Lacustricola johnstoni ( Guenther , 1894)

Braganca, Pedro H. N., Zeeventer, Ryan M. van, Bills, Roger, Tweddle, Denis & Chakona, Albert, 2020, Diversity of the southern Africa Lacustricola Myers, 1924 and redescription of Lacustricola johnstoni (Guenther, 1894) and Lacustricola myaposae (Boulenger, 1908) (Cyprinodontiformes, Procatopodidae), ZooKeys 923, pp. 91-113 : 91

Lacustricola johnstoni ( Guenther, 1894) Figures 3 , 4

Haplochilus johnstoni Günther, 1894: 627 [original description: Mangochi (former Fort Johnston), Malawi].

Material examined.

BMNH 1893.11.15.95, Lectotype; BMNH 1893.11.15.92-94,96-99, 7 Paralectotypes; Mangochi (former Fort Johnston), Malawi. Examined by photographs and x-rays - SAIAB 35820, 18 (5 C&S), 24.7-35.4 mm SL; Upper Shire River, Mangochi, Malawi, 14°26'60"S, 35°15'60"E; col: D. Tweddle & N. G. Willoughby; 19 Sep. 1971. - SAIAB 8311, 3, 31.3-32.5 mm SL; Shire River, Liwonde, Malawi; col: D. Tweddle & N. G. Willoughby; 20 Oct. 1975. - SAIAB 34384, 1, 29.1 mm SL; Shire River, Liwonde Barrage, Malawi, 15°04'S, 35°13'E; col: D. Tweddle & P. Skelton; 26 Oct. 1989. - SAIAB 34388, 1, 35.7 mm SL; Monkey Bay, Lake Malawi, Malawi, 14°04'S, 34°55'E; 17 Oct. 1989. - SAIAB 40800, 15 (4 C&S), 30.1-33.2 mm SL; Bridge over Dwambadzi River, Malawi, 12°14'S, 33°59'E; col: D. Tweddle & P. Skelton; 06 Sep. 1992. - SAIAB 11237, 7, 26.2-36.2 mm SL; Monkey Bay, Lake Malawi, Malawi, 14°3'00"S, 34°55'00"E; col: D.H. Eccles; 31 Oct. 1974. - SAIAB 11876, 8, 27.2-34.7 mm SL; Shire River, Liwonde Barrage, Malawi, 15°3'37"S, 35°13'7"E; col: D. Tweddle & T. Makinen; 27 May. 2011.

Diagnosis.

" Lacustricola " johnstoni is distinguished from all congeners from the " L. " katangae clade by the absence of a zigzag black mark along the flank (vs. presence); and from congeners belonging to the " L. " hutereaui clade by the absence of a barred dorsal, anal and caudal-fins and also by the absence of a conspicuous reticulate pattern on scale margins. It is further distinguished from all congeners except " L. " myaposae and " L. " moeruensis by the presence of orange dorsal, anal and caudal-fins in females (vs. hyaline); it is distinguished from " L. " myaposae by the presence of a bluish colouration in the posterior region of flank (vs. light purple colouration); a slender body profile, male body depth 20.6-24.4% of SL (vs. 26.0-30.9% of SL), female body depth 19.7-22.5% of SL (vs. 22.8-25.1% of SL); a shorter dorsal-fin base length in males 8.7-11.6% of SL (vs. 11.9-13.1% of SL) and in females 7.3-10.1% of SL (vs. 10.8-11.6% SL); a less deep head in males 61.9-67.0% of HL (vs. 70.7-79.8% of HL) and in females 59.4-63.5% of HL (vs. 66.6-69.6% of HL); and a hyaline pectoral-fin in males (vs. orange). Other morphometric characters presenting a slight overlap but useful in distinguishing " L. " johnstoni from " L. " myaposae are: a comparatively narrow caudal peduncle, depth of 12.6-14.5% of SL in males and 11.2-12.7% of SL in females (vs. 14.0-17.1% of SL in males and 12.9-13.7% of SL in females); a comparatively elongated caudal-fin, 30.1-33.8% of SL in males and 28.9-31.2% of SL in females (vs. 27.5-30.2% of SL in males and 25.3-28.5% of SL in females); and a comparatively deep, laterally compressed head, 57.1-63.2% of HL in males and 59.0-64.7% of HL in females (vs. 63.1-67.9% of HL in males and 65.3-68.1% of HL in females). " Lacustricola " johnstoni is distinguished from " L. " moeruensis by a comparatively slender body and a more backward positioned dorsal-fin, first proximal radial of dorsal-fin between neural spine of vertebrae 16 and 17 (vs. 13 and 14).

Description.

Morphometric data are presented in Table 1 . Maximum recorded adult size 35.6 mm SL. Dorsal profile of body approximately straight to slightly convex from snout tip to dorsal-fin origin; convex along dorsal-fin base. Ventral profile convex from lower jaw to beginning of anal-fin base; slightly convex along the anal-fin base and nearly straight on caudal peduncle. Anterior portion of body laterally compressed, becoming more compressed behind anal-fin origin.

There is clear sexual dimorphism in fin shape and size (Figs 3 , 4 ). In males, dorsal-fin is rounded and elongated, almost reaching the caudal-fin base; its origin in vertical between 7th and 9th anal-fin rays; anal-fin rounded and elongated, reaching middle of the caudal peduncle. Pelvic-fin length variable, reaching between urogenital papillae aperture and the base of third anal-fin ray. In females, dorsal and anal-fins are not elongated and do not extend posteriorly to caudal-fin base. Caudal-fin slender in both sexes. Pectoral-fin elliptical, in both males and females, its posterior margin reaching vertical just behind pelvic-fin base. In females, pelvic-fin shorter than in males, tip reaching region just before urogenital opening. In both males and females, dorsal-fin rays 7(17), 8(13) and 9(2); anal-fin rays 12(4), 13(12), 14(14) and 15(2); caudal-fin rays 19(2), 20(10), 21(17), 22(2) and 23(1); pectoral-fin rays 12(13), 13(18) and 14(1); pelvic-fin rays 6.

Frontal squamation G-patterned (Fig. 5 ). Head neuromasts placed in shallow grooves. Cephalic lateral line system: anterior portion of supraorbital sensory canal open, with three neuromasts, anteriormost one anteriorly displaced from the other two; posterior portion open, with three exposed neuromasts; anterior infra-orbital canal partially closed, with two pores and one free neuromast, but in juveniles and subadults all anterior infraorbital canal can be open; median portion of infra-orbital region with series of nine to eleven minute neuromasts; posterior infra-orbital canal closed, with two pores; preopercular canal closed in both dorsal and ventral portions with seven or eight pores; mandibular canal represented by two neuromasts, one in vertical through corner of mouth and the other anteriorly positioned in the lower jaw ventral portion. Longitudinal series of scales 27(3), 28(18), 29(9); transverse series of scales 7; circumpeduncular scales 10; predorsal scales 17(1), 18(18), 19(11).

Osteology.

Osteological structures are presented in Fig. 6 . Mesethmoid and vomer absent. Frontals, anterior margin, extending anteriorly between nasals. Parasphenoid medial process short, not contacting pterophenoid; anterior margin rounded. Lateral ethmoid overlapping with anterior portion of parasphenoid. Posterior process of supraoccipital long, reaching first vertebra. Lachrymal rectangular. Premaxillary and dentary teeth well developed. Retroarticular triangular or subtriangular. Dentary deep. Dorsal process of maxilla broad overlapping the ascending process of premaxilla; ventral process greatly reduced, consisting of a rounded ventromedial bulge. Ventral arm of maxilla broad, laterally expanded. Medial surface of premaxilla ascending process with a straight or slightly concave profile. Entopterygoid posterior portion and sympletic bone keel deep. Opercle triangular, anterodorsal process present. Anterior process of anterior ceratohyal does not extend ventrally to ventral hypohyal. Urohyal ventral margin concave. First and second basibranchials with expanded lateral bone flanges. Cartilaginous portion of basihyal shorter than osseous portion. Fourth ceratobranchial anterior third with teeth. Second pharyngobranchial plate with teeth. First epibranchial base, broad, more than three times anterior portion width. Supracleithrum rounded. Posttemporal rod-like, ventral arm absent. Cleithrum bony flange not covering scapula foramen. Ventral postcleithrum, slender, similar in width to adjacent first pelural rib. Basipterygium, posterior process, shorter or about the same size of medial process. Anal-fin proximal radials about the same length and parallel to each other. Hypurals completely fused. Parahypural proximal end overlapping the preural centrum. Total vertebrae 30(4) and 31(5), precaudal 13(2) and 14(7) and caudal 16(1), 17(4) and 18(4). First proximal radial of dorsal-fin between neural spine of vertebrae 16 and 17. First proximal radial of anal-fin between pleural rib of vertebrae 11 and 13. Gill rakers on first branchial arch 10(1) and 11(3). Branchiostegal rays 5.

Colouration in alcohol.

Overall colouration of body pale brown yellow with minute chromatophores sparsely distributed, and some organised chromatophores forming an inconspicuous reticulate pattern along flank scales margin (Fig. 3 ). Ventral surface scarcely pigmented. Pale brown chromatophores along whole mid-body line of flank. Head overall colouration yellowish brown. Brown chromatophores on dorsum of head. Minute chromatophores concentrated in the lower jaw and pre-orbital region, forming a distinct darker region. Iris silver, darker close to pupil; dark pigment concentrated on dorsal margin of eye. All fins hyaline in females, with melanophores sparsely concentrated only on fins membranes and along fin rays; melanophores forming small inconspicuous spots on male dorsal-fins, rarely forming two distinct bands; melanophores forming two distinct parallel dark bands in the anal-fin medial portion; region close to anal-fin rays insertion hyaline; caudal-fin with conspicuous dark blotches in the middle rays that could be organised in distinct bands or not; pectoral and pelvic-fin with melanophores sparsely concentrated on fins membranes and along fin rays. Female urogenital opening pocket scales with dark brown chromatophores.

Colouration in life.

Males (Fig. 4A ). Flanks bright blue, with small scattered bright green dots. Cupric iridescent blotch on region just posterior to pectoral-fin. Dorsum yellow-brown. Ventral surface white between head and region anterior to pelvic-fin origin; bright blue between pelvic-fin and the end of the anal-fin insertion; ventral region of caudal peduncle whitish yellow. Side of head predominantly bluish silver, dorsal portion yellow-brown, post-orbital region with a distinct green bright blotch. Iris dark grey, light yellow close to pupil. Eye bright silver on dorsal portion. Lower jaw and pre-orbital region dark brown-grey, forming a distinct horizontal band. Pectoral-fin hyaline; all other fins yellowish brown with brown dots on fins arranged in distinct rows. Dorsal-fin with two to four rows; anal-fin with two to three rows; and caudal-fin with four to five rows, but in some specimens the brown dots are scattered over the fin and not arranged in distinct rows. Some males may present a distinct black distal margin on anal, dorsal and caudal-fins.

Females (Fig. 4B ). Flanks bright blue. Cupric iridescent blotch on region just posterior to pectoral-fin. Dorsum yellow-brown. Venter white between head and region just anterior to urogenital opening; bright blue between region just anterior to urogenital opening and anal-fin insertion; whitish yellow along the anal-fin insertion to caudal peduncle. Scales around urogenital opening covered with dark chromatophores. Side of head predominantly bluish silver, ventral portion white, dorsal portion yellow-brown, post-orbital region with a distinct green bright blotch. Iris dark grey, light yellow close to pupil. Eye bright silver on dorsal portion. Lower jaw and pre-orbital region dark brown-grey, forming a distinct horizontal band. Pectoral and pelvic-fins hyaline; dorsal-fin orange, distal margin hyaline; anal-fin base hyaline, distal portion orange; caudal-fin orange, distal region hyaline.

Distribution and habitat.

" Lacustricola " johnstoni is a widespread species occurring in the Lower, Middle and Upper Zambezi River, including the Shire River and Lake Malawi, the Limpopo River, and is also present in the Okavango system (Fig. 2 ). The species is usually found associated with marginal vegetation along the banks of small and large rivers, or in swampy areas, as well as along the shores of Lake Malawi and Lake Kariba.

Figures

Figure 2. Southern Africa " Lacustricola " distribution maps. Spots correspond to the exact localities for the haplotypes included in this study, and the shaded area refers to the inferred distribution for each species. Map A yellow - " Lacustricola " hutereaui; grey - " L. " johnstoni; brown - " L. " myaposae; and purple - " L. " jubbi. Map B dark green - " L. " macrurus; orange - " L. " mediolateralis; red - " L. " katangae; light blue - " L. " centralis; blue - " L. " aff. johnstoni ' Okavango'; light green - " L. " aff. johnstoni ' Congo'.

Figure 3. " Lacustricola " johnstoni preserved colouration: A male SAIAB 118776, 34.7 mm SL B female SAIAB 118776, 32.0 mm SL; from Shire River at Liwonde Barrage, Malawi.

Figure 4. " Lacustricola " johnstoni colouration in life: A male SAIAB 118776, 31.0 mm SL B female SAIAB 118776, 26 mm SL; from Shire River at Liwonde Barrage, Malawi.

Figure 5. Cephalic pores and head squamation pattern: A, B head dorsal and lateral view of " L. " johnstoni C head lateral view of " L. " myaposae.

Figure 6. Osteological plate of " L. " johnstoni (SAIAB 35820) from the Upper Shire River, Mangochi, Malawi. A Lachrymal B neurocranium, ventral view C neurocranium dorsal view D ventral post-cleithrum and first pleural rib, lateral view E anal-fin radials and proximal radials, left lateral view F caudal-fin skeleton, left lateral view G dorsal-fin radials and proximal radials, left lateral view H left branchial arches ventral portion, ventral view I right dorsal portion of branchial arches, ventral view J urohyal, left lateral view K left basipterygium, dorsal view L left shoulder girdle, lateral view M right hyoid bar, lateral view N left jaws, jaws suspensorium and opercular apparatus, lateral view. Scale bars: 1 mm.