Environmental Biology of Fishes 59: 111–115, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. Aggressive mimicry in the intra-populational color variation of the Tanganyikan scale-eater Perissodus microlepis (Cichlidae) Michio Hori a & Katsutoshi Watanabe b,c a Department of Zoology, Faculty of Science, Kyoto University, Kyoto 606-8502, Japan (e-mail: hori@terra.zool.kyoto-u.ac.jp) b Corresponding author: Department of Marine Bioscience, Fukui Prefectural University, Gakuen-cho 1-1, Obama, Fukui 917-0003, Japan c Present address: Department of Molecular Biology of Marine Organisms, Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164-8639, Japan (e-mail: watanak@ori.u-tokyo.ac.jp) Received 20 August 1999 Accepted 6 February 2000 Key words: Cyprichromis leptosoma, Paracyprichromis nigripinnis, exploitative mutualism Synopsis A color morph of the Tanganyikan scale-eater, Perissodus microlepis (Cichlidae), considered to be an example of aggressive mimicry, is reported from the rocky littoral area at the southern end of Lake Tanganyika, Zambia. The anal fin of the morph is yellow, instead of the usual dark or transparent, being closely similar to that of the gregarious cyprichrominine cichlids, Cyprichromis leptosoma species complex and Paracyprichromis nigripinnis, abundant in the area. The color morph of Perissodus microlepis was observed to mingle with and attack shoals of the prey. About 24% of P. microlepis observed in less than 15 m depth at Kasenga Point were the yellow-fin type. The color variation, which is likely associated with a variation in feeding mode within this population, probably evolved and has been maintained by the local community structure, which included abundant cyprichrominine fishes. Introduction The cichlids of the African Great Lakes have a great diversity of feeding habits (Fryer 1959, Hori 1983, 1987). Amongst the latter, scale-eating is one of the most unusual, some independently-evolved lin- eages of lepidophages having been reported from Lake Tanganyika, Lake Malawi and Lake Victoria (Fryer & Iles 1972). Lepidophagous species are rather widely distributed in fishes, being known in at least eleven families, including both marine and freshwater (Gerking 1994). It has been inferred that scale-eaters evolved from both herbivorous and carnivorous ances- tors (Fryer et al. 1955, Liem & Stewart 1976), the origin of scale-eating, degree of trophic dependence on scales and associated behavioral features being thought to be linked to both the local community structure and intra- specific social relationships (Sazima 1983, Hori 1987). Perissodus microlepis is one of the most com- mon scale-eaters in Lake Tanganyika (Poll 1986, Brichard 1989). The feeding ecology and behavior of the species have been observed in the rocky lit- toral area at the northern end of the lake, and sev- eral hunting techniques, such as stealthy approach and ambush have been reported (Nshombo 1994a,b, Nshombo et al. 1985). Nshombo (1994b) has reported that this species possesses pale-dark dichromatism related to the hunting techniques. At the southern part of Lake Tanganyika, we have found a distinct color morph of P. microlepis, which can be characterized by a yellow anal fin instead of the commonly recorded dark or transparent condition. The former color morph seems to mimic similarly- colored shoaling cichlids, thus being able to mingle with and attack the latter. In this paper, we report this intra-populational color variation of P. microlepis as an