Bedotia geayi Pellegrin 1907

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 : 8-11

Bedotia geayi Pellegrin 1907

Bedotia geayi Pellegrin 1907 : 205. Morafeno, dans les placers, à une altitude de 300 m environs, aux sources des ruisseaux de la Haute-Maha, affluent du Bas-Mananjary. (Morafeno, at approximately 300 m altitude, over sand bottoms at the sources of the headwaters of the Upper Maha, a tributary of the Lower Mananjary). Syntypes: MNHN 1907 35-37 (11).

Diagnosis

Bedotia geayi of both sexes can be distinguished from laterally striped congeners by the presence of a discrete black basal spot on the caudal fin base in both living and preserved specimens. Living males have red dorsal and anal fin margins and a red caudal fin, as well as a large red spot on the chin, while a narrow, more or less well defined black margin is present in the caudal fin of preserved individuals. Elevated second dorsal [11-14 (mode: 12)] and anal [17-19 (mode: 18)] ray counts are likewise diagnostic for preserved material. Morphometric characters that set this species apart from B. madagascariensis are presented in Table 3.

Description

Morphological measurements and meristic counts are given in Table 2. The largest specimen examined is a 74.0 mm SL male. Bedotia geayi are gracile, relatively long-bodied fishes somewhat deeper-bodied anteriorly and showing a rather straight ventral outline. Dorsal outline of head and nape moderately curved to first dorsal fin. Head length divisible 3.3-4.5 times in the standard length. First dorsal fin origin is posterior to the vertical through pelvic-fin insertion, while that of second is posterior to the vertical through the anal fin origin.

Snout slightly indented behind premaxillary pedicels. Snout length divisible 2.9-4.1 times in the head length. Lower jaw is slightly prognathous and angled at about 40°-45° to horizontal when mouth is closed. Premaxilla and maxilla reach the anterior margin of the orbit. Premaxilla with a distinct lateral " Bedotia notch". Orbital diameter divisible 2.88-3.77 in the head, 0.93-1.01 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. Small patches of endopterygoid teeth are also present. No ectopterygoid teeth present, at least in individuals of sizes available for examination.

Gill Rakers. Two or three stout hypobranchial rakers and 10-13 (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: 13-14 (mode: 14). Scales along the midlateral axis from just behind the operculum, above the pectoral fin, to the end of the hypural plate: 31-35 (modes: 32, 33). Scales in transverse series between the origins of the anal and the second dorsal fin (including a very small scale adjacent to each fin): 9. Scales separating the first and second dorsal fins: 3. Circumpeduncular scales: 12. Dorsal, anal, and caudal scale sheaths and axillary pelvic scales are absent.

Fins. First dorsal fin with 5 weak spines. Second dorsal fin rays: 11-14 (mode: 12), the first 4 or 5 unbranched. Anal fin rays 17-19 (mode: 18), 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: 34-37 (mode: 36), and a terminal, hypural-bearing half centrum. Pre-caudal vertebrae: 18-20 (mode: 19). Caudal vertebrae: 15-17 (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 terrestrial insects, suggesting that this species relies primarily upon allochthonous food sources.

Coloration

Living specimens: Figure 4 depicts a sexually quiescent male Bedotia geayi . It does not show the diagnostic large red spot on the chin. The pectorals are hyaline in both sexes, but the color pattern of the unpaired fins and ventrals is sexually dimorphic. Figure 5 depicts an adult female. The clear yellow halo surrounding the black spot at the base of the caudal is diagnostic. None of the populations to date sampled is characterized by polymorphism with regard to male fin coloration.

Preserved specimens: Color pattern of the body as in B. madagascariensis , but the midlateral stripe terminates in a distinct black spot on the base of the caudal fin. Both dorsal fins and ventrals clear grey in males, hyaline in females. Anal in males clear grey, often with a narrow black edging along its posterior half, entirely hyaline in females. Caudal uniform clear grey with a variably present narrow black distal margin in males, hyaline basally, clear grey distally in females.

Range

The eleven syntypes of B. geayi , measuring 48.0-74.0 mm SL, were collected from the Maha River, a north bank tributary of the Mananjary River near the town of Morafeno, at an altitude of c. 300 m. This species has also been collected from several south bank tributaries of the Mananjary (Figure 3).

Regrettably, neither preserved material of the Bedotia populations found between the Fanantara and Mangoro Rivers nor data on their life colors are available for analysis. This is unfortunate, as living individuals of B. geayi can be easily distinguished from B. madagascariensis by differences in the pigmentation of their unpaired fins noted in each species’ diagnosis while meristic and morphometric characters presented in Table 3 permit differentiation of preserved material. Until further sampling corrects this deficiency, the northern range limit of B. geayi cannot be precisely determined. In the Namorona River, the basin immediately to the south of the Manajary, B. geayi is replaced by an undescribed congener.

Natural History

Bedotia geayi inhabits small streams flowing under partial or complete forest cover at altitudes of 300 to 650 meters above sea level (Pellegrin, 1907; Reinthal and Stiassny, 1991). This species has not been collected from low altitude habitats in the Mananjary basin. This is may be due to the fact that the immediate hinterland of the town of Mananjary has undergone extensive anthropogenic modification. This process favors exotic species, which are better adapted to deal with increased silt loads and higher water temperatures that follow deforestation than are the majority of Madagascar’s native fishes.

Although the streams where it occurs frequently have a strong current, B. geayi prefers their well-shaded, quieter sections. Like the preceding species, it is indifferent to the composition of the riparian vegetation. This species has been observed swimming in loose, size-graded associations of up to a dozen individuals. Juveniles are usually found in the shallows, while adults frequent deeper water away from the banks. The scant information available on the natural history of B. geayi suggests that its dietary pattern, enemies and reproductive pattern are identical to those of B. madagascariensis .

Conservation Status

Bedotia geayi remains abundant in those localities where it does occur. While Channa maculata is present in the immediately adjacent Namorona basin, it has not to date been reported from that of the Mananjary. The presence of exotic poeciliids, notably the highly predatory Gambusia holbrooki , in the Manajary basin is presently a greater cause for concern. However, if for the moment B. geayi appears to be in no immediate danger of extirpation, its apparently circumscribed distribution suggests particular vulnerability to both further degradation of its habitat and the probable future translocation of C. maculata . Following the criteria established by the I.U.C.N., it should be considered a species of special concern whose status needs to be regularly monitored.