Pachypanchax sakaramyi (Holly, 1928)

Paul V. Loiselle, 2006, A review of the Malagasy Pachypanchax (Teleostei: Cyprinodontiformes, Aplocheilidae), with descriptions of four new species., Zootaxa 1366, pp. 1-44 : 14-19

Pachypanchax sakaramyi (Holly, 1928)

Panchax sakaramyi Holly, 1928 :313, Fig. 2 (type locality: “Ein Bach im Gebirge ca. 300 m hoch bei Sakaramy, 30 km landeinwärts von Diego Suarez auf Madagascar ” [= Sakaramy River, at village of Sakaramy, ca. 30 km south of Antsiranana (Diego Suarez) , 12°27'S, 49°16'E, 500 m. a. s. l.]). Syntypes: MSNM 56 [ex MSNM 4426 and NMW] (1); NMW 13463-13489 (16)) .

Diagnosis

Male P. sakaramyi differ from male P. playfairii , with which they have been conflated, in lacking raised dorsolateral squamation. Males also lack rows of discrete red dots on the flanks, red edging to the dorsal and anal fins, and a black caudal-fin margin. Their unpaired fins may instead be marked with black basal bands of variable width. Large female P. sakaramyi sometimes display a diffuse dusky basal zone in the dorsal fin, but lack the ocellated black basal marking present in the dorsal fin of female P. playfairii . Pachypanchax sakaramyi has the shortest dorsal fin base (10.7 ± 1.4% SL) of any Malagasy Pachypanchax , and further differs from all save one congener in having chest scales significantly smaller than those of the flanks. It differs from P. sparksorum sp. nov., which also possesses comparable pectoral squamation, in having a row of scales at the base of the dorsal and anal fins. Male P. sakaramyi differ further in their base color [yellow vs. blue], in having a shorter based dorsal fin and in their more rounded dorsal and anal fins. Female P. sakaramyi lack the reduced pattern of reddish-brown spots on the flanks characteristic of female P. sparksorum .

Description

Morphometric characters appear in Table 4. A Pachypanchax of moderate size, with a somewhat rounded snout. The mouth is wide, with the cleft directed upward. A single row of slightly recurved, conical teeth present in each jaw. Ten (13) or 11 (8) branchiospines on first gill arch. Two scale rows present on cheeks. Frontal squamation usually of E-type, with H scales present. In three of 18 specimens examined, the frontal squamation was of the G-type. Cephalic neuromast pattern open in 15 of 18 specimens examined, closed in the remainder. Scales cycloid, 31-32 (mode=31) along the midlateral line. 14-15 (mode=15) transverse scale rows immediately anterior to origin of anal fin; 20-22 (mode=22) scale rows around caudal peduncle. Deviations from modal values were observed only in aquarium-reared specimens. Scales on chest approximately one-third size of those on flanks. Vertebrae14 pre-caudal + 16 caudal.

Dorsal-fin origin above midpoint between origins of tenth and eleventh anal-fin rays. Dorsal-fin rays ii,9 (6); ii,10 (16); ii,11 (3). Sixth or seventh branched dorsal ray longest in both sexes. Anal fin rays ii,14 (9); ii,15 (10); ii,16 (14); iii,16 (7); ii,17 (4); iii,17 (5). Eleventh or twelfth anal ray longest in males, seventh or eighth ray longest in females. Longest ray in neither dorsal nor anal prolonged in either sex. Bases of dorsal and anal fins scaled. Caudal fin rounded truncate, the basal half to seven eighths heavily scaled. Pelvicfin rays i,5. Pectoral-fin rays 14-16 (mode=16).

Coloration

Living specimens: Figure 6 depicts a reproductively active captive-bred male from the Sakaramy River population. Figure 7 depicts a wild-caught female of the same provenance.

Preserved specimens (males): Dorsum, top of head, and lips dark brown. Dark gular bar absent. Upper half of flanks light brown anteriorly, shading to beige posteriorly. Scales on upper half of body narrowly edged in darker brown. Cheeks, opercula, throat, lower half of the flanks and venter yellowish-white. Dorsal and anal fins light brown. A narrow black basal band variably present on both fins. Caudal fin beige basally, shading to gray distally; a pattern of light brown interradial dots present basally; narrow black submarginal bands variably present along the upper and lower leading edges of fin. Ventral fins beige basally, shading to gray distally. Pectoral fins hyaline.

(Females): Coloration similar to males, but with an indistinct dark basal zone present on dorsal fin. All other fins hyaline.

Range

Pachypanchax sakaramyi was originally described (Holly, 1928) from specimens collected in the Sakaramy River, at the village of the same name (12°27'S, 49°16'E), ca. 30 km south of the city of Antsiranana [Diego Suarez], at 500 m above sea level. The Sakaramy is a tributary of the Sahakazoambany River, which flows into the Bay of Ambavarano at 12°26'S, 48°29'E. The only extant riverine populations of this species are restricted to a short stretch of the river between Ambohitra [Joffreville] and the village of Sakaramy, and to the upper reaches of the adjacent Antongombato River (Figure 5). Specimens in the collection of the MNHN, as well as data from interviews carried out in 1996 and 2001, suggest that P. sakaramyi was aboriginally present along the northern and eastern versant of the Ambohitra Massif, a Plio-Pleistocene volcanic formation that dominates the northern extremity of Madagascar, from the Antongombato River east and southwards to the headwaters of the Irodo River in the vicinity of the town of Anivorano. According to local informants, P. sakaramyi is still found in several low-altitude crater lakes, notably Farihy Texier and the nearby Farihy Fantany. Published reports to the contrary (Arnoult, 1959), this species does not occur in the Grand Lac, a high altitude crater lake situated to the west of the hydrographic divide, nor in any of the other highaltitude crater lakes located within the boundaries of Manokan’ Ambohitra [Montagne d’Ambre] National Park (Loiselle and Ferdenzi, 1997). De Rham (2000a, b) reports finding a population of superficially sakaramyi-like Pachypanchax in a westward-flowing stream on the southern piedmont of the Ambohitra Massif on the road between Bobasokoa and Anivorano, near the village of Andranotohiliny. The identity of this population remains to be verified, but should these fish prove to be P. sakaramyi the range of this species would comprise both slopes of the Ambohitra Massif.

Natural history

Pachypanchax sakaramyi inhabits high-gradient streams flowing under both degraded and intact forest cover and the peripheral waters of low-altitude crater lakes. Individuals of all sizes occur in both areas of strong current and tranquil pools, but are most abundant in the latter. Water temperatures between 20.5° and 22.2° C. were measured in partially shaded segments of the Sakaramy River in October. The water of the Sakaramy River and other streams draining the Ambohitra Massif is free of suspended matter, unstained by tannins, moderately soft (total and carbonate hardness 36.0-72.0 ppm), slightly alkaline (pH 7.2-7.5) and deficient in dissolved substances (conductivity 58.0-75.0 µS/cm2).

Stream bottoms range from bare bedrock to rounded basaltic cobble, interspersed with boulders up to 60 cm in diameter. Waterlogged branches are common along the margins of larger pools. No submerged aquatic plants were observed growing in the upper Sakaramy River, although a dwarf form of the umbrella papyrus, Cyperus alternifolius , does occur in small numbers wherever the stream margin is well illuminated. The Madagascar lace plant, Aponogeton madagascariensis , an unidentified epilithic Podostemonaceae and the exotic water hyacinth, Eichornia crassipes , were observed growing in P. sakaramyi habitat in the Antsahalalina River.

Pachypanchax sakaramyi has been observed feeding upon both stranded terrestrial insects at the surface of the water and upon small aquatic invertebrates taken from the bottom. As the upper Sakaramy River is devoid of other fish, its only enemies therein appear to be the Malagasy malachite kingfisher, and predatory invertebrates such as dragonfly nymphs and large prawns of the genus Macrobrachium . According to local informants, this species was formerly sufficiently abundant to be harvested for domestic consumption using tandroho (wicker fishing baskets).

Juvenile P. sakaramyi live in loose associations of up to a dozen individuals in the shallows. Adults frequent deeper water away from the banks. Large individuals of both sexes are solitary. Females tend to swim slowly in a stop-go manner, while males are in constant, active motion throughout their habitat. Territorial behavior was not observed, although courtship and spawning were. This suggests a consort-type mating system, in which males contend for access to ripe females rather than for control of spawning sites. No aggressive interactions were observed between males. However, as the fins of wildcaught males often show bite marks, bouts of serious fighting must occasionally occur.

Juveniles ranging in size from 1.0-3.0 cm TL were observed in both the Sakaramy and Antsahalalina rivers in 1994 and 1995. Based upon observations of the growth rate of juveniles in captivity, this size distribution suggests either a completely aseasonal reproductive pattern or a very protracted breeding season extending from early spring through the austral summer and into the autumn. Spawning was observed in October of 1995. The courting male assumes a position alongside and slightly to the rear of the female and attempts to maintain body contact while driving her towards a spawning site. Oviposition follows the typical cyprinodont pattern, with the pair assuming an S-curve, both sexes quivering intensely for a moment and the female then jerking abruptly away from the male. Multiple bouts can occur in rapid succession. Pairs were observed spawning upon waterlogged branches and among the cobbles of the stream bottom.

Conservation status

Pachypanchax sakaramyi has been extirpated from most of its aboriginal range since its description in 1928. Local residents ascribe its disappearance to predation by introduced Poecilia reticulata and Gambusia holbrooki upon P. sakaramyi fry. These observations are consistent with the known impact of introduced G. holbrooki upon populations of indigenous cyprinodontiform fishes elsewhere (Courtenay and Meffe, 1989; Galat and Robertson, 1992). A factor of equal importance is ongoing deforestation of the Ambohitra Massif, which changes the hydrological regime of small streams from permanent to intermittent, resulting in the extirpation of their populations of P. sakaramyi . The most recent loss of habitat was occasioned by the diversion of the source of the Sakaramy River in 2000 to provide drinking water for several private residences and the guesthouse of the Benedictine monastery located on the outskirts of Ambohitra. This has resulted in the virtual disappearance of the robust population of this species formerly present in the headwaters of the Sakaramy River (Loiselle and Ferdenzi, 1997). At present, substantial riverine populations of P. sakaramyi persist only in the stretch of the river between Ambohitra and the village of Sakaramy and in the headwaters of the adjacent Antongombato River (O. Lucanus, pers. com.).

Pachypanchax sakaramyi is thus classified as critically endangered, following the criteria established by the World Conservation Union (Raminosoa et al., 2002). A managed population has been established in North America and Europe, but barring the immediate implementation of an aggressive program of habitat protection and restoration, the extirpation of the remaining riverine populations appears inevitable.

Discussion

Arnoult (1959) regarded P. sakaramyi as a subspecies of P. playfairii , apparently on the basis of superficial similarity in overall facies and coloration. However, as noted in the Diagnosis, male P. sakaramyi lack the raised dorsolateral squamation of topotypical P. playfairii , and both sexes differ significantly from their Seychellois congener in details of coloration. The two taxa also manifest significant behavioral differences in captivity (Loiselle and Ferdenzi, 1997). Kiener (1963) apart, Arnoult’s assessment of its taxonomic status has not been accepted by subsequent workers, who have continued to afford P. sakaramyi full specific rank (Scheel, 1968; Parenti, 1981; Lazarra, 1984). Subsequent genetic studies have confirmed the distinctiveness of these two taxa at the species level (Collier, pers. com.).