Lacustricola margaritatus, Nagy & Watters, 2022

Nagy, Béla & Watters, Brian R., 2022, Lacustricola margaritatus, a new species of lampeye from the Lake Victoria and Lake Kyoga basins in eastern Africa (Cyprinodontiformes: Procatopodidae), Zootaxa 5128 (1), pp. 44-60 : 50-55

Lacustricola margaritatus , new species

http://zoobank.org/ urn:lsid:zoobank.org:act:6901C1A0-3646-4B4C-9D39-D1B21695335E

( Figs. 3–6 )

Aplocheilichthys centralis ‘Kasama TZ 91/135’, non Seegers, 1996: Seegers, 1997: 26.

Aplocheilichthys centralis ‘U 88/5’, non Seegers, 1996: Seegers, 1997: 26.

Aplocheilichthys centralis , non Seegers, 1996: Langton, 2004: 89–90; Sayer et al. 2018: 210.

Aplocheilichthys cf. centralis ‘U 88/17’: Seegers, 1997: 26; Langton, 2004: 88.

Aplocheilichthys pumilis , (sic!) non ( Boulenger, 1906): Lampke, 1975: 97.

Aplocheilichthys pumilus , non ( Boulenger, 1906): Copley, 1958: 113 (in part); Greenwood, 1958: 95 (in part); Meinken, 1971: 433; Wildekamp, 1979: 87; Wildekamp et al. 1986: 182 (in part); Seegers et al. 2003: 40 (in part).

Aplocheilichthys sp. aff. centralis , ‘Masindi’: Seegers, 1996: 261.

Aplocheilichthys sp. : Seegers, 1989: 6; Langton, 2004: 39.

Aplocheilichthys sp. UG 90-12: Langton, 2004: 47.

Lacustricola centralis (non Seegers, 1996): Nagy, 2020a: 46; Nagy, 2020b: 71.

Holotype. RMCA 2021.011 .P.0001, male, 26.5 mm SL; Tanzania: Lake Victoria basin : ephemeral swamp about 3.5 km west of Kiziramiaga township, 2.155611 S, 31.632500 E; B. Nagy, K. Østergaard & G. Petneházy, 31 May 2019 [field code: TZN 19-4 ].

Paratypes. RMCA 2021.011 .P.0002, male, 26.4 mm SL; RMCA 2021.011 .P.0003–4, 2 females, 25.2–25.3 mm SL; collected with the holotype.— RMCA 2021.011 . P.0005, male, 28.0 mm SL; Tanzania: Lake Victoria basin : extensive ephemeral swamp 11 km south of Sanje, 2 km south of Kakuto , 0.877883 S, 31.463367 E; B. Watters , R. Wildekamp & B. Cooper, 16 June 1999 [field code: UG 99-37 ] .— RMCA 2021.011 . P.0006–7, 2 males, 22.1–26.1 mm SL; Uganda: Lake Victoria basin : Lutembe Bay, just east of Namulanda , 0.159806 N, 32.561111 E; B. Nagy & K. Østergaard, 12 June 2021 [field code: UGN 21-1 ] .— RMCA 2021.011 . P.0008, male, 26.4 mm SL; Uganda: Lake Kyoga basin: 83 km NW Mbale, just NW of Kapiri, 1.661400 N, 33.768700 E; B. Watters , R. Wildekamp & B. Cooper, 5 June 1999 [field code: UG 99-12 ] .— RMCA 2021.011 . P.0009, male, 23.0 mm SL; Uganda: Lake Kyoga basin: ephemeral pool about 41 km north of Soroti, just north of Kuju , 2.045767 N, 33.603817 E; B. Watters , R. Wildekamp & B. Cooper, 7 June 1999 [field code: UG 99-18 ] .

Diagnosis. Lacustricola margaritatus belongs to the genus Lacustricola sensu stricto that includes small to medium sized species with moderately deep body, presenting moderate dimorphism and pronounced dichromatism: male with iridescent light blue scales and deeply coloured unpaired fins; female dark grey scale margins and dark grey patches on scales along mid-longitudinal series creating a narrow dark grey stripe. Lacustricola margaritatus is distinguished from all other species of the genus by the following unique combination of characters: male live body colour pattern with vertically elongated iridescent light blue patches at scale centres (vs. rounded), forming a striped appearance of dotted lines on the flank, particularly evident in two or three series below midlongitudinal line (vs. absent or irregular stripes); male having deeply coloured unpaired fins with orange-brown in proximal and median parts (vs. blue or green or dark grey to black) and black narrow distal band (vs. absent); male with yellow colouration on pectoral fin base (vs. silver); both sexes showing inconspicuous postopercular blotch (vs. absent); and in both sexes the cephalic sensory system entirely situated in open grooves at all levels (vs. partially closed tubular in L. pumilus ).

Description. General body features illustrated in Figures 3–6 . Morphometric and meristic characters of holotype and paratypes are summarised in Table 1 . Distinct sexual dimorphism is shown in certain body features, as well as size and shape of fins.

Males: small species, maximum observed size 28.0 mm SL. General body shape laterally compressed and moderately deep. Greatest vertical body depth in front of pelvic-fin origin (25.7–28.7 % SL) and shallowest at midportion of caudal peduncle (14.9–16.6 % SL). Greatest body width at pectoral-fin base with body progressively narrowing towards caudal-fin base. Dorsal profile straight from snout to nape and slightly convex from nape to origin of dorsal-fin ray, slightly convex along dorsal-fin base, and straight from base of dorsal fin to caudal fin. Ventral profile straight to slightly convex from lower jaw to operculum, convex from operculum to origin of pelvic fin, slightly convex from base of pelvic fin to last anal-fin ray, straight to slightly concave on ventral midline of caudal peduncle. Caudal peduncle relatively deep, length 139–147 as % of its depth. Anus directly anterior to anal-fin origin.

Head short, laterally compressed, slightly deeper than wide (head width 81–90 as % of its depth). Snout slightly rounded, significantly smaller than eye diameter (snout length 15–21 % HL). Mouth superior, oblique in profile. Jaws not equal, lower jaw longer than upper, posterior end of corner of mouth at same level as centre of eye. Premaxilla and dentary with many irregularly distributed conical teeth. Orbit moderately large (33–40 % HL).

Dorsal-fin set posteriorly, origin posterior to anal-fin origin, both fins originating posterior to mid-length of body. Dorsal and anal fins rounded trapezoidal shape, posterior rays longer than anterior rays. Dorsal fin rays 9–11; anal fin rays 13–16. Pectoral fin subtriangular, with 12 rays, insertion relatively high and posterior to margin of opercular opening; base oblique, upper fin rays placed anteriorly to lower fin rays. Pelvic fin rounded rhomboid, sub-abdominal, origin slightly anterior to mid-length between insertions of pectoral and anal fins, with 6 rays, reaching urogenital papilla aperture. Caudal fin large and rounded, with 13–14 branched rays, plus four or five dorsal and ventral procurrent rays.

Scales cycloid, body and head entirely scaled, except for ventral portion of head. Scales in mid-longitudinal series, 25–27, plus two to four transverse rows of scales on caudal-fin base, extending into medial portion of caudal. Transverse rows of scales in front of dorsal-fin origin, 7–8; scale rows around caudal peduncle, 10.

Three frontal neuromasts, typically in shallow grooves. Cephalic sensory system at preorbital level open in shallow grooves with two neuromasts; infraorbital series with 10 to 15 minute neuromasts; postorbital system open in shallow groove with two neuromasts; preopercular sensory systems open in shallow groove in both lateral and ventral portions, with seven neuromasts ( Fig. 7a ). Cephalic sensory system at supraorbital level open in continuous shallow groove, short and oblique, usually with vestigial lobes, with three neuromasts; whereas at supratemporal level open in curved groove, with three or four exposed neuromasts, without pronounced lobes, externally not connecting to postorbital canal ( Fig. 7b ). Mandibular canal in shallow open groove parallel to outer margin of lower jaw, with two small neuromasts ( Fig. 7c ).

Females: body depth, head depth and suborbital depth smaller than in males (body depth at pelvic-fin origin 21.4–22.9 % SL vs. 25.7–28.7; head depth 70 % HL vs. 72–78; suborbital depth 8–9 % HL vs. 10–14); caudal peduncle shallower than in males (caudal peduncle depth 13.0–13.1 % SL vs. 14.9–15.1; caudal peduncle length 179–185 as % of its depth vs. 139–147); base length of dorsal and anal fins smaller than in male (dorsal-fin base length 11.5–13.0 % SL vs. 13.1–15.1; anal-fin base length 13.9–15.4 % SL vs. 17.2–22.2).

Eggs slightly oval, measuring 2.0 mm long and 1.8 mm wide on average (n = 10).

Colouration. Distinct sexual dimorphism exposed in body and fin colouration.

Live male: illustrated in Figures 4–5 . Scales on trunk and caudal peduncle with pattern of vertically elongated iridescent light blue patches at scale centres, with dark grey to brown-grey scale margins along, and dorsally to, mid-longitudinal series, whereas scales of two to three series below with light brown to orange-brown scale margins, forming striped appearance of longitudinal lines on flank. Scales on dorsum above mid-longitudinal series with wider dark margin, resulting in progressively uniform dark grey appearance, whereas scales ventrally with progressively lighter scale centres and narrower margin, resulting in yellow to silver appearance on abdomen from opercle to pelvic fin.

Snout and dorsal portion of head dark grey, throat yellow to silver. Iris silver, with dark grey on anterior and posterior portions. Postorbital opercular region iridescent silver. Exposed branchiostegal membrane silver. Base of pectoral fin yellow. Reduced dark grey humeral blotch on post-opercular region. Dark grey vertical blotches on anterodorsal scales of mid-longitudinal series.

Median fins orange-brown proximally and medially, light grey distally, most specimens with narrow dark grey distal margin. Anal fin occasionally with light blue iridescence proximally close to base of fin. Pelvic fin light grey to orange-brown, with light blue iridescence proximally. Pectoral fin hyaline.

Live female: illustrated in Figure 6 , scales on trunk, dorsum and head light grey, lighter to silver on venter. Scales with dark grey-brown margin, creating reticulation on trunk. Scales with pattern of tiny iridescent light blue dots along two to three series below mid-longitudinal line on posteroventral portion of flank, creating reflective longitudinal stripes. Dark grey scale margins and dark grey patches on scales creating dark grey line along mid-longitudinal series. Scales on abdomen from opercle to pelvic fin white to silver, with light blue iridescence. Snout and dorsal portion of head dark grey to brown-grey, throat silver. Iris silver, with dark grey on anterior and posterior portions. Iridescent silver to light blue blotch on postorbital opercular region and iridescent yellow to silver humeral blotch on post-opercular region. Base of pectoral fin yellow. All fins hyaline.

Distribution. Lacustricola margaritatus is currently known from streams and swamps in the Lake Victoria basin in north-western Tanzania, south-western Kenya and southern Uganda, and in the Lake Kyoga basin in central Uganda ( Fig. 1 ). Known occurrences are restricted to the Lake Victoria ecoregion.

Ecology. Around Lake Victoria the landscape is characterised by flat-topped hills, about 1300 m asl, with forested valley sides, and papyrus swamps leading to swampy inlets at the lakeshore. The Lake Victoria and Lake Kyoga basins experience a bimodal rainfall pattern, with an annual precipitation of around 1250 to 1500 mm in the lakeshore region, but higher for the open lake, concentrated with two peaks during March-May and October-November with comparatively dry periods during December-February and June-July but without a harsh dry season ( Burgis & Symoens, 1987; Hughes & Hughes, 1992).

At the type locality, Lacustricola margaritatus was found together with Lacustricola bukobanus . At other sites, the accompanying fish fauna consisted of Clarias gariepinus Burchell , Ctenopoma muriei Boulenger , Enteromius apleurogramma Boulenger , E. lineomaculatus Boulenger , E. oligogrammus David , Haplochromis sp. , L. bukobanus , Micropanchax sp. , Nothobranchius robustus Ahl , N. ugandensis Wildekamp , Protopterus sp. , Pseudocrenilabrus multicolour victoriae Seegers , and the introduced species Poecilia reticulata Peters.

The type locality is a temporary pool formed on the floodplain of a small seasonal river in the Lake Victoria basin ( Fig. 8 ). The locality is situated about 7 km from where the river enters Lake Victoria. The habitat is an isolated pool in a shallow depression on the floodplain, directly adjacent to the riverbed, and formed primarily as a result of natural processes. At the time of collection of the type specimens, at the end of the rainy season, the habitat was a large and shallow pool more than 20 m long and about 10 m wide, with a maximum depth of 1 m, comprising part of a series of temporary marshes directly associated with the river. At the type locality, all collecting took place in the same general habitat. Aquatic vegetation comprised Nymphaea sp. , whereas the edge of the habitat was partially overgrown with grass. The water was turbid, the bottom of the pool was not visible. The water temperature around noon was 27.4° C, the pH was 7.8 and it contained 120 ppm of total dissolved solids. Water parameters, as measured by the authors at nine different sites throughout the range of distribution between 1999 and 2021, were as follows: temperature of 20.0–27.4° C; pH of 7.3–7.8; conductivity of 40–240 μS.

Conservation status. Lacustricola margaritatus is recommended to be listed as Least Concern, using the criteria of IUCN version 3.1 (2012). The known extent of occurrence (EOO) is 168,943 km ². Within its area of distribution, the species seems to be widespread in a range of several river drainages in the basins of Lake Victoria and Lake Kyoga, and it is known from more than 25 threat-based locations.

However, there is increasing habitat degradation due to expansion of agriculture and urbanisation in the area. The species inhabits freshwater wetlands, breeding in small and shallow, typically seasonal wetland habitats. Wetlands in the Lake Victoria basin have been progressively decreasing as a result of human activities ( Sayer et al., 2018). Some sites of known subpopulations of the species are situated adjacent to urban areas. The increasing pressure on land resources, with consequent habitat degradation, will impact the vulnerability of this species in terms of conservation status.

No conservation measures are in place for this species, and it is not known from any protected areas. There is a need for improved habitat protection at the locations where the species is known to occur. Further surveys aimed at investigating the entire range of distribution are needed to better determine the appropriate measures for conservation.

Biology. Aquarium maintenance of selected specimens was undertaken for observation of breeding behaviour and biology. Lacustricola margaritatus has a non-seasonal mode of reproduction, typical of the family. Eggs are deposited among floating or hanging vegetation. Under captive conditions, a synthetic mop was used successfully as a spawning medium. An embryonic development period of 12–14 days was observed at a temperature of about 22–24 °C. The relatively large eggs measure around 1.8–2.0 mm and the fry can consume Artemia nauplii after hatching. Under captive conditions sexual maturity is reached at an age of five to six months.

Etymology. The specific name margaritatus is a Latin participial adjective meaning “adorned with pearls”, referring to the striped colour pattern of distinct pearlescent patches along the longitudinal series on the side of body.

Figures

FIGURE 1. Map of the region around Lake Victoria and Lake Kyoga in eastern Africa, showing the distribution of Lacustricola margaritatus. T, type locality.

FIGURE 3. Lacustricola margaritatus, RMCA 2021.011.P.0001, holotype, male, 26.5 mm SL; Tanzania: Lake Victoria basin: ephemeral swamp about 3.5 km west of Kiziramiaga township.

FIGURE 4. Lacustricola margaritatus, RMCA 2021.011.P.0001, holotype, male, 26.5 mm SL, live; Tanzania: Lake Victoria basin: ephemeral swamp about 3.5 km west of Kiziramiaga township. Photographed after one month in captivity.

FIGURE 5. Lacustricola margaritatus, RMCA 2021.011.P.0006, paratype, male, 26.1 mm SL, live; Uganda: Lake Victoria basin: Lutembe Bay, east of Namulanda. Photographed after one month in captivity.

FIGURE 6. Lacustricola margaritatus, female, about 25 mm SL, live; Uganda: Lake Victoria basin: Lutembe Bay, east of Namulanda. Photographed after one month in captivity.

FIGURE 7. Diagrammatic representation of the cephalic sensory system in Lacustricola margaritatus; RMCA 2021.011. P.0001, holotype, male, 26.5 mm SL; a, lateral view of head; b, dorsal view of head; c, ventral view of head.

FIGURE 8. Type locality of Lacustricola margaritatus; Tanzania: Lake Victoria basin: ephemeral swamp about 3.5 km west of Kiziramiaga township. Photographed on 31 May 2019.