal fin.

Nimbochromis livingstoni

Nimbochromis polystigma prefers a vegetated substrate in the wild and will often congregate in large groups of anywhere from 20 to 500 subadult to adult fish, cruising their habitat and consuming any small fish they come across. Their spotted and speckled pattern, resembling both the large blotches of N. livingstoni and the tiny spots of N. linni, functions as camouflage amongst the aquatic grasses while they swim singly. In a lone state, the fish will rest upon the substrate to ambush its prey, though it does not lie on its side as N. livingstoni nor will it bury itself like N. venustus. Breeding males take on a lovely light blue coloration with apple-red anal fins.Thank you for your time and I hope you learned a bit about these Kaligonos, or sleeper predators, of Lake Malawi.

Nimbochromis polystigma

Jessica Supalla