With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Doctor Zhivago's antagonist is a physician.
text_B: Tropheus is a small genus of six species of cichlids endemic to Lake Tanganyika in East Africa .. genus. genus. species. species. cichlids. cichlids. endemic. endemism. Lake Tanganyika. Lake Tanganyika. East Africa. East Africa. The genus is widespread across all regions of Lake Tanganyika , from Burundi in the north to Zambia in the south .. genus. genus. Lake Tanganyika. Lake Tanganyika. Males and females are relatively similar , but do display obvious sexual dimorphism .. sexual dimorphism. sexual dimorphism. Males attain a somewhat larger size .. All species maternally mouthbrood their eggs and fry , and this characteristic provides their Latin name .. species. species. mouthbrood. mouthbrooding. Latin. Latin. Tropheus comes from the Greek trophos , which means `` to nurture '' .. trophos. trophos. The genus is fished lightly by the local population , but has never become a staple food fish due to its relatively small size and its habitat , which enables it to dart between rocks when threatened .. genus. genus. Most species occur along the coastal fringes of the lake at depths less than 3 m .. species. species. These rocky shores , with numerous rocky outcroppings and boulder formations , form a habitat similar to many of the mbuna cichlids of Lake Malawi .. cichlids. cichlids. mbuna. mbuna. This habitat provides shelter , and due to the shallow depth and the long hours of strong sunlight , heavy algal growth on which they feed .. The only Tropheus species to dwell further out and deeper in the lake is Tropheus duboisi , which in general inhabits deeper regions of the lake down to around 15-20 m. All species are algal grazers and have underslung mouths adapted to rasping algae and microinvertebrates from submerged rocks .. species. species. algae. algae. The genus is popular with aquarium hobbyists due to the beautiful markings and interesting behaviour .. genus. genus. Tropheus moorii in particular has become something of a cult fish within the hobby and many keepers have specialised in keeping nothing else .
not_related.