Serranochromis robustus ( Günther 1864 )

Stauffer, Jay R., Bills, Roger, Skelton, Paul H. & Weyl, Olaf L. F., 2020, Re-elevation to species level and redescription of Serranochromis jallae and Serranochromis robustus (Teleostei: Cichlidae), Zootaxa 4858 (1), pp. 126-134 : 127-128

Serranochromis robustus ( Günther 1864)

Hemichromis robustus Günther 1864

Paratilapia robusta (in part) Boulenger 1899

Paratilapia thumbergi (in part) Boulenger 1911

Serranochromis robustus Jackson 1961

Misidentified as Serranochromis thumbergi Regan 1922 , Trewavas 1935, Bertram et al. 1942, Lowe 1952.

Although we have not examined specimens of Pelmatochromis tanganyicae Bordin , given the current geographical ranges of what is now recognized as S. robustus and S. jallae it seems improbable that P. tanganyicae is either of these species. We thus consider it an error, and do not include this species in the synonymy, although further examination of this species is warranted.

Tsungwa is the common name in use in the local languages and by anglers.

Material examined. Holotype of S. robustus BMNH 1864.1.9.56

Other material: PSU 12920, 2 , 188.2 – 200.5 mm SL, Chembe Beach ; PSU 12921, 1, 178.7 mm SL, Nkhata Bay ; PSU 12922, 1 , 189.6 , Mwalamba Rocks , Chirombo Bay .

Diagnosis. The holotype is half of a skin (examined by JRS) collected from Lake Malaŵi by Kirk who accompanied Livingstone’s expedition ( Trewavas 1964). The presence of four or five scale rows between the posterior margin of the orbit and the ascending arm of the preoperculum, the presence of widely set unicuspid teeth on the jaws, widely separated gill rakers, and anal fins with egg ocelli places this species in Serranochromis . Breeding males of S. robustus possess ocelli that are restricted to the posterior 4–5 membranes of the anal fin, which delimits them from all other Serranochromis spp., which have ocelli throughout the anal fin in breeding males, with the exception of S. jallae . As stated above, S. robustus was shown to be delimited from all other species in the genus by several authors including Jackson (1961), Jubb (1961), and Trewavas (1964).

Serranochromis robustus generally has a longer lower jaw (50.7–59.6% HL) than S. jallae (49.2–52.7% HL); three specimens of S. jallae had a lower jaw length greater than 52% of the head length and two specimens of S. robustus possessed a lower jaw length of less than 52% of the head length. Serranochromis robustus is not as deepbodied as S. jallae as evidenced by the distance between the posterior insertion of the dorsal fin and the posterior insertion of the anal fin (13.4–15.1% SL in S. robustus vs. 14.9–18.4% SL in S. jallae ). Additionally, S. robustus has a narrower least caudal peduncle depth (10.9–12.8% SL) than S. jallae (11.3–14.2% SL); the least caudal peduncle depth of all S. robustus was less than 12.8% SL while, except for the smallest specimen of S. jallae (88.1 mm SL), the least caudal peduncle depth was greater than 13.2% SL. Serranochromis robustus has a smaller horizontal eye diameter (HED)(17.7–27.4% HL) than S. jallae (18.6–25.5% HL). Although the HED is subject to allometric growth, there is no overlap in the minimum polygons when HED is plotted against head length ( Fig. 1 ), and only the two smallest specimens of S. robustus have a HED greater than 19% HL. In general, S. robustus has more teeth in the outer row of the left lower jaw (14–23) than S. jallae (13–14); two specimens of S. robustus had 14 teeth with the remainder having 15 or more. Adults in breeding color of Serranochromis robustus ( Fig. 2 ) are blue/green laterally with a narrow yellow marginal band on the dorsal fin and usually a small yellowish tip to the upper caudal-fin lobe. Adults in breeding color of S. jallae are yellow/green laterally with a bright orange marginal band on the dorsal and caudal fins in fish from the Okavango River system, but creamy yellow bands in fish from the Upper Zambezi River system ( Fig. 3 ). The throat and belly of S. jallae becomes more intensely yellow-orange in breeding dress hence the local name ‘yellow-belly’. Rarely, specimens from the Okavango River in Namibia also have yellow rather than orange marginal bands (D. Tweddle, pers. comm.). Trewavas (1964) noted that breeding males of S. robustus robustus had no yellow on throat and belly while those of S. robustus jallae possessed yellow on throat and belly.

Description. Large robust Serranochromis with general body shape as in Fig. 2 . Principal morphometric and meristic data in Table 1 and documented above in diagnosis. Head elongate (36.2–38.0% SL). Cheek depth 26.1– 33.5% HL. Snout elongate (35.2–39.8% HL) and posterior end of lower jaw anterior to anterior margin of orbit. Two pored scales posterior to hypural plate, and 9–11 rows of scales on cheek. Outer arch of epibranchial with 4–5 gill rakers; outer arch of ceratobranchial with 10–12. Teeth in 2 series on upper and lower jaws. One or two scales between pectoral fin and posterior margin of opercle. Caudal fin emarginate and lacking marginal band in breeding adult males. Pectoral fin directly under origin of dorsal fin. Pelvic fin posterior to origin of dorsal fin.

Distribution and habitat. The native range of S. robustus is Lake Malaŵi and the outflowing Shire River and Lake Malombe — where it occupies mostly complex habitats in water shallower than 10 m. In southern Lake Malawi, S. robustus are generally associated with the rock/sand interface or, associated with submerged aquatic vegetation and among reed beds in shallow water and inlets. The Serranochromis species in the Luangwa River may be S. robustus based on photographs taken by anglers but specimens are needed to confirm this (Denis Tweddle, pers. comm.). Fish larger than 2 kg are rare. Serranochromis robustus was introduced from Lake Malawi into the Sand River Dam in Swaziland where it established and spread into the Komati River system in South Africa ( De Moor & Bruton 1988; Bills et al., 2004). Verbal reports (2019 pers. com., Erica Tovela, Maputo Museum) from Mozambique indicate the species has recently spread onto the Mozambique coastal plain.

Figures

FIGURE 1. Horizontal eye diameter as percent head length plotted against head length of Serranochromis robustus (+) and Serranochromis jallae (x).

FIGURE 2. Adult male of Serranochromis robustus. Photo by Denis Tweddle.

FIGURE 3. Adult males of Serranochromis jallae in breeding color (Okavango top; Upper Zambezi bottom). The anal fin in the top photo somewhat obscured by a shadow. Photos by Denis Tweddle.