Study on diversity of fish communities in Lake Tangenyika

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Our field studies in the last decade have revealed that cooperative interspecific relationships as well as competitivc ones are highly incorporated in coastal fish communities in Lake Tanganyika. The great diversity of the fish communities are attributed to the explosive radiation of cichlids descended from several old lineages.In this project, we carried out the field studies at the sourthern water in Zambia and at the northern water in Burundi and mainly concerned with (1) comparison of fish communities in separated localities along the Zambian shoreline, (2) habitat utilization, reproductive behavior, mating systems, feeding bchaviour, and inter- and intraspecific interactions in cichlid fishes, and (3) taxonomic re-examination of cichlid fishes.For the first subject, we conducted line censuses at more than 10 localities and collected specimens. Main results we obtained were as follows : (a) geographic variations in morphology and coloration were greater in rock-dwellers than sand-d … More wellers, (b) it was suggested that two long sand beaches (7 and 13 km long) which have existed from ancient times (at least from 30 thousand years ago) functioned as barriers against genetic flow, and (c) some equivalent feeding niches, especially those of benthos-feeders, in fish communities were occupied by related but different species, and charcter displacement was found in some benthos-feeders. Furthermore, fish communities on the deep bottom (60-160 m deep) were explored by using gillnets. They consisted exclusively of carnivorous fishes such as zooplankton-feeders, benthos-feeders, piscivores and scaleeaters.On the second subject, we obtained many results. The most outstanding was the phenotypic plasticity in facultative shell-brooders. In populations that use empty gastropod shells as spawning substrate, only females or both males and females dwarfed compared with populations that use rock holes and crevices. Some shell-brooding populations of Lamprologus callipterus and Lepidiolamprologus attenuatus exhibited nearly the greatest sexual size dimorphism (male>>female)in the animal kingdom.For the third subject, specimens we collected in Burundi and Zambia waters were examined and compared with type specimens deposited in the British Museum etc.. Taxonomic reviews on some groups (i.c., the genus Xenotilapia) will be completed in near future. And, DNA analyzes for establishing a phylogenic tree of cichlid fishes are in progress. Less