Stomatorhinus ivindoensis

Stomatorhinus ivindoensis Sullivan & Hopkins, 2005

Languages: English

Overview

General Description

Stomatorhinus ivindoensis is recognized by the combination of the following characteristics:  (1) very small adult size (specimens larger than 56 mm SL never observed) with most adults between 35 and 48 mm SL; (2) caudal peduncle of moderate  width (caudal peduncle depth 37–45% of caudal penduncle length); (3) a small eye, 6.7– 10% of HL; (4) 8 to 9 pectoral rays and 14 to 17 dorsal fin rays; (5) first 22 to 28 scales along lateral line bearing pores, last pore-bearing scale lying posterior to a vertical through origin of anal fin, but positioned well in advance of caudal peduncle; (6) lobes of the caudal fin broad and rounded, without distinct points at apices.

This is a very small Stomatorhinus not known to surpass 56 mm SL. Mouth small. No submental swelling. Eye small, covered by epidermis. Inter-orbital distance is 72–90% of head width. Nostrils well separated with posterior nostril located near rictus of mouth. Teeth 7–8/8–9, usually 7/8, bicuspid. Head (including eye), upper back and belly covered by epidermis that is translucent in life, semi-opaque in preservation. When pressed to side, tip of pectoral fin extends well past origin of pelvic fin. Pectoral fin has 8 or 9 rays. Dorsal and anal fins roughly symmetrical above and below body axis, the anal fin (of 19–21 rays) slightly longer, with the dorsal fin (of 14–17 rays) originating at vertical through the origin of the fourth or fifth anal fin ray; the origins of the last dorsal and last anal fin rays at roughly the same vertical. Lobes of caudal fin short, very rounded and blunt. Caudal peduncle relatively short (14–16.5% of SL), of moderate depth (37–45% of length), with 12 circumpeduncular scales. First 22–28 scales along lateral line bearing pores, last pore-bearing scale lying past vertical through origin of anal fin. Total scales along longitudinal line 44–50. Scale rows between origin of pelvic fin and lateral line scale 11 to 13. Total vertebrae 36 (excluding urostyle). 

In life, specimens are uniformly dark chocolate brown, with little patterning in pigment along the body. Fins are translucent with dark brown pigmented rays. In alcohol, thick epidermis overlying head (including eye), upper back and belly appears opaque.

Author(s): Sullivan, John P.
Rights holder(s): Sullivan, John P.

Conservation

Conservation status

This species is locally abundant in the Ivindo River of Gabon near Makokou.  The proposed dam at Kongou Falls may impact this species and other Ivindo River endemic fishes.

Author(s): Sullivan, John P.
Rights holder(s): Sullivan, John P.

Description

Electric Organ Discharge

Stomatorhinus ivindoensis has a 110 to 720 microsecond duration EOD waveform with three to four peaks in the discharge (see Sullivan & Hopkins 2005, Fig. 5A–F). The EOD begins with a small head-negative phase or peak, P0, followed by a larger head-positive phase, P1, followed by the largest head-negative peak, P2. In some fish, the discharge ends with a final head-positive phase, P3. The peak spectral frequency of the Fourier Transform of the EOD is between 4000 Hz and 16,000 Hz. The EOD is sexually dimorphic among sexually mature individuals. Juvenile male EODs are similar to female EODs. Male EODs are longer in duration and have lower FFT peaks than females. They also differ in the heights of peaks P0 and P1 relative to the full peak to peak height compared to females. The EOD of a juvenile of this species was reported by Heymer & Harder (1975).

Author(s): Sullivan, John P.
Rights holder(s): Sullivan, John P.

Behavior

Author(s): Sullivan, John P.
Rights holder(s): Sullivan, John P.

Ecology and Distribution

Distribution

All known populations of this species are witin the Ivindo River basin of Gabon.

Author(s): Sullivan, John P.
Rights holder(s): Sullivan, John P.

Ecology

Individuals are usually found along the margin of small forest streams in root tangle where it occurs with other species of mormyrids, but has also been taken along the margin of the Ivindo River proper in deep water. Individuals are often found spaced apart at intervals of 50 cm to one meter.

Diet of this species has not been studied, but is probably similar to that reported for S. polli Matthes 1964 in which stomach contents were dominated by small crustaceans and insect larvae.

Author(s): Sullivan, John P.
Rights holder(s): Sullivan, John P.

Relevance

Local Names

mebio (Kwele)

Author(s): Sullivan, John P.
Rights holder(s): Sullivan, John P.

References

Hopkins, C. D., Lavoué S., & Sullivan J. P. (2007).  12. Mormyridae. (StiassnyM L J., TeugelsG G., HopkinsC D., Ed.).The Fresh and Brackish Water Fishes of Lower Guinea, West-Central Africa. 1, 220–334.
 
Sullivan, J. P., & Hopkins C. D. (2005).  A new Stomatorhinus (Osteoglossomorpha: Mormyridae) from the Ivindo River, Gabon, West Central Africa. Zootaxa. 847, 1-23.
 
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