Haplochromis mentatus Regan, 1925

Vranken, Nathan, Steenberge, Maarten Van, Heylen, Annelies, Decru, Eva & Snoeks, Jos, 2022, From a pair to a dozen: the piscivorous species of Haplochromis (Cichlidae) from the Lake Edward system, European Journal of Taxonomy 815, pp. 1-94 : 18-24

Haplochromis mentatus Regan, 1925

Figs 1–2 , 8–10 ; Table 1

Haplochromis mentatus Regan, 1925: 188 , pl. 10.

Haplochromis mentatus – Greenwood 1973: 204.

Harpagochromis mentatus – Greenwood 1980: index.

Differential diagnosis

Species with a piscivorous morphology; body shallow [BD 29.0–32.3 (mean 31.2) % SL]; snout very acute in dorsal and lateral views; outer oral teeth few and large [UOT 28–46 (median 36)]; vertebrae many (Va+Vc 30–32); dominant males yellow-green with a red anterior part of flank.

Amongst piscivorous species from the Lake Edward system, H. mentatus differs from H. latifrons sp. nov. by the combination of a longer dorsal fin base [DFB 50.3–54.2 (52.3) vs 47.2–50.1 (49.0) % SL], a weakly vs strongly prominent premaxillary pedicel, a steeper sloping lower jaw side (30–45° vs 25– 30°), and absence vs presence of a well-defined mid-lateral band.

It differs from H. rex sp. nov. and H. aquila sp. nov. by the combination of a longer caudal peduncle [CPL 15.7–17.5 (16.6) vs 13.5–16.2 (14.8–15.0) % SL], a gentler sloping snout (30–35° vs 35–50°), and dominant males yellow-green with a red anterior part of flank vs cream-coloured with an orange operculum, or light grey with a black head, respectively; further from H. rex sp. nov. by a larger number of infraorbital cheek scales [ChSi 3–4 vs 5–6 (rarely 4 or 7)]; further from H. aquila sp. nov. by smaller eyes [ED 25.4–29.9 (27.2) vs 30.0–31.5 (30.6) % HL].

It differs from H. simba sp. nov. by the combination of a broader interorbital area [IOW 51.3–61.0 (55.5) vs 45.5–50.4 (48.1) % HW], a larger number of outer upper jaw teeth [UOT 28–46 (36) vs 22–31 (27)], absent to weakly prominent vs strongly prominent premaxillary pedicel and mentum, and dominant males yellow-green with a red anterior part of flank vs yellow with an orange anterior part of flank.

It differs from H. glaucus sp. nov. by the combination of a longer caudal peduncle [CPL 15.7–17.5 (16.6) vs 13.4–16.1 (14.8) % SL], a narrower lower pharyngeal bone [LPW 83.6–85.7 vs 93.3–95.1% LPL], a slightly shorter pre-pectoral distance [PrP 33.1–38.2 (36.0) vs 36.4–39.4 (38.1) % SL], and dominant males yellow-green with a red anterior part of flank vs uniformly blue.

It differs from H. kimondo sp. nov. and H. quasimodo sp. nov. by the combination of a narrower head [HW 39.4–42.3 (40.8) vs 42.0–48.1 (45.1–45.3) % HL] and dominant males yellow-green with a red anterior part of flank vs grey dorsally and yellow or blue-black ventrally; further from H. kimondo sp. nov. by a very acute vs blunt snout, and a gentler sloping snout (30–35° vs 40–50°); further from H. quasimodo sp. nov. by a shallower body [BD 27.2–30.1 (28.6) vs 33.5–41.7 (37.4) % SL].

It differs from H. falcatus sp. nov. by the combination of a shorter predorsal distance [PrD 33.3–36.4 (35.3) vs 36.9–41.1 (39.5) % SL], a shorter head [HL 33.4–37.0 (35.1) vs 36.6–39.6 (38.2) % SL], straight to weakly recurved vs strongly recurved outer oral teeth, a steeper lower jaw side (30–45° vs 15–25°), absence vs presence of well-defined mid-lateral and dorsal-lateral bands.

It differs from H. curvidens sp. nov. and H. pardus sp. nov. by the combination of a deeper lacrimal [LaD 18.1–20.9 (19.7) vs 16.0–18.3 (16.7–17.3) % HL] and smaller eyes [ED 25.4–29.9 (27.2) vs 29.4–34.1 (30.4–31.9) % HL]; further from H. pardus sp. nov. by dominant males yellow-green with a red anterior part of flank vs speckled to uniformly black.

It differs from H. squamipinnis by the combination of large vs small outer oral teeth and a smaller number of outer upper jaw teeth [UOT 28–46 (36) vs 46–71 (58)], a shallower body [BD 29.0–32.3 (31.2) vs 32.4–39.3 (35.7) % SL], absence vs presence of minute scales on proximal part of dorsal fin, and dominant males yellow-green with a red anterior part of flank vs uniformly slate blue.

Etymology

Specific name not explained in original description, probably derived from the Latin ‘ mentum ’for ‘chin’; probably referring to the protruding lower jaw (i.e., projecting lower jaw sensu Regan 1925).

Material examined

Holotype UGANDA • ♀, 93.1 mm SL; Lake Edward ; 1924; J.C. Phillips leg.; MCZ 31523 .

Other material UGANDA – Lake Edward • 1 ♂, 94.4 mm SL; ‘Coral Reef’, hard substrate at mouth of Nyamugasani River ; 0°10′08.4″ S, 29°49′37.2″ E; 21 Oct. 2016; HIPE1 exped. leg.; RMCA 2016.035.P.0255 • 1 ♂, 2 ♀♀, 111.3–128.1 mm SL; Rwenshama , rocky shore; 0°24′05.7″ S, 29°46′35.1″ E; 25 Mar. 2017; HIPE2 exped. leg.; RMCA 2017.006.P.0408 to 0410 • 3 ♂♂, 111.5–118.5 mm SL; Kayanja offshore; 0°05′34.8″ S, 29°45′28.8″ E; 30 Mar. 2017; HIPE2 exped. leg.; RMCA 2017.006.P.0411 to 0413 • 1 ♂, 117.7 mm SL; same collection data as for preceding; RMCA 2017.006.P.0414 • 1 ♀, 1 ♂, 87.2–133.2 mm SL; islands near Katwe ; 0°10′04.9″ S, 29°52′27.4″ E; 18 Jan. 2018; HIPE3 exped. leg.; RMCA 2018.008.P.0380 to 0381 • 1 ♀, 1 ♂, 87.8–95.5 mm SL; same collection data as for preceding; RMCA 2018.008.P.0383 to 0384 • 2 ♀♀, 108.3–137.2 mm SL; 0°24′16.0″ S, 29°46′24.8″ E; 24 Jan. 2018; HIPE3 exped. leg.; bought at Rwenshama landing site; RMCA 2018.008.P.0387 to 0388 • 1 ♂, 137.1 mm SL; 0°24′16.0″ S, 29°46′24.8″ E; 1 Feb. 2018; HIPE3 exped. leg.; bought at Rwenshama landing site; RMCA 2018.008.P.0389 . – Lake George • 1 ♂, 107.9 mm SL; ‘Bivalve Site’, north of Kankurunga Island ; 0°00′39.6″ N, 30°08′13.2″ E; 29 Mar. 2017; HIPE2 exped. leg.; RMCA 2017.006.P.0424 • 1 ♀, 92.1 mm SL; Kashaka bay , north of inlet; 0°04′52.2″ S, 30°10′47.3″ E; 2 Feb. 2018; HIPE3 exped. leg.; RMCA 2018.008.P.0394 • 2 ♀♀, 94.0, 120.0 mm SL; same collection data as for preceding; RMCA 2018.008.P.0395 to 0396 .

Description

Based on 20 specimens (87.2–137.2 mm SL); body shallow ( Table 1 ) and oval; caudal peduncle long ( Fig. 8 ). Head very narrow and with a straight dorsal outline and a slightly convex nape; cheek average in depth; lacrimal deep; eye small; interorbital area narrow in comparison to generalised H. elegans (but relatively broad for a piscivorous species). Snout long, very acute in dorsal and lateral views, and slopes very gently at 30–35°; premaxillary pedicel long and weakly prominent. Jaws long, very narrow, acute in dorsal view, relatively slim, and isognathous; gape large and slopes gently at 20–30°; posterior tip of maxilla reaches a vertical just past anterior margin of orbit. Lower jaw slim and with a straight to weakly concave ventral outline in lateral view, mental prominence absent or weakly developed, and lower jaw side steep with an inclination of 30–45° to horizontal in anterior view. Upper jaw expanded anteriorly and weakly ventrally. Lips and oral mucosa large. Neurocranium shallow, ethmo-vomerine block decurved, preorbital region very shallow (18–22% NL), orbital region shallow (28–31% NL), and supraoccipital crest shallow and wedge-shaped ( Fig. 9b ).

Outer oral teeth few, unicuspid, and large. Necks stout, conical, and straight; crowns slightly recurved and acutely pointed. Dental arcades acute. Outer teeth widely and irregularly set with neck-distances of ½–2 neck-widths. In upper jaw, 1–3 posteriormost teeth slightly enlarged. Inner teeth small, strongly recurved, unicuspid, and acutely pointed. Tooth bands very slender crescent-shaped with 1–2 rows of inner teeth, and narrow posteriorly until only outer row remains past ⅔ length of tooth band in upper jaw, past ½ length of tooth band in lower jaw. Inner teeth closely and regularly set on 1–2 outer neck-widths from outer row; implantation recumbent; size uniform.

Lower pharyngeal bone long, narrow, slim, and shallow over whole length ( Fig. 10 ). Pharyngeal teeth relatively large and slender; major cusps acutely pointed; cusp gaps concave; minor cusps and cusp protuberances mostly absent. Teeth in two median longitudinal rows equal in size and form to lateral teeth, 11 in each row. Posterior transverse row with 14–21 teeth, implanted recumbently with a lateral inclination; major cusps nearly straight, bluntly pointed, and laterally compressed; minor cusps mostly absent.

Chest scales small; transition to larger flank scales gradual. In some specimens, basal parts of membranes between anal-fin spines covered by few (1–3) minute, ellipsoid scales (nearly invisible to naked eye); remaining part of anal and dorsal fins scale-less. Minute scales on proximal half of caudal fin.

Caudal fin emarginate; dorsal and anal fins reach to between vertical through caudal-fin base and two scales anterior to this vertical. Pectoral and pelvic fins reach to between genital opening and first anal-fin spine; pelvic fin reaches to third anal-fin spine in males; first branched pelvic-fin ray slightly elongated in all specimens.

Ceratobranchial gill rakers in outer row of first gill arch short, stout, and simple; posteriormost rakers mostly anvil-shaped or weakly bifid. Epibranchial rakers slender and simple.

Colouration in life

Dominant males: body, cheek, and lower jaw yellow-green with blue sheen; flank, dorsal part of head, and operculum bright red; belly and chest speckled black ( Fig. 9c ). Snout and lips dusky; branchiostegal membrane black; eye with (dark) grey outer ring and yellow inner ring. Flank with very faint midlateral, dorsal-lateral, and 5–7 vertical stripes; nostril stripe faint. Dorsal and anal fins dusky and with black lappets; anal fin with a crimson distal part and 2 small orange egg spots with dusky rings. Caudal fin dusky with a crimson distal part. Pectoral fin dusky yellow and pelvic fin black.

Females and juveniles: dorsal parts of body and operculum green-yellow; gradual transition to white ventral parts of body and operculum, cheek, and lower jaw; flank with a blue sheen ( Fig. 9d ). Lacrimals, snout, and lips dusky green; lacrimals with a blue sheen; eye with (dark) grey outer ring and yellow inner ring. Nostril stripe faint. Dorsal fin dusky and with black lappets; anal fin white-yellow and with 1–2 small spots resembling egg-spots; caudal fin dusky. Pectoral fin yellowish; pelvic fin white-yellow.

Preserved colouration

In dominant males, body uniformly brown, pectoral fin dusky, pelvic fin black, and anal fin dusky and with 1–2 small egg-spots ( Fig. 9a ). In females, dorsal part of body yellowish, gradual transition to white ventral part of body, cheek light yellow, pectoral fin hyaline, pelvic fin yellowish, and anal fin with a white base and a dusky distal part. In all specimens, snout dusky and nostril, interorbital, and lacrimal stripes faint. Dorsal fin dusky and with black lappets; caudal fin dusky.

Distribution and ecology

Endemic to Lake Edward system, found in offshore areas, mostly in shallow waters. Based on its morphology, most probably a piscivorous species.

Systematic comment

Both Trewavas (1933) and Greenwood (1973) noted that the holotype of H. mentatus strongly resembled H. squamipinnis . Greenwood recognised that this specimen deviated from H. squamipinnis in that it lacked minute scales on the basal parts of the dorsal- and anal-fin membranes, but he was uncertain about the relevance of this difference. We found this trait to be present in all H. squamipinnis specimens. We discovered that abdominal vertebrae 6–9 of the holotype of H. mentatus are broken and the vertebral column kinked ( Fig. 9b ). This resulted in the holotype of H. mentatus having an aberrant rhomboidshaped instead of an oval body as in other specimens of its species. Because of this deformation, the specimen indeed resembles H. squamipinnis in overall habitus.

Figures

Fig. 1. The Lake Edward system, consisting of Lakes Edward and George that are connected through the Kazinga Channel. The catch localities of all examined specimens are indicated: Haplochromis sp. ‘latifrons’ (), H. mentatus Regan, 1925 (), H. sp. ‘rex’ (), H. sp. ‘simba’ (▼), H. sp. ‘glaucus’ (), H. sp. ‘aquila’ (), H. sp. ‘kimondo’ (●), H. sp. ‘falcatus’ (), H. sp. ‘curvidens’ (), H. sp. ‘pardus’ (), H. sp. ‘quasimodo’ (▲), and H. squamipinnis Regan, 1921 (█). The type localities of H. mentatus and H. squamipinnis are not shown as the exact locations are unknown.

Fig. 2. a. Differences in total number of outer teeth and premaxillary dentition between the macro- and microdontic groups of piscivores from the Lake Edward system.b. Schematic presentation of the dominant male colour patterns in life, in the various groups studied. For H. sp. ‘latifrons’ the female and for H. sp. ‘curvidens’ the non-dominant colour patterns are shown, as those of dominant males are unknown.

Fig. 8. Haplochromis mentatus Regan, 1925, holotype, ♀, 93.1 mm SL (MCZ 31523) reconstructed with a straightened vertebral column. Drawn by N. Vranken.

Fig. 9. Haplochromis mentatus Regan, 1925. a. Photograph of preserved holotype (MCZ 31523; 93.1 mm SL). b. X-ray image of holotype. c–d. Photographs of freshly caught specimens. c. Dominant male (RMCA 2017.006.P.0424; 107.9 mm SL). d. Female (RMCA 2018.008.P(HP2453); 116.2 mm SL) to illustrate the live colour patterns. The contrast was slightly enhanced.

Fig. 10. Haplochromis mentatus Regan, 1925 (RMCA 2018.008.P.0389; 137.1 mm SL). a. Dorsal view of the lower pharyngeal jaw. b. Lateral view of the lower pharyngeal jaw.