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Ecology and Breeding Behavior of a Cichlid Fish, Cyrtocara Eucinostomus, on a Large Lek in Lake Malawi, Africa

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Ecology and Breeding Behavior of a Cichlid Fish, Cyrtocara Eucinostomus, on a Large Lek in Lake Malawi, Africa Env. Biol. Fish. Vol. 8, No. 2, pp. 81-96, 1983 Ecology and breeding behavior of a cichlid fish, Cyrtocara eucinostomus, on a large lek in Lake Malawi, Africa Kenneth Robert McKaye Duke University Marine Laboratory, Pivers Island, Beaufort, North Carolina 28516, U.S.A. Keywords: Arena, Mouthbrooding, Sociobiology, Predation, Cape Maclear, Zooplankton, Cormorant, Bagrus meridionalis Synopsis Cyrtocara eucinostomus, a mouthbrooding cichlid, breeds on a 4 km long breeding arena between 3-9 m depth in the Cape Maclear region of Lake Malawi. At times over 50,000 males display there, making this breeding arena the largest ever reported. The form and function of the arena and the behavior of the fish on the arena are analogous to bird leks. This arena serves only as a mating ground. All parental care is provided by the females, which leave the arena with the eggs. Courtship takes place in the morning and most of the males leave in the afternoon to forage on zooplankton in deeper water. They return at dusk. The few males that remain on the arena switch their behavior from courting to foraging on zooplankton. Comparisons of this fish arena are made with bird leks and it is concluded that the mating system of this fish can be defined as a lek in the avian sense. 1) There is no male parental care and an absence of monogamous pair bonding. 2) Males and females are sexually dimorphic and there are males present which mimic females to gain entrance into the arena. 3) The arena is traditional with a lack of environmental constraints and is away from the primary feeding grounds. In order to determine 1) if this arena could be considered a true lek and 2) what the factors are which account for the location of this remarkably large arena in shallow water, data were collected upon: 1) the depth distribution of C. eucinostomus; 2) distribution and size of the nests on the arena; 3) the behavior of the fish on the arena; 4) the feeding habits of C. eucinostomus; 5) the distribution of the zooplankton upon which C. eucinostomus feeds; 6) water temperature throughout the year; 7) response of males to cormorants; 8) depth distribution and stomach analysis of predatory catfish which feed on C. eucinostomus. Based on this natural history data, it is concluded that the occurrence of the arena in shallow water is probably due to C. eucinostomus avoiding deep dwelling catfish which feed at night upon them and other cichlids. Introduction McConnell 1969, Fryer & lies 1972, Baylis 1974, Barlow 1974, 1976, Brichard 1975, Balon 1977, Cichlid fishes exhibit a wide range of breeding M cKaye 1977, Keenleyside 1979, W itte 1981). The habits, varying from the biparental care of young latter reproductive mode is characteristic of most of for periods of over 2 months to uni-parental mouth­ the cichlid fishes of the Great Lakes of Africa. In brooding of young by either male or female (Lowe- Lake Malawi, the males of many of these cichlid species congregate on spawning arenas (Fryer & Received 4.8.1981 Accepted 16.4.1982 lies 1972) for the apparent purpose of attracting © 1983, Dr W. Junk Publishers, The Hague. Printed in The Netherlands. 0378-1909/83/0082-0081 /S03.20 81 and displaying to females. The eggs are both Malawi. The hypotheses to account for the selec­ fertilized in and retained in the female’s mouth and tion of this site by males of this species are: (1) it is a there is no male parental care of the young. The place where there is abundant food; (2) it has the females usually leave the arena, carrying their only suitable substrate; (3) competitors force them young for a while and release them elsewhere. Both into this area; (4) physical constraints, relating to the structure of the arena and the behavior of the temperature, oxygen or wave action make the site fish are considered analogous those seen in lekking atractive; 5) it is the area most secure from pre­ birds (Lack 1968, Fryer & lies 1972). dators. Lek-based mating systems are characterized by Data were collected on: (1) the depth distribution polygynous or promiscuous mating, weak or no of C. eucinostomus; (2) distribution and size of the pair-bonding, no paternal care and localized areas nests on the arena; (3) the behavior of the fish on where males and females congregate to mate (Se- the arena; (4) the feeding habits of C. eucinostomus; lander 1972, Wilson 1975). Males establish them­ (5) the distribution of the zooplankton upon which selves on the lek prior to mating (Beuchner 1961, C. eucinostomus feeds; (6) water temperature Snow 1963) and as a result of competition for throughout the year; (7) response of the males to females, a ritualized dominance hierarchy has usu­ cormorants; (8) the depth distribution and stomach ally evolved. Loiselle & Barlow (1979) consider that analysis of predatory catfish which feed upon C. ‘all the classic features of such avian leks may be eucinostomus. interpreted as manifestations of an hierarchical The natural history data presented here will be social structure’. used to discuss: (1) the extent to which this mating The evolution and adaptive value of lekking is system can be considered a lek, in the classical not well understood. Bird leks probably evolved ‘avian’ sense; (2) the factors which account for the from communal groupings (Crook 1965) where location of the remarkably large arena; (3) variation there existed competition for breeding sites as well in the form of the arenas in different areas in the as synchronous breeding (Selander 1972). Since leks lake. occur primarily in species inhabiting open country or having limited breeding areas (Loiselle & Barlow 1979), it is likely that they serve to concentrate Methods and materials widely distributed stocks of males and females. Loiselle & Barlow (1979) compare avian and fish Observations on the breeding behavior of C. eucino­ leks, and acknowledge some controversy exists over stomus were made underwater with open-circuit their use of the term ‘lek’ for many of the fish SCUBA from December 1977 to August 1980. breeding systems they discuss. To be considered a Counts, measures and general notes were made on ‘true’ lek, ornithologists require: (1) that the arena writing slates and transcribed after each dive. Indi­ serve only as a mating ground with the female vidual nest-holding males were observed for periods leaving to tend the young by herself and (2) the of 15 min at an average distance of 2-3 m, depend­ absence of habitat constraints in determining the ing on visibility. A total of thirty-four males were location or extent of the arena (Pitelka, in Loiselle watched between 0600 and 1300 h and nine dif­ & Barlow 1979). In Lake Malawi, Africa, the ferent males were observed from 1300 to 1900 h. breeding arenas of several cichlid species, including The number of foraging bites, mouthfuls of sand Lethrinops furcicauda, L. aurita and Cyrtocara moved to build nests, attacks and threats upon argyrosoma exhibit these classical characteristics of fishes and courting of females were recorded. Indi­ avian leks (personal observation). vidual egg-laying females were followed when over This report concerns the ecology and breeding the arena and the number of eggs laid and distance behavior of C. eucinostomus along a 4 km long, traveled throughout the lek were recorded. 3-12 m deep spawning arena off the Nankumba Peninsula in the Cape Maclear region of Lake 82 Abundance of C. eucinostomus and their nests: The the arena. The time an individual cormorant fished num ber o f C. eucinostomus and their nests were was recorded. The depth at which it fished was estimated by two divers counting the fish within 5 m determined from estimating the distance from the of the bottom and 2 m on either side of a 50 m shore and knowing the depth profile of the region. transect line laid along a depth contour (100 m2 of bottom surface for each diver). From November Collection o f C. eucinostomus for gonadal study and 1977 until July 1978 and in June and July 1979, at tagging: Both males and females were collected with least two 100 m2 surface transects were made each gill nets at various times on the breeding arena. The month at each 3 m depth interval, down to 32 m. gonads were examined and all the eggs were count­ The base diameter, top diameter and height of 15 C. ed. All of the eggs in the gonads of sixteen females eucinostomus nests (Fig. 1) were measured on 26 collected on 14-18 July 1980 were measured to the July, 1980 in Nkhata Bay (approximately 200 miles nearest 0.1 mm. The largest eggs of all fish were also north of the main study). On 29 July, 1980, 15 nests measured through a microscope, using an ocular were measured on the four kilometer arena. micrometer. Males were characterized as either ‘ripe,’ with large white testes, or 'non-ripe,' with Occupancy o f nests: During a 6 month period from small string-like testes. One hundred and twenty February-July 1978, the number of nests occupied males were tagged underwater with Dennison T and unoccupied were counted at various times tags and their standard lengths were measured. The throughout the day. The number of nests counted males were returned to their original nests after for each hour ranged between 104 and 444. If no tagging. male was seen attacking other males or building up the nest it was termed unoccupied. Counts were also Stomach analysis o f C. eucinostomus: Four collec­ made between 0700 and 1000 h when white-necked tions of C.
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