Serranochromis alvum, Stauffer & Bills & Skelton, 2021

Stauffer, Jay R., Bills, Roger & Skelton, Paul H., 2021, Four new species of Serranochromis (Teleostei: Cichlidae) from the Cuanza and Okavango river systems in Angola, including a preliminary key for the genus, Zootaxa 4908 (1), pp. 66-84 : 69-72

Serranochromis alvum new species

Suggested common name: Blue-Headed Largemouth Bream

( Fig. 2 ).

Holotype. SAIAB 186842, 151.8 mm SL (male), collected from Cuito-Cuanavale bridge, Cuito River, Okavango River system, Angola; 15º10’16.4” S, 19º11’39.3” E. Collected by R. Bills, P. H. Skelton, F. de Almedia, 18 May 2012. Collected with gill and seine nets.

Paratypes. SAIAB 205219 (5), 71.5–114.5 mm SL, data as for holotype .

Diagnosis. The presence of ocelli throughout the anal fin of breeding males distinguishes S. alvum from S. robustus and Serranochromis jallae (Boulenger) in which the ocelli in breeding males are restricted to the posterior 4–5 membranes of the anal fin. The exposed teeth of S. alvum differs from those of S. stappersi and S. altus , which possess small teeth that are buried in the lips. Serranochromis alvum has an emarginate caudal fin, while S. macrocephalus , S. janus (Trewavas) , and S. angusticeps have rounded caudal fins. The shorter jaw of S. alvum (43.4–53.5 % HL) separates it from Serranochromis spei (Trewavas) (53.5–57.2 % HL). Serranochromis alvum has 34–36 lateral-line scales, while S. thumbergi possesses greater than 39 lateral-line scales. The acute angle of the cleft of the mouth (50–60º of horizontal) of S. meridianus delimits it from the 30º angle of S. alvum . The long dark pectoral fins which reach past the middle of the dorsal fin separates S. longimanus from S. alvum . The interorbital width (14.3–15.9 % HL) of S. alvum is narrower than that of Serranochromis swartzi n. sp. (17.6–19.8), Serranochromis cuanza n. sp. (16.3–18.0), and Serranochromis cacuchi n. sp. (20.0–21.7).

Description. Morphometric ratios and meristic data in Table 1. Body shape and pigment patterns in Fig 2 .

Body slender, fusiform, and compressed, deepest at origin of dorsal fin. Dorsal-fin origin at vertical through posterior edge of operculum, dorsal-fin spines to maximum length over 5–6 spines, spine lappets prominent. Soft dorsal rounded behind, extending to base of caudal fin. Caudal peduncle short (13–18 % SL) 7.5 times in SL, slightly longer than deep (CPL/CPD 1.1–1.2). Caudal fin broad, relatively short (little more than half the head length), rectangular and truncate. Anal-fin origin closer to caudal-fin base than tip of snout, below vertical through first dorsal soft-ray; soft-rayed section with bluntly rounded hind edge, extending to caudal-fin base. Pectoral fin close behind gill slit, ventral on flanks, base sub-vertical, short, not extending beyond pelvic fins, postero-ventral margin bluntly rounded. Pelvic fins ventral, origin narrowly behind base of pectoral fin, short, not reaching origin to the anal fin, strong leading spine 2/3 length of fin. Scales small, in 15 even rows across flanks from dorsal-fin origin to anal-fin origin, 16 rows of scales around caudal peduncle, 34–36 in lateral line; upper lateral line gently curved, lower lateral line straight through mid-caudal peduncle; five scale rows between anterior dorsal and lateral line, two scale rows between soft dorsal and posterior end of upper lateral line, nape and chest scales reduced.

Head elongate 2.5–2.7 times in SL (37–39%SL), length greater than body depth, pointed with straight predorsal profile extending 20˚ above horizontal. Eyes large (HED 21–26.7%HL; VED 21.2–25.7% HL), dorso-lateral in anterior half of head, entirely above level of the mouth and before the dorsal edge of the operculum. Interorbit narrow, less than half orbit diameter. Snout relatively long, greater than orbit diameter, nares in mid-snout before orbits. Lachrymal (pre-orbit) depth equal to orbit diameter. Cheek below and behind orbits deep with 7–10 rows of scales. Post orbit half-length of head, interorbit 14.3–5.9% HL. Mouth terminal, large, protrusible; angle of closed jaw of holotype 30˚ below horizontal, posterior premaxilla to below anterior orbit, lips well developed, even. Teeth canini-form, exposed, widely spaced in 2 series on upper and lower jaws. First branchial arch with 3–4-1-9–11 gill-rakers. Gill-slit large, extending from upper flank opposite dorsal orbit rim in smooth arch to mid-ventral below orbits.

Coloration. Preserved specimens yellowish-brown with darker greyish brown interorbital and body bars, ventral surfaces yellow-brown. Fins light yellowish with grey markings; head with broad greyish band across lachrymal through eye to upper operculum and opercular spot. Body with two lateral black pigment bands and six broad dark brown bars to caudal-fin base reaching from dorsal fin to lower flanks, dark brown spots at base of scales. Live males with broad black bar from lachrymal through lower eye across post-orbit to large opercular spot; iridescent pale blue and white patches on cheeks and above post-orbital bar, white lower cheeks and gular, opercle dusted with grey and black below dorsal black bar, pale blue opercular membrane. Body bluish-black above, prominent black bars on body with white infused with blue interspaces between bars, below pectoral fins, and on lower flanks and ventral side. Dorsal fin with grey-black blotched membranes between anterior spines; dark grey to black blotches with light blocks on membranes between posterior 5–6 spines; soft dorsal with dark grey-black blotches and clear spots on membranes, edges grey. Caudal fin with elongate dark grey-black rectangles and white spots on membranes, a lighter creamish brown submarginal band and greyish black marginal band. Anal fin with 3– 4 rows of deep greyish-red spots between pale yellow bands. Pectoral fins with grey rays and translucent hyaline membranes. Pelvic fins with clear rays and a sooty dust over rays.

Habitat. Collected in gill nets set along the fringing Phragmites reed bed in the main Cuito channel at the Cuito-Cuanavale main road bridge ( Fig. 3 ). Water depths were approximately 1.5– 2m. The riverbed was mostly sand substrate with occasional marginal aquatic weed beds and fringing emergent beds of Phragmites .

Distribution. Currently known only from the type locality at Cuito-Cuanavale at the junction of the Cuito and Cuanavale rivers, tributary to the Okavango River in Angola.

Etymology. The specific name, alvum , a noun in apposition, is derived from the Latin, which means blotches and refers to the prominent lateral pigmentation.

Figures

FIGURE 2. Serranochromis alvum, Holotype SAIAB 186842, 151.8 mm SL, collected from Cuito Canavale bridge, Angola; 15º10’16.4”S 19º11’39.3”E, 18 May 2012.

FIGURE 3. The main Cuito channel at the Cuito-Cuanavale main road bridge, where Serranochromis alvum was collected.