MELANOCHROMIS CRABRO SP. NOV.: A CICHLID FISH FROM LAKE MALAWI WHICH FEEDS ON ECTOPARASITES AND CATFISH EGGS

by

A. J. RIBBINK1 and D. S. C. LEWIS2 (1: J. L. B. Smith Institute of Ichthyology,Grahamstown, South Africa ; 2: FisheriesResearch Station, MonkeyBay, Malawi)

SUMMARY

Melanochromiscrabro sp. nov., a member of the "Mbuna" group, is described from Lake Malawi. It feeds upon a variety of foods, but appears to be adapted to feed on Argulus africanus,a branchiuran parasite commonly found on the catfish, Bagrusmeridionalis. It is suggested that the host-cleaner association also facilitates an egg-stealing habit, since M. crabrorobs B. meridionalisof its eggs which are laid on the substratum.

INTRODUCTION

The endemic rock frequenting cichlids of Lake Malawi display a re- markable degree of adaptive radiation and utilize a wide variety of food resources (FRYER, 1959; FRYER & ILES, 1972). These include various components of the conglomerate of algae and invertebrates (Aufwuchs) which forms a mat over the rock surfaces, phytoplankton, zooplankton, insect larvae and nymphs, scales and fins of other fishes, molluscs, and eggs and juveniles of other cichlids. Recent field studies have brought to light two more dietary components which have not previously been recorded in fishes from Lake Malawi. An undescribed species has been found to feed upon branchiuran parasites of the large siluroid Bagrus meridionalis Gunther and to eat the eggs of its host. In this paper the fish is formally described and an account is given of its diet, habits and distribution.

SPECIES DESCRIPTION Melanochromis crabro sp. nov. (fig. 1 )

Synonymy and Generic Status

Although never formally described this species has been well known in the aquarium trade for some time where it has been referred to as ""Pseudotropheus chamaeleo". 73

"Pseudotropheus chamaeleo" Staeck, 1977. "Pseudotropheus chamaeleo" Mayland, 1978. The taxonomy of the Mbuna group of cichlids is very confused and until it has been revised it is probably best to follow the generic diag- noses laid down by TREWAVAS (1935). Trewavas separates the genera Pseudotropheus and Melanochromis on pharyngeal dentition, Pseudotropheus having "Pharyngeal teeth very small, densely crowded posteriorly" and Melanochromis having "Pharyngeal teeth neither very numerous nor den- sely crowded". The pharyngeal dentition of M. crabro conforms to the second diagnosis and therefore, for the time being, it is placed in the genus Melanochromis.

Fig. 1. Melanochromiscrabro-holotype. Female of 66.0 mm standard length (80 mm total length) (Scale = 10 mm).

Etymology

"Crabro" is the Latin name for "hornet". This refers to the distinctive yellow and brown colour pattern which is reminiscent of the European hornet.

Description

Based on the holotype (a female, 66.0 mm standard length; deposited in BMNH and ten paratypes (5 females 57.8, 61.0, 62.7, 70.6 and 76.8 mm standard length and 5 males 48.4, 50.0, 53.0, 53.4 and 64.7 mm stan- dard length, deposited in BMNH). All of these were caught at Maleri Island ( 13°53' S, 34°37' E) at a depth of 15-18 m over a rocky substrate