Lethrinops chilingali, Turner & Crampton & Genner, 2023

Turner, George F., Crampton, Denise A. & Genner, Martin J., 2023, A new species of Lethrinops (Cichliformes: Cichlidae) from a Lake Malawi satellite lake, believed to be extinct in the wild, Zootaxa 5318 (4), pp. 515-530 : 518-524

Lethrinops chilingali new species.

Holotype: BMNH 2023.1 .11.1, female, 70.9 mm SL, collected from seine catches, Lake Chilingali (12.94°S, 34.21°E), 22–24 June 2009.

Paratypes: BMNH 2023.1.11.2-21, twenty specimens 59.3–81.2 mm SL, collected with holotype .

Other material (excluded from the type series): BMNH 2023.1.11.22-28; seven specimens 56.8–98.7mm SL, laboratory bred from specimens collected at Lake Chilingali

Etymology: ‘chilingali’ from Lake Chilingali, the type locality, used as a noun in apposition.

Diagnosis: The outer tooth row of the lower jaw curves smoothly to end just behind the inner tooth rows ( Lethrinops - type dentition), distinguishing the species from other Lake Malawi haplochromines apart from species of the genera Ctenopharynx , Lethrinops , Taeniolethrinops or Tramitichromis . Lethrinops chilingali can be distinguished from other species in the genera Ctenopharynx , Lethrinops , Taeniolethrinops and Tramitichromis by the presence of a conspicuous horizontal series of dark grey to black spots along the middle of the flanks behind the head, linked to form one or two longer dashes, in total comprising 3–6 separate elements. Lethrinops lethrinus has a similar horizontal dark midlateral band, but it is typically more continuous, particularly posterior to the first anal spine, rather than broken into shorter spots and dashes. The horizontal melanic elements are generally not exhibited in dominant reproductively active males, however. L. chilingali also typically has a less ventrally placed mouth and shorter snout than L. lethrinus (snout as % of head length: 31.1–41.8 in L. chilingali , 37.6–50.0 in L. lethrinus ).

Description. Body measurements and counts are presented in Table 2. L . chilingali is a small (<85mm SL in wild-caught specimens) moderately laterally compressed (maximum body depth 2.0–2.4 times maximum head width) cichlid fish with a moderately long snout (31.1–41.8 % head length). Females and immature males have distinctive melanic markings in the form of a horizontal row of dark spots and dashes (fig. 3b, d) and also have a thin red dorsal fin margin, while mature males are brilliant metallic green with a red dorsal fin margin above broader black and white bands (fig. 3f).

All specimens are relatively deep-bodied and laterally compressed, with the deepest part of the body generally well behind the first dorsal fin spine. The anterior upper lateral profile is almost straight from the tip of the snout to the plane of the posterior margin of the eye, occasionally with a slight concavity above the eye, gentle sloping at an angle of about 40-degrees to the horizontal plane. There is no inflection to the angle of the profile above the eye (in contrast to Tramitichromis and Tropheops Trewavas 1984 ) and the premaxillary pedicel makes little or no interruption to the profile. The tip of the snout lies at about the same level in a horizontal plane as the upper margin of the insertion of the pectoral fin and at or below the level of the lowermost margin of the eye. The lower anterior lateral profile is also almost straight as far as the insertion of the pelvic fins, gently angled to the horizontal plane (about 12–15-degrees) and with little inflection at the posterior angle of the lower jaw even when the mouth is fully closed. The lower profile is more or less horizontal between the pelvic and anal fins. The mouth is relatively small and moderately upwardly-angled (gape about 40-degrees to horizontal). The caudal peduncle is relatively slender (1.4–1.8 times longer than deep). The pectoral fins are relatively long, extending past the first anal spine, but the pelvic fins are generally short of this, except in the largest mature males. The dorsal and anal fins, when folded, end well short of the caudal fin insertion, except in large mature males. The caudal fin is crescentic. The eye is large and circular and almost touches the upper lateral profile in perpendicular lateral view.

The flank scales are weakly ctenoid, with the ctenii becoming reduced dorsally, particularly anteriorly above the upper lateral line, where they transition into a cycloid state. The scales on the chest are relatively large and there is a gradual transition in size from the larger flank scales, as is typical in non-mbuna Lake Malawi endemic haplochromines ( Eccles & Trewavas 1989). A few small scales are scattered on the proximal part of the caudal fin.

The cephalic lateral line pores are inconspicuous and the flank lateral line shows the usual cichlid pattern of separate upper and lower portions. The lachrymal bone is about as wide as deep and the lateral line pores are heavily overgrown with skin.

The lower jaw is relatively small, with thin mandibular bones. The jaw teeth are small, short and erect. The outer series in both the upper and lower jaw are short, blunt, erect and largely unequally bicuspid. These is a single inner series of small, pointed tricuspid teeth.

The lower pharyngeal bone (fig. 4a) is small, lightly built, Y-shaped, and carries small, slender, widely-spaced simple teeth, as illustrated for L. lethrinus by Eccles & Lewis (1978, figure 5). The teeth gradually increase in size from lateral to medial positions, but there are no distinctly differentiated enlarged medial teeth. There are approximately nine teeth in the midline row and 17–18 on each side on the posterior row. The gill rakers are short and blunt, generally with the most anterior rakers in the lower and upper arches reduced to small stubs.

Female and immature fish (fig. 3d) are countershaded, pale sandy-brown dorsally, pale silvery on the flanks and underside. The flanks are marked by a midlateral horizontal row of dark spots and stripes extending from just behind the upper part of the operculum to the caudal peduncle. This varies between individuals, but generally comprises three to six separate melanic elements. A series up to six dark blotches is sometimes visible at the base of the dorsal fin, and element of a thin longitudinal dark stripe sometimes appears about half-way between the midlateral stripe and the base of the dorsal fin, usually starting a little behind the head and ending well before the caudal peduncle. The dorsal fin has a thin red outer margin and occasionally shows some faint dark spotting on both spinous and soft portions. Occasionally there is a pale submarginal band and anteriorly a thicker dark band. The caudal fin is usually translucent, sometimes with faint spotting. The anal fin sometimes shows a few faint yellowish spots.

Males in breeding dress (fig. 3f) are iridescent metallic green to pale blue. The horizontal melanic markings are occasionally exhibited when individuals are caught in fishing gear, or defeated in aggressive contests (seen in aquaria). Sometimes a series of faint dark vertical bars are visible. Patches of flank scales sometimes exhibit a metallic orange section anteriorly. The dorsal fin has a broad scarlet margin, underlain with a white submarginal band: these bands are narrower on the soft dorsal area. On the spinous dorsal, the red and white bands are underlain with a broad black band which extends to the base of the dorsal fin on the first inter-radial membrane, but as the membranes become longer posteriorly, the band overlies a series of orange spots extending onto the soft dorsal area, where they can be up to 10 spots between the longest rays. The membranes between the spots are pale grey to white. The caudal fin continues this pattern of orange spots with white/grey areas between. Sometimes the white inter-spot areas are missing, resulting in spots merging into stripes parallel to the fin rays. Occasionally, the white areas merge into stripes too. The upper and lower parts of the caudal fin can sometimes appear a bit darker, particularly on the basal section closer to the body, and particularly during dominant/courting behaviour. The pelvic fins are dark grey to black with a thin white anterior edge. The anal fin is greyish to black depending on mood, with a wide pink to red lower margin. A variable number (4–18) of large pale yellow ‘egg-spots’ are visible in one to two rows on the membranes behind the third anal spine. The colour of the iris varies from silvery to dark gold, with a darker spot above and below the lens continuing the line of a dark lachrymal stripe from the corner of the mouth. This stripe is very variable in intensity, showing up very prominently during territorial defence and courtship phases. The lower surface of the head and chest can turn dark grey during courtship and territorial behaviour but is otherwise pale greyish.

Distribution. Known only from Lake Chilingali in the Lake Malawi catchment (fig. 4b).

Behaviour and Ecology. The diet of L. chilingali specimens sampled in 2009 consisted largely of chaoborid (midge) larvae and pupae, along with cladocerans and other larger invertebrates, including odonatan nymphs and caridinid shrimps, but with little detritus, perhaps suggesting more midwater feeding than is usual in Lethrinops species. The behaviour of the species in the wild has not been observed, as the water of Lake Chilingali was highly turbid when visited between 2004 and 2009.

In captivity, L. chilingali females, non-territorial males and juveniles tend to aggregate in loose groups, feeding not only in the sediment, but on objects such as rocks or plants, or even at the surface. When attempts are made to catch the fish, they show a strong tendency to dive into the sand, turning sideways and completely burying themselves. This same behaviour has been reported to occur in the wild in Fossorochromis rostratus (Boulenger 1899) , another cichlid from the Lake Malawi radiation ( Fryer & Iles 1972, p. 207).

Dominant male L. chilingali are territorial and actively court females in typical haplochromine style: fins wide open, body horizontal or head-up, making rapid darts to the spawning site and back to the female, with spawning taking place amid bouts of circling and quivering, while alternating head-to-anal-fin ‘T-positions’ on the substrate. It is notable that dominant male coloration and aggression vary a lot, appearing to peak when females are approaching spawning, but are otherwise often quite subdued. During persistent bouts of courtship or aggression, the melanic elements of the male colour are emphasised, particularly the lachrymal/eye stripe, dark pelvic and anal fins, dark upper and lower margins of the caudal fin and even faint vertical barring on the flanks. Even in a large tank with a high density of fish, there is usually just a single dominant male: this is similar to Astatotilapia Pellegrin 1904 , which tend to be solitary breeders. Communal lek breeders, such as Oreochromis Günther 1889 will usually divide up a tank into numerous smaller territories and engage in frequent boundary disputes. This suggests that Lethrinops chilingali are not communal lek breeders in the wild.

There is little indication of bower construction in L. chilingali when a sand or gravel substrate is provided: dominant males usually try to lead females to a slight depression near to an object such as a rock or piece of wood: in a bare tank, the focus would probably be the tank bottom near one of the corners or a wall near a heater or filter inlet. This is in marked contrast to reports of L. lethrinus where complex bowers have been recorded in the field, out over open substrate ( Konings 2016, p. 369). In L. chilingali , the construction of the depression seems almost haphazard: males have not been observed to show consistent bouts of digging, but spend most of their time chasing, then returning to the territory focus next to the object, during which they make occasional ‘feeding movement’ of picking up a mouthful of substrate, moving forwards and ejecting it through the mouth and/or opercular openings at a slight distance away. This occurs all over the vicinity of the side of the object they are defending, but there seems to be a slight bias towards a certain point up against the object, which thereby becomes a shallow depression.

Female L. chilingali are maternal mouthbrooders, brooding young until they are capable of independent feeding. As fry complete the absorption of the yolk, they show through the female’s buccal membrane as a dark area, but females do not develop the ‘warpaint’ typical of fry guarders, such as known Astatotilapia or Oreochromis : dark eyes, lachrymal stripes and forehead stripes. There is no indication that females guard free-swimming fry or permit them to return to their mouths. This non-guarding behaviour is similar to other known shallow-water Lethrinops species.