Bedotia leucopteron, Paul V. Loiselle & Damaris Rodriguez, 2007

Paul V. Loiselle & Damaris Rodriguez, 2007, A new species of Bedotia (Teleostei: Atherinomorpha: Bedotiidae) from the Rianila drainage of Eastern Madagascar, with redescriptions of Bedotia madagascariensis and Bedotia geayi., Zootaxa 1520, pp. 1-18 : 11-16

Bedotia leucopteron sp. nov. (Figure 6.)

Holotype: AMNH 231263. Sandrakatrana Stream at Ampasimbe Village, Toamasina Province, Madagascar (18o 56' 26S, 48o 41' 01 E). Altitude 126 m. Rianila drainage. Collected 21 October 2000 by villagers; single male specimen, 64.1 mm SL.

Paratypes: AMNH 231265. Same locality and collection data as holotype. Eleven specimens, 30.5-58.6 mm SL. MNHN 1942 0081. Beforona, Toamasina Province, Madagascar. Rianila drainage. Collected by R. Decary; 8 specimens, 56.5-71.9 mm SL.

Diagnosis

Living Bedotia leucopteron are readily distinguished from congeners by their metallic blue and gold base coloration, the presence of numerous small irregularly distributed black spots on the flanks rather than a pair of discrete black lateral stripes and the broad, iridescent white margins of the vertical fins in specimens> 25.0 mm SL. The distinctive melanophore pattern of the flanks, opaque white margins of the unpaired fins, deeper body and markedly posterior insertion of the second dorsal fin, as reflected by a snout to D2 distance of 66.2- 71.9 (mean: 68.5 ± 1.3) % SL are likewise diagnostic in preserved specimens.

Description

Morphological measurements and meristic counts are given in Table 4. Bedotia leucopteron can grow to 110.0 mm SL in captivity. The largest specimen examined in this study is a 64.1 mm SL male. Bedotia leucopteron is a robust fish somewhat deeper bodied than either of the two preceding species and showing a moderately curved ventral outline. Dorsal outline of head and nape moderately curved to first dorsal fin. Head length divisible 3.1-3.5 times in the standard length. First dorsal fin origin is posterior to the vertical through the pelvic fin insertion, while that of second is posterior to the vertical through the anal fin origin.

Snout slightly indented behind the premaxillary pedicels. Snout length divisible 3.1-4.0 in the head length. Lower jaw is slightly prognathous and angled at about 40°-45° to horizontal when mouth is closed.

Premaxilla and maxilla extend posterior to the anterior margin of the orbit. Premaxilla with a distinct lateral "Bedotia notch". Orbital diameter divisible 2.8-3.4 times in the head, 0.7-1.1 times in the snout length.

Teeth. Anteriorly both upper and lower jaws bear 4 to 6 rows of numerous small, strongly recurved unicuspid teeth. The outermost row of teeth is poorly differentiated from those of the inner band. The lower jaw and the premaxilla posterior to the Bedotia notch each have a single row of teeth. A single row of teeth is present along the anteroventral face of vomer. A small patch of endopterygoid teeth is present. No palatine or ectopterygoid teeth are present, at least in individuals of sizes available for examination.

Gill Rakers. Two or three stout hypobranchial rakers and 11-12 (mode: 11) elongate ceratobranchial rakers are present on the lower limb of the first branchial arch. All rakers are strongly denticulate.

Scales. Body is fully covered with large, regularly imbricate, cycloid scales. Predorsal scales along the dorsal midline: 14 or 15 (modal value: 15). Scales along the midlateral axis from just behind the operculum, above the pectoral fin, to the end of the hypural plate: 32-35 (mode: 34). Scales in transverse series between the anal fin and the second dorsal fin (including a very small scale adjacent to each fin): 9. Scales between the first and second dorsal fins: 2. Circumpeduncular scales: 10-12 (mode: 10). Dorsal, anal, and caudal scale sheaths and axillary pelvic scales are absent.

Fins. First dorsal fin with 4 weak spines. Second dorsal fin rays: 10-12 (mode: 11), the first 4 or 5 unbranched. Anal fin rays: 15-17 (mode: 17), the first 4 or 5 unbranched. High-set pectoral fins with 12-13 (mode: 12) rays, the longest extending well beyond the vertical to the pelvic fin insertion. Pelvic fins with one weak spine and five strongly bifurcate, branched rays. Caudal fin weakly emarginate.

Vertebrae. Total vertebral count taken from radiographs: 34-36 (mode: 35) and a terminal, hypural-bearing half centrum. Pre-caudal vertebrae: 18-19 (mode: 18). Caudal vertebrae: 16-17 (mode: 17).

Viscera and Diet. Gut extremely short, intestinal length only about one-third body length. Examination of feces produced by newly caught specimens within two to four hours of capture revealed the remains of both aquatic insect larvae and terrestrial insect imagos, suggesting that this species opportunistically exploits both autochthonous and allochthonous food sources.

Coloration

Living specimens: Figure 7 depicts a male, Figure 8 a female and Figure 9 juvenile B. leucopteron . These photographs do not show the narrow salmon pink mid-dorsal line in specimens> 25 mm TL. This species is not characterized by color polymorphism with respect to fin coloration.

Preserved specimens: Top of the head, dorsum and upper third of the flanks light brown, each scale with a darker brown margin. Flanks beige, shading to off-white on the venter. A grey band two scale rows wide extends along the midlateral line from the base of the caudal fin to a point just above the origin of the ventral fins. The posterior half of the flanks irregularly speckled with small black spots. The basal half of both dorsal fins and the anal fin clear grey, marked with black inter-radial streaks. Their distal half is opaque white. The median region of the caudal is clear grey marked with black inter-radial streaks, producing a triangular dark basal zone. The remainder of the caudal is opaque white. The ventral fins are opaque white, the pectorals hyaline.

Females differ from males in having clearer traces of the median and subpectoral lateral bands and fewer black dots on the posterior half of the flanks. The vertical fins are hyaline basally with dusky grey inter-radial streaks and narrower opaque white distal margins. Those of specimens> 50.0 mm SL may be irregularly sprinkled with small black dots. The ventrals and pectorals are hyaline.

Etymology

The species name, derived from the Greek leukos, white and pteron, fin, refers to the iridescent white fin coloration particularly evident in adult males. It is to be treated as a noun in apposition.

Range

The type series of Bedotia leucopteron was collected from the middle reaches of the Iaroka-Rianila basin. Further material has been collected at localities within this drainage situated along Route Nationale 2 between 100 m and 843 m above sea level (Figure 3). Additional collecting is required to ascertain whether it is present in adjacent drainages.

Natural History

All the streams from which B. leucopteron has been collected flow under degraded forest cover. As is the case with the preceding species, its occurrence is not influenced by the composition of the riparian vegetation. The Lazana River at Beforona flows strongly even during the driest month of the year and according to local residents, becomes torrential during the rainy season. Recurrent flooding has undercut the banks and caused many trees to fall into the river. Size-graded schools of fifty to one hundred B. leucopteron can be observed from its banks swimming through these tangles of waterlogged wood.

While their waters are very low in dissolved solids (GH: <17.1-35.0 ppm; electrical conductivity: 10.0- 21.0 μmho/cm2), pH values in these streams range from 6.0-7.0 and do not reach the extremes characteristic of coastal black water habitats. Water temperature in such habitats is strongly influenced by altitude. That of the Sahamamy River, the lowest altitude at which this species has been collected, measured 26° C, while values of 20° C. and 17° C respectively were measured in the Lazana River and in Amalabe Creek during the month of October. Residents of both Amalabe and Beforona stated that water temperatures of their respective streams did not vary noticeably on a seasonal basis. Nevertheless, October is early in the austral spring, so it is possible that summer temperatures in both streams are slightly warmer.

This species coexists with Gambusia holbrooki in Sandrakatrana Creek and Xiphoporus maculatus in the Sahamany River. According to local residents, Channa maculata also inhabits the quieter reaches of the latter stream. In the Lazana River, B. leucopteron shares its habitat with X. maculatus , an undescribed eleotrid of the genus Ratsirakia , the tadpoles of several frog species, diving beetles, a Macrobrachium species and a freshwater crab. The Amalabe Creek population occurs syntopically with two other bedotiids, Rheocles alaotrensis and an undescribed Rheocles species, the same Ratsirakia present in the Lazana River, and X. maculatus . According to local residents, eels are the only predatory fish present at these altitudes. Bedotia leucopteron is thus chiefly at risk from kingfishers and the skilfully wielded tandroho (woven reed baskets) of artisanal fisherfolk.

Conservation Status

Although Mantadia-Andasibe National Park affords the watershed of the of the Iaroka-Rianila basin a degree of protection, the middle reaches of this basin are characterized by much reduced and at best degraded forest cover. Nevertheless, B. leucopteron is quite abundant in those localities where it occurs. Like the preceding species, it does not appear at present to be seriously endangered, notwithstanding the presence of potentially competitive and/or predatory naturalized poeciliids throughout its altitudinal distribution and of the highly predatory Channa maculata at its lower end. It should be classified as vulnerable following the criteria established by the I.U.C.N.

Discussion

The lateral melanophore pattern of adult B. leucopteron somewhat resembles of that of Bedotia masoala Sparks 2001 , Bedotia marojejy Stiassny and Harrison 2000 and three undescribed congeners restricted respectively to the basins of the Sambava, Bemarivo and Mahanara du Nord Rivers in northeastern Madagascar. Its ontogeny in B. leucopteron , however, is quite different from that of the adult color pattern of this northern quintet of species, which for convenience sake we will refer to subsequently as the karikary group, from the Malagasy word for speckled. Juvenile B. leucopteron develop well-defined black lateral stripes within two weeks of hatching which become more intense until the young reach c. 30.0 mm SL. By this time, the stripes are more or less broadly edged in metallic gold. As the fish grow larger, the black lateral stripes begin to break up and the zone of metallic gold progressively expands while undergoing a comparable degree of fragmentation. The end result of this process is the distinctive adult color pattern seen in both sexes of B. leucopteron . In the three representatives of the karikary group bred to date, juveniles develop indistinct dusky lateral stripes shortly after hatching. In an attenuated form, these stripes persist into adulthood in females, but by the time males attain 3.0 cm SL, they have been replaced by a more or less well defined series of diffuse black spots, whose intensity and size decrease progressively as the fish grow larger.

The different fashion in which their superficially similar adult coloration develops in B. leucopteron and the species of the karikary group suggests that a spotted adult color pattern has evolved independently at least twice in the genus. This hypothesis is supported by the results of a recent genetic study of the Bedotiidae (Sparks and Smith, 2004), which recovers the karikary group as an assemblage of closely related species but places B. madagascariensis as the closest relative of B. leucopteron .