Melanochromis robustus Johnson 1985

Konings, Adrianus F. & Stauffer, Jay R., 2012, Review of the Lake Malaŵi genus Melanochromis (Teleostei: Cichlidae) with a description of a new species, Zootaxa 3258, pp. 1-27 : 4-7

Melanochromis robustus Johnson 1985

( Fig. 2 ; Table 1 )

Melanochromis cf. brevis (non Trewavas) Ribbink et al. 1983 Melanochromis brevis (non Trewavas) Konings 1995

Material examined. AMNH 35386, holotype, male, 124.2 mm SL, Malaŵi: Lake Malaŵi: “Chizimulu Island”, Davies et al.; PSU 8090, 6, 101.3–124.0 mm SL, Malaŵi: Lake Malaŵi: Chinyankwazi Island: 13° 50.3’S, 34° 57.4’E, A. Konings, 11 Oct 2009; PSU 10565, 1, 125.8 mm SL, Malaŵi: Lake Malaŵi: Chinyankwazi Island: 13° 50.3’S, 34° 57.4’E, J. Stauffer & A. Konings, 9 Feb. 2003; PSU 8091, 3, 87.0– 95.1 mm SL, Malaŵi: Lake Malaŵi: Mumbo Island: 13° 59.1’S, 34° 45.3’E, J. Stauffer & A. Konings, 8 Feb 2003.

Diagnosis. Melanochromis robustus has a basic melanin pattern consisting of two longitudinal black stripes on the body, of which the mid-lateral stripe reverses colour with the background in the breeding male—a character that makes it a member of Melanochromis . Female M. robustus are distinguished from all other congeners, except those of M. melanopterus , M. vermivorus , and M. mpoto , by a gray to brown coloured body (white to yellow in other congeners). Mouthbrooding females may have additional vertical bars on the flanks, but these are more diffuse than the horizontal stripes. Both male and female M. robustus are distinguished from M. melanopterus , M. vermivorus , and M. mpoto by a broader interorbital breadth, the width of which is 26.1–29.6 % of HL (16.6–20.6 % in M. melanopterus , 18.5–25.5 % in M. vermivorus , and 14.8–21.8 % HL in M. mpoto n. sp.). Male M. robustus in breeding colouration are distinguished from all other congeners by a dark-blue body colour and two light blue horizontal stripes on the flank superimposed with dark-blue to black vertical bars. The bars are interrupted by the light-coloured horizontal lines. None of the other known species of Melanochromis has a male colouration where the horizontal and vertical elements of the pattern are expressed simultaneously. Superficially, breeding males of the sympatric and smaller M. heterochromis have a similar colouration (albeit lacking the vertical bars). Melanochromis heterochromis can also be distinguished by its light-coloured mid-lateral stripe, which rarely spans more than two scales but is usually three to four scales deep in M. robustus . Melanochromis robustus is further distinguished from M. heterochromis by a longer snout, 33.8–38.0 % HL vs. 26.8–31.5 % in M. heterochromis , and by a deeper caudal peduncle, 12.9–14.4 % SL vs. 9.8–11.7 % in M. heterochromis .

Description. Morphometric ratios and meristic values as shown in Table 1 . Medium-sized to large mbuna, ovoid body (mean BD 37.3% SL) with greatest depth at about second to fourth dorsal spine. Dorsal body profile with gradual curve downward, more acute towards the caudal peduncle; ventral body profile slightly convex between pelvic fins and base of rays of anal fin with upward taper to caudal peduncle. Dorsal head profile rounded, with continuous curve between interorbital and dorsal-fin origin; horizontal eye diameter (mean 27.3% HL) greater than preorbital depth; majority of eye (along horizontal axis) positioned in anterior half of head; snout straight to slightly concave in some individuals; jaws isognathous; tooth bands with 3–5 rows in lower and upper jaws; teeth in anterior outer row unequally bicuspid with lateral teeth primarily unicuspid, and teeth in inner rows unicuspid (some teeth shouldered); at junction of outer and innermost row teeth as single series of small unicuspids.

Dorsal fin with XVI–XVIII (mode XVII) spines and 8–10 (mode 9) soft rays. Anal fin with III spines and 6 to 8 (mode 7) soft rays. First 3 or 4 dorsal spines becoming gradually longer posteriorly with fourth spine about 1.5 times length of first; last 13 spines becoming slightly longer posteriorly with last spine longest, about three times length of first; soft dorsal with rounded (females) or rounded to subacuminate (males) tip, third or fourth ray longest, reaching approximately base of caudal fin in females and approximately ¼ length of caudal in males. Anal spines progressively increasing in length posteriorly; third or fourth ray longest, reaching base of caudal fin; 1–3 small yellow spots on posterior anal fin in females and 2–10 yellow spots on posterior anal fin in males. Caudal fin subtruncate to emarginate. Pelvic fin not reaching anal fin in females, but extending to second or third spine of anal fin in large males. Pectoral fin short and paddle-shaped, reaching superimposed vertical line through base of 10th or 11th dorsal spine.

Flank scales large, ctenoid with abrupt transition to small scales on breast; cheek with 3–5 (mean 4) rows of small scales; caudal fin with tiny scales to margin; no scales on other fins.

Colouration. Breeding males: head below eye dark blue/black with light-blue interorbital band, nape and postorbital part of head light blue to gray. Body blue/dark blue with solid light-blue midlateral stripe and less welldefined light-blue dorso-lateral stripe; anteriormost 2–5 vertical bars darker and superimposed on pattern of horizontal stripes; vertical bars interrupted where intersecting light-blue horizontal stripes; caudal peduncle dark blue/ gray with light-blue midlateral stripe extending onto caudal fin; belly and breast dark blue/black. Dorsal fin light blue with black submarginal band, in some males submarginal band not solid, and light-blue lappets. Caudal fin with dark-blue/black membranes, clear posterior margin, and light-blue rays. Anal fin blue with broad black submarginal band, light-blue anterior margin, and 2–10 small orange/yellow ocelli on posterior part of soft-rayed portion. Pelvic fin black with light-blue anterior margin. Pectoral fin with dark-gray/black rays and clear membranes. Females: head gray/green with green iridescent spots on post-orbital part and black opercular spot; dark interorbital bar with some green iridescent spots; short, dark horizontal stripe behind eye not extending to opercular spot. Body gray/green-yellow with solid black midlateral stripe extending to but not onto caudal peduncle, and interrupted black dorso-lateral stripe; faint dark vertical bars over horizontal stripes, more conspicuous in mouthbrooding females. Dorsal and anal fin gray with faint black submarginal band. Caudal fin with black spot at base; membranes light gray with dark submarginal band and outer margin clear; rays light-blue/white. Pelvic fin gray with narrow white/light-blue anterior margin. Pectoral fin clear with gray rays.

Distribution and field observations. Melanochromis robustus is uncommon in occurrence in the very shallow (<5 m deep) rocky habitat at the islands of Chinyankwazi and Mumbo ( Fig. 1). Ribbink et al. (1983) report the presence of this species (as Melanochromis cf. brevis ) at other locations in the southeastern arm of the lake but we have not been able to confirm this.

Males in breeding colouration energetically defend spawning sites, which are located inside caves and crevices between the rocks, against conspecific males. Male territories have an estimated diameter of 2–3 meters. Territorial aggression against males of M. heterochromis , which is much more common at both islands, was not obvious, although the two species are sometimes difficult to tell apart on the basis of colouration, were it not for the much larger size of M. robustus . Females are rarely seen, and those that were have always been solitary; mouthbrooding females remain solitary and stay close to the rocky substrate. Ribbink et al. (1983) mention that stomach analyses of M. robustus revealed plankton and algae, and occasionally terrestrial insects such as ants and flies. The individuals we observed at the islands of Chinyankwazi and Mumbo suggest an opportunistic feeding behaviour in which the species is attracted to visible particles floating in the water column rather than collecting food by systematically browsing from the rocky substrate. Stomach analyses were not performed.

Figures

FIGURE 2. A. Melanochromis robustus, holotype, AMNH 35386, 124.2 mm SL, MalaŴi: Lake MalaŴi: “ Chizimulu Island ”, Davies et al., because of damage on left side of specimen shown from right side; B. M. robustus, male in breeding colouration (approx. 110 mm SL) at Chinyankwazi Island, Lake MalaŴi, MalaŴi; C. M. robustus, female (approx. 100 mm SL) at same locality as male.

Tables

TABLE 1. Morphometric and meristic data for Melanochromis robustus from Mumbo Island, Malaŵi (n = 3), from Chinyankwazi Island, Malaŵi (n = 7), and for the holotype (“ Chizimulu Island ”). Mean values as well as the ranges for these localities do not include those of the holotype because of it being grossly disproportionate.

Melanochromis robustus	mean	holotype	Mumbo range	Chinyankwazi range
Standard length, mm Head length, mm	104.0 34.1	124.2 40.8	87.0–95.1 28.9–31.2	101.3–124.0 32.0–40.2
% standard length
Head length Body depth Snout to dorsal Snout to pelvic Dorsal-fin base length	32.8 37.3 35.0 38.8 61.6	32.8 38.5 33.1 45.2 57.3	32.7–34.7 36.5–36.6 34.7–36.5 38.9–39.3 60.8–62.2	31.0–34.1 34.7–40.2 34.0–35.7 37.5–40.2 60.7–62.3 ......continue on next page