Comprehensive DescriptionRead full entry
Pachypanchax arnoultisp. nov.
Holotype : AMNH 235862 (male, 58.8 mm SL), F2 descendant of fish collected from a Pandanus-Dracaena swamp draining into a tributary stream of the Ikopa River, flowing parallel to RN-4 at Antanimbary Village ( 17°10'79”S , 46°50'97”E ), 246 m a.s.l. (Betsiboka River drainage), P. V. Loiselle, R. Haeffner and J. Davidson , 7 Oct. 1997 .
Paratypes : AMNH 229576 (7, 43.2-55.1 mm SL), paratopotypes , from same stock as holotype . AMNH 229575 (5, 27.2-36.9 mm SL), Boinakely River, immediately below bridge on RN-4 ( 16°51'49”S , 46°57'80”E ), 153 m a.s.l. (Betsiboka River drainage), P. V. Loiselle , R. Haeffner and J. Davidson , 8 Oct. 1997 . MNHN 1928 0297 (5, 23.0-35.7 mm SL), Namahota River at Namoroka Village ( 16°24'S , 45°17'E ) (Andranomavo River drainage), G. Petit . MNHN 1963 0173 (7, 24.3-58.2 mm SL), Ampijoroa (Betsiboka drainage) , J. Arnoult .
The absence of raised dorsolateral scales and red lateral spots in males and of an ocellated black basal spot in the dorsal of females preclude confusion of this species with P. playfairii . It differs from P. sakaramyi and P. sparksorumsp. nov. in lacking reduced pectoral squamation. Pachypanchax arnoulti has the longest head (30.2 ± 1.8% SL) of any Malagasy Pachypanchax ZBK . This feature, together with lack of red coloration on the body and fins, distinguishes it from P. patriciae and P. varatraza . The combination of more rounded dorsal and anal fins, a longer caudal peduncle (17.0 ± 1.9% SL vs. 14.7 ± 1.6% SL), absence of rows of discrete metallic lateral spots and the presence of a narrow iridescent white margin along the anal and lower edge of the caudal in males set it apart from P. omalonotus .
Morphometric characters are given in Table 8. A Pachypanchax ZBK of moderate size with a distinctly pointed snout. The mouth is wide, cleft directed upward. A single row of slightly recurved, conical teeth present in each jaw. Nine (1), 10 (11) or 11 (15) branchiospines on the first gill arch. Two (11) or 3 (15) scale rows present on the cheeks. Frontal squamation of E-type, with H scales present. Cephalic neuromast pattern closed in three specimens in the type series, open in the remaining 22 and in all the additional material examined. Scales cycloid, 29-33 (modes=30-31) along the midlateral line. Fourteen or 15 (mode=14) transverse scale rows immediately anterior to origin of anal fin; 16-20 (mode=18) scale rows around caudal peduncle. Scales on chest same size as those on flanks. Vertebrae 14 pre-caudal + 17 caudal.
Dorsal fin origin above midpoint between origins of fifth and sixth anal-fin rays. Dorsal fin rays iii,8 (6); ii,9 (1); iii,9 (2); ii,10 (11); iii,10 (1); ii,11 (4); iii,11 (1); ii,12 (5). Seventh or eighth branched dorsal ray longest in both sexes. Anal-fin rays iii,12 (2); iii,13 (3); ii,14 (1); iii,14 (7); ii,15 (5); iii,15 (3); ii,16 (5); ii,17 (5). Twelfth or thirteenth anal ray longest in males, seventh or eight longest in females. Base of dorsal and anal fins scaled. Caudal fin rounded truncate, basal two-thirds to three-quarters heavily scaled. Pelvic-fin rays i,5. Pectoral-fin rays 14-16 (mode=16).
Living specimens: Figures 17 and 18 depict, respectively, an adult male and adult female of P. arnoulti . As they age, individuals of the topotypical population of P arnoulti sometimes develop amelanic patches on the dorsum. These appear as irregular areas of coppery or brassy pigmentation. These aberrant phenotypes occur more frequently in captivity than in the wild, possibly because such wild heteromelanic individuals are more vulnerable to avian predation.
Preserved specimens (Males): Dorsum, upper half of head, lips, and upper third of flanks brown, shading to beige on cheeks, operculum, throat, lower two-thirds of flanks, and venter. Scales of dorsum and upper two-thirds of flanks narrowly edged in dark brown. A pattern of faint, narrow, irregular dark vertical lines present on posterior half of body. Dorsal area gray, narrowly edged anteriorly with opaque white. Caudal fin gray, marked with a pattern of darker inter-radial dots basally and a narrow opaque white margin. Anal fin clear gray, narrowly edged with opaque white and marked basally with light blotches. Pelvic fins clear gray, with a darker leading edge. Pectoral fins hyaline. (Females): As in males, but without dark lines on flanks. All fins hyaline.
The species name honors Jacques Arnoult, in recognition of his many contributions to Malagasy ichthyology, and who first introduced this and other fishes from Madagascar to science and to the aquarium hobby in the 1950's.
Pachypanchax arnoulti is native to the basins of the Mahavavy du Sud and the Betsiboka, to the small independent streams that flow into the Mozambique Channel between the estuaries of the Betsiboka and Mahavavy du Sud, and to Lake Kinkony and its satellite lakes (Figure 19). It has also been collected from a hill stream draining the Tampoketsa highlands, which crosses the Antananarivo-Maevatanana road at the Kilometre 240 marker, 53 km east of the town of Maevatanana, and from the upper Kamoro drainage (P. de Rham, pers. com.). Its presence in the Mahajamba drainage, which lies to the north of the Betsiboka and is connected to it by the Kamoro, is probable but has yet to be confirmed. It is replaced in the Sofia River basin by an undescribed congener. Reports of this species from the Soahany drainage near the town of Antsalova, south of the Mahavavy du Sud (de Rham, 2000a), require confirmation.
This species, like P. patriciae , has been collected from a wide range of habitats. The type locality is a Pandanus-Dracaena swamp, whose waters are clear, tannin stained, acidic (pH of 6.2), soft (total hardness <17.1 ppm), and deficient in dissolved substances (electrical conductivity 16 μS/cm2). Neither filamentous algae nor vascular aquatic plants were present. Xiphophorus hellerii ZBK was also collected from the swamp’s outflowing stream, but P. arnoulti was the only species present in the swamp proper, which did supports a diverse assemblage of aquatic Coleoptera and Hemiptera.
This species was also collected in a small creek flowing into the Akalimolitra River, a tributary of the Betsiboka, and was observed in the shallows of the main channel of the Akalimolitra proper. Its waters were clear, colorless, with a neutral pH, moderate hardness (total hardness 68.4 ppm), and deficient in dissolved substances (electrical conductivity 34 μS/cm2). Neither filamentous algae nor vascular aquatic plants were present in either the main channel of the Akalimolitra or its tributary. Only P. arnoulti and dragonfly nymphs were collected from this creek, but, in the main channel of the Akalimolitra, this species occurs syntopically with Paretroplus kieneri ZBK , P. tsimoly ZBK , Oreochromis mossambicus , Glossogobius giuris and Awaous macrorhynchus .
Feces of freshly captured specimens contained recognizable remains of both the imagos of terrestrial insects and the nymphs and larvae of aquatic insects. Although this species is at risk from such piscivorous fishes as G. giuris , its most important predators in most habitats appear to be fish-eating birds and dragonfly nymphs.
Specimens collected in late October began spawning within a week after their arrival in the United States in early November. Observations of the growth rate of juveniles in captivity taken with the size distribution of specimens from the type locality suggest a protracted breeding season lasting through the austral summer.
The conservation status of P. arnoulti varies over its extensive range. During the past fifty years, its numbers have declined significantly within the Betsiboka-Ikopa drainage. Recent efforts to recollect this species from streams near the town of Maevatanana, where Arnoult (1955) found it to be abundant, were unsuccessful. These localities now are home to substantial populations of naturalized Xiphophorus hellerii ZBK . This species has also become very rare in the Ampijoroa Forest Reserve, where Arnoult collected a large series of specimens in the 1960's (J. S. Sparks, pers. com.), and appears to be under significant pressure from X. hellerii ZBK at the type locality and from G. holbrooki ZBK in the lower reaches of the Kamoro (P. deRham, pers. com.). However, it remains abundant in both the upper Kamoro River and in the small streams situated between the mouths of the Betsiboka and Mahavavy du Sud (P. de Rham., pers. com.), as well as in satellite lakes of the Kinkony basin in the delta of the Mahavavy du Sud (N. Raminosoa, pers. com.). Following the criteria established by the World Conservation Union (Raminosoa et al., 2002), P. arnoulti is thus classified as a species of special concern, whose status needs to be monitored on a regular basis.
Most literature published since 1950 purporting to deal with various aspects of the biology of P. omalonotus (Arnoult, 1955, 1959; Kiener, 1963; Kiener and Thérezien , 1963; Scheel, 1968; Parenti, 1981; Lazarra, 1984) actually refers to this species.