Serranochromis jallae ( Boulenger 1896 )

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 : 130-132

Serranochromis jallae ( Boulenger 1896)

Hemichromis jallae Boulenger (1896)

Paratilapia zambesensis: Gilchrist &Thompson (1917)

Pelmatochromis ngamensis Gilchrist & Thompson (1917)

Serranochromis robustus: Jubb (1961) , Jackson (1961), Jubb (1967),

Serranochromis robustus jallae: Trewavas (1964)

Misidentified as Paratilapia thumbergi: Boulenger (1911)

The holotype is an 80.3 mm SL specimen collected from the upper Zambezi River ( Trewavas 1964) .

Nembwe is the widely used common name.

Material examined. Serranochromis jallae: SAIAB 72820, 6, 111.3– 144.4 mm SL, 16° 05’ 16” S, 23° 16’ 12” E, Zambia; SAIAB 71287 , 15° 34’ 1.9194” S; 23° 16’ 59.88” E, Kataba River , Kataba; SAIAB 7343 , 12° 14’ 34.998” S; 25° 34’ 26.0004” E, Mwombezhi River;

Diagnosis. 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. jallae 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. robustus . See above for the distinctions between S. jallae and S. robustus .

Description. Large robust Serranochromis with general body shape as in Fig. 3 . Principal morphometric and meristic data in Table 1 and documented above. Head elongate (35.8–39.7 % SL). Cheek depth 23.1–33.2 % HL. Snout elongate (33.9–38.6% HL) and posterior end of lower jaw anterior to anterior margin of orbit. Two to three pored scales posterior to hypural plate, and 7–9 rows of scales on cheek. Outer arch of epibranchial with 4 gill rakers; outer arch of ceratobranchial with 11–12. Teeth in 2 series on upper and lower jaws. Pectoral fin immediately posterior to posterior margin of opercle and directly under origin of dorsal fin. Pelvic fin posterior to origin of dorsal fin. Caudal fin rounded. Colour described above in diagnoses of S. robustus .

Distribution and habitat. Serranochromis jallae is native to the Okavango, upper Zambezi, Kafue, Kasai, and Zambian Congo systems; has been introduced to Lake Kariba, and elsewhere in Zimbabwe ( Poll 1967, Bell-Cross & Minshull 1988, Skelton 2001, Marshall 2011). Juveniles occur mostly on the floodplain and in lagoons, but larger adults appear to prefer mainstream habitats and are associated with in-stream structures such as woody debris, macrophyte beds, reeds, and eroded clay cliffs on outside bends of the rivers ( Winemiller 1991, Tweddle pers.com.). A movement study of 15 adult (32–49 cm TL) S. jallae on the upper Zambezi River demonstrated that the fish occupied relatively small home ranges, with individual fish utilizing a mean river stretch of 1330 m ( Thorstad et al., 2005). During low water levels, specimens of S. jallae were recorded in a variety of habitats in the mainstream of the river, but many moved onto adjacent temporary flooded areas during rising and high water; but did not undertake long-distance migrations onto the floodplains ( Thorstad et al. 2005).

Life history. Serranochromis jallae attains weights more than 4 kg (D. Tweddle, pers. comm.) but such large individuals are rare. Reproduction and diet of S. jallae in the upper Zambezi floodplain were described by Winemiller (1991). This mouthbrooder breeds in summer based on examination of gonads; S. jallae males attained sexual maturity at 275‐300 mm SL and females at 250–275 mm SL. Based on age estimates from scale annuli, maturity of S. jallae was at approximately 3 years in the Barotse floodplain and the average numbers of mature oocytes per female was 1165. Bowers are simple saucer-shaped depressions of ca. 30 cm diameter that are constructed on sandy substrates among vegetation ( van der Waal 1985). Analysis of stomach contents showed that interspecific diet overlap with other serranochromines was low among both immature and mature size classes of Serranochromis . Adult size classes of S. jallae are primarily piscivorous with small catfishes (e.g., Synodontis spp.) dominating the diet on the Barotse floodplain ( Winemiller 1991).

Further notes on distinction between S. robustus and S. jallae . When overall shape differences in the two species were quantified, there was no overlap in the minimum polygon clusters, when the SPC2 (morphometric data) were plotted against the PC1 of the meristic data ( Fig. 4 ). Size accounted for 96% of the observed variance with second principal component 2.4%. Variables with the highest loadings on the SPC2 were caudal peduncle length (0.59), vertical eye diameter (0.37) and least caudal peduncle length (-0.38). The first principal component of the meristic data accounted for 43.7% of the total variance. Variables with the highest loadings on the first principal components were number of gill-rakers on the ceratobranchial (0.51), dorsal-fin rays (0.52), and lateral-line scales (0.45). Thus, morphological, color, and shape characteristics all support the recognition of two distinct species.

Figures

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.

FIGURE 4. Sheared second principal components (morphometric data) plotted against the first principal components of the meristic data for Serranochromis robustus (+) and Serranochromis jallae (x). The minimum polygon clusters are bounded by 95% confidence levels.