Bedotia madagascariensis Regan 1903

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 : 2-7

Bedotia madagascariensis Regan 1903

Bedotia madagascariensis Regan 1903 : 416, pl. 14, fig. 2. Madagascar, eau douce. (Madagascar, fresh water). Holotype: MHNG 0665.007.

Diagnosis

Bedotia madagascariensis belongs to the group of species whose color pattern in life is based upon two dark lateral stripes clearly expressed in both sexes. This feature unambiguously distinguishes it from congeners in which the lateral stripes are either replaced by a pattern of dark spots or are altogether lacking in one or both sexes. It is readily distinguished from its laterally stripped congeners by its caudal fin coloration, which consist of an extensive hyaline to iridescent yellow-white basal zone, a crescent-shaped black median band and broad red or white tips. Low second dorsal [10-12 (mode: 11)] and anal [14-17 (mode: 16)] fin ray counts are diagnostic for preserved specimens. Morphometric features that distinguish this species from B. geayi are presented in Table 3.

Description

Morphological measurements and meristic counts are given in Table 1. Although Bedotia madagascariensis can grow to 100 mm SL in captivity, largest specimen examined in this study is a 85.9 mm SL male. This is a robust, relatively long-bodied species somewhat deeper-bodied anteriorly and showing a moderately curved ventral outline. Dorsal outline of head and nape moderately curved to first dorsal fin. Head length divisible 3.1-4.4 times in the standard length. First dorsal origin is posterior to the vertical through the pelvic fin insertion, while that of the second dorsal is posterior to the vertical through the anal fin origin.

Snout is slightly indented behind the premaxillary pedicels. Snout length divisible 2.9-3.4 times in the head length. Lower jaw is moderately prognathous and angled at about 35°-40° to horizontal when mouth is closed. Premaxilla and maxilla reach the anterior margin of the orbit. Premaxilla with the distinct lateral "Bedotia notch" characteristic of the genus (Stiassny, 1990). Orbital diameter divisible 2.9-3.8 times in the head, 1.0-1.1 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 the vomer. Small patches of teeth are present on the endopterygoid. No ectopterygoid teeth present, at least in individuals of sizes available for examination.

Gill rakers. Two or three stout hypobranchial rakers and 9-13 (mode: 10) 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 15-16 (mode: 15). Scales along the midlateral axis from just behind the operculum, above the pectoral fin, to the end of the hypural plate: 33-35 (mode: 34). Scales in transverse series between the origins of the anal and the second dorsal fins (including a very small scale adjacent to each fin) 9-10 (mode: 9). Scales separating the first and second dorsal fins: 3-4. Circumpeduncular scales: 12. Dorsal, anal, and caudal scale sheaths and axillary pelvic scales are absent.

Fins. First dorsal fin with 4-5 (mode: 4) weak spines. Second dorsal fin rays: 10-12 (mode: 11), the first 4 or 5 unbranched. Anal fin rays: 14-17 (mode: 16), usually the first 3 or 4 unbranched. Pectoral fins short, high-set with 12 rays, the longest barely reaching the vertical from 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 terminal, hypural-bearing half centrum. Precaudal vertebrae: 17-19 (mode: 19). Caudal vertebrae: 16-18 (mode: 16).

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 terrestrial insects, suggesting that this species exploits primarily allochthonous food sources.

Coloration

Living specimens: Figure 1 depicts a young pair of captive-bred B. madagascariensis descended from founders collected at Ambila-Lemaitso. The sexually dimorphic color pattern of the fins is clearly evident. All populations studied to date are characterized by male polymorphism with regard to the coloration of the unpaired fins. Their usual coloration is based upon discrete zones of red, yellow and black. First dorsal fin and ventral fins dusky distally, hyaline to metallic golden yellow basally. Second dorsal is metallic golden yellow basally, with a dark red margin and broad black submarginal band. Anal fin similarly colored, but a metallic golden yellow zone is sandwiched between a narrow black basal and a broader black submarginal band. The extension of the black midlateral band at the caudal base surrounded by an iridescent silvery white to metallic golden yellow halo, bordered in turn by a broad sooty black crescent-shaped band. Upper and lower distal caudal margins either dark red or iridescent white. However, the vertical fins of some males are uniformly red and black, or the yellow coloration is replaced by iridescent white. Within a given population, the representation of each color morph can vary from one year to the next.

In females, first dorsal fin dusky distally, clear yellow basally. Second dorsal whitish yellow basally, with an iridescent white margin and broad black submarginal band. Anal fin is similarly colored, but the lighter zone is sandwiched between narrow black basal and submarginal bands. The extension of the black midlateral band at the base of the caudal surrounded by a hyaline halo, bordered in turn by a broad sooty black crescentshaped band. The upper and lower distal margins of the caudal clear yellow shading to iridescent white.

The pectorals of males are hyaline with a dark spot on their distal tip, those of females uniformly hyaline.

Preserved specimens: The holotype of B. madagascariensis retains little of the species-typical melanophore pattern (Figure 2.). Dorsum warm brown shading to pale beige on the flanks and white on the venter. Top of the head warm brown, shading to beige on the cheeks and operculum. A narrow dark stripe extends from the tip of the snout to the angle of the operculum. Here it becomes a midlateral stripe two scale rows deep that extends from the margin of the operculum to the caudal peduncle and is a more diffuse form, extends onto the caudal fin for about half its length. The midlateral stripe is sometimes interrupted along its posterior third. The lower dark lateral stripe is usually evident only in recently preserved material. In males, first dorsal and ventrals are uniform clear grey, second dorsal and anal clear grey basally, hyaline distally, with narrow black basal stripes and variably expressed black submarginal stripes. In females, dorsal and anal fins uniformly hyaline. Caudal hyaline in both sexes, marked with a black crescent-shaped marking medially that is narrower and less intense in females.

Range

The type of B. madagascariensis , a single specimen 90.0 mm TL, was donated to the Museum of Natural History in Geneva by a Swiss visitor to Madagascar. In the original description (Regan, 1907), the type locality of this species is given only as "Madagascar; eau douce.". In a subsequent paper, Regan (1920) identified a series of specimens from Lac Rasoabe, next to the last lake of the series extending southward from Toamasina (Tamatave) to Andovoranto, at the mouth of the Rianila River, as B. madagascariensis . Prior to the completion of the railroad connecting Toamasina to Antananarivo, the initial stage of this journey entailed travelling by boat for several days along the Lakendrano Mpangalana (Pangalanes Canal) from Toamasina to the town of Andovoranto, thence up the Iaroka River to the head of navigation at Maromby. Such an itinerary would have afforded ample opportunity to secure specimens by either capture or purchase, for Bedotia remain abundant in this region of Madagascar and are still marketed for human consumption. As B. madagascariensis is replaced by the very differently colored Bedotia leucopteron sp. nov. in the middle reaches of the IarokaRianila drainage, the type material of this species could only have come from one of the many small streams flowing into this interconnected series of large coastal lakes.

The present range of B. madagascariensis extends from the lower reaches of the Ivoloina River, the effective northern terminus of the Lakendrano Mpangalana, at least as far south as Manambolo Creek, which drains into the Lakendrano Mpangalana 10 km south of the town of Vatomandry (Figure 3.). South of this point and in the middle and upper reaches of the Ivoloina River, B. madagascariensis is replaced by undescribed congeners. In the rivers to the north of the Ivoloina River, it is replaced by Bedotia longianalis Pellegrin, 1914 .

In the 1950's, this species was translocated to marshes near the village of Mahitsy, just outside of Antananarivo in the upper reaches of the westward-draining Betsiboka River (Kiener, 1963). The exercise was successful and the translocated fish bred freely. The recent capture of juvenile B. madagascariensis in the rapids of the Ikopa River near the village of Antanimbary and of adult fish in Lanefitra Creek at Ankadibe Village, several hundred kilometers to the west, suggests that this species is now widely established in the Betsiboka basin.

Natural History

Within its aboriginal range, Bedotia madagascariensis inhabits clear streams flowing under partial or complete forest cover at altitudes up to 30 meters above sea level. As long as the stream is shaded, this species appears indifferent to the composition of the riparian vegetation, prospering even when it is comprised entirely of exotic species. Although capable of breasting a fairly strong current, B. madagascariensis prefers the quieter sections of well-shaded streams. Rivers draining the eastern versant of Madagascar are characterized by extremely soft water (General hardness [GH]:<17.1 ppm, electrical conductivity 17.0-27.0 μmho/ cm2). It is thus not unusual to find this species inhabiting classic black water habitats such as Dracaena / Pandanus swamps, where pH values can be as low as 4.8. Although salinity levels up to 5.0 parts per thousand are tolerated in captivity, B. madagascariensis does not enter brackish water in nature. Water temperatures measured during the month of October in the habitats it frequents ranged from 23°-32° C.

Bedotia madagascariensis is typically observed in loose, size-graded associations of up to several dozen individuals. Juveniles are usually found in the shallows, while adults frequent deeper water away from the banks. There are no published data on the reproductive behavior of this species in nature. Collections made in October, towards the end of the dry season, include juvenile fishes as small as 2.0 cm TL. Taken with what is known of its growth rate in captivity, this suggests that B. madagascariensis enjoys a protracted breeding season in nature.

Prior to the introduction in the early 1970's of the spotted snakehead, Channa maculata , the only fish large enough to prey upon B. madagascariensis were cichlids of the genus Paratilapia , flagtails of the genus Kuhlia , the endemic grunter Mesopristes elongatus , Glossogobius giuris , and eels of the genus Anguilla . This species is also vulnerable to piscivorous wading birds and the Malagasy malachite kingfisher, Corythornis vintsioides . Despite its relatively small size, there is an active artisanal fishery for B. madagascariensis over most of its range. In captivity, individuals of this species can live for up to ten years. Predation pressure in all probability precludes comparable longevity in nature.

Conservation Status

A popular ornamental fish, B. madagascariensis is globally a low-risk species. Indeed, the number of individuals produced annually for the aquarium trade by commercial breeders in the Far East may well equal the number living in the wild. Although local informants consistently indicate that B. madagascariensis is less abundant than formerly, this species does not appear to be seriously endangered in nature. While Bedotia are usually considered to be forest-dependant fishes (Pellegrin, 1933; Arnoult, 1959; Kiener, 1963) B. madagascariensis has managed to cope well with the elimination of primary forest over much of its range. It is perhaps more accurate to describe this and other bedotiids as shade rather than forest dependant. This explains their persistence in streams where the riparian vegetation consists entirely of such exotic species as torch ginger, banana, lantana and Chinese bamboo. In unshaded or extremely turbid streams, this species is replaced by the naturalized poeciliids Gambusia holbrooki and Xiphophorus maculatus .

The chief threats to the survival of this species in the wild are the ongoing progressive degradation of its habitat, with concomitant risk of increased silt loading due to erosion and the inexorable spread of C. maculata . Unlike native piscivores, this exotic predator is not deterred by shallow water. Small streams thus afford B. madagascariensis no protection from its depredations, although the snakehead’s dislike of rapidly flowing water affords those native fishes capable of coping with a pronounced current at least a partial refuge. Following the criteria established by the I.U.C.N., wild populations should be classified as vulnerable.

Discussion

In 1953, Arnoult shipped live Bedotia collected from the town of Ambila-Lemaitso to France. This town is located on the shore of Lake Anjanaborona, which lies immediately to the south of Lake Rasoabe. They were introduced to the aquarium hobby under the name Bedotia geayi , notwithstanding the fact that the type series of B. geayi was collected from the Mananjary basin, several hundred kilometers to the south of Lake Rasoabe. The color pattern of male Bedotia recently collected from the Mananjary drainage differs significantly from that of Arnoult’s fish in lacking a black submarginal zone in the caudal fin and in the absence of yellow pigmentation in the dorsal and anal fins. Nor do the Manajary Bedotia display the red/white color polymorphism characteristic of the unpaired fins in B. madagascariensis . The two also differ with respect to a number of morphometric and merisitic characteristics (Table 3). We thus recognize the two taxa as specifically distinct and B. madagascariensis as the correct name for the species long sold as B. geayi in the aquarium trade.