Sternarchella rex

description

Description. Largest known species of Sternarchella reaching an LEA of 405 mm. Pectoral fin size small, less than 80 % HL. PA % large, 44 - 66 % HL. Head wide, distance between lateral margins 46 - 64 % HL. Preorbital (snout) length moderate, 30 - 35 % HL. Postorbital distance large, 64 - 73 % HL. Eye diameter small, 5 - 7 % HL. Interorbital distance large, 18 - 27 % HL. Mouth wide, distance between ricti 22 - 32 % HL. Body depth equal or greater than HL. Body pale white with pinkish and metallic green sheen in living specimens. Scales absent on posterolateral portion of body. Scales large in size with 5 - 8 present above lateral line at mid-body. Scales dorsal to lateral line rhomboid at midbody. Rictus extends to a vertical with mental symphysis, gape very small, less than twice eye diameter. Oral aperture terminal, upper and lower jaws equal in length. Body cavity long, 15 - 16 pre-caudal vertebrae present. Proximal surface of first displaced hemal spine narrower then descending blade. One to two displaced hemal spines. Swim bladder not extending posterior to body cavity. Anal-fin pterygiophore length longer than hemal spines. Proximal anal-fin pterygiophores long, equal or long

Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species

description

Electric Organ Discharges. The ht-EODs of five of the type series were recorded (Fig. 14). The ht-EOD comprises a wave-type waveform with two peaks in each cycle. A dominant biphasic component is followed by a secondary peak of positive polarity (Fig. 14, left). The waveform dips to near the zero voltage baseline between the two peaks (in some cases exhibiting a constant (flat) low voltage, only slightly positive to the baseline) and crosses the baseline twice during the main biphasic component. The fundamental frequency varied in recorded specimens from 945 - 1096 Hz, mean 1023 Hz, standard deviation 54 Hz). The power spectral density computed from a Fast Fourier Transform (Fig. 14, right) exhibits a harmonic distribution of energy, as is typical for wave-type gymnotiform ht-EODs (Crampton, Albert, 2006). In all but one specimen the peak (dominant) frequency of the power spectral density corresponds not to the fundamental frequency, but to the first harmonic. In one specimen (1999 - 02 - 03 - 05), the peak frequency corresponded to the second harmonic. Although none of these specimens were in full reproductive condition, two were sexed as male (fundamental frequency 945 - 1096 Hz)

Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species

description

Figs. 11 - 12 a, Tab. 3 urn: lsid: zoobank. org: act: 67 F 5 A 55 F-A 093 - 4512 - 861 E- 0 B 53 A 27 CECCB

Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species

diagnosis

Diagnosis. Sternarchella rex can be diagnosed from all congeners by the following combination of characters: a wide head, HW 46 - 64 % HL (vs. 36 - 45 % HL in all other Sternarchella), a large interorbital distance, IO 18 - 27 % HL (vs. 11 - 22 % HL in S. calhamazon S. duccis, S. orinoco, S. orthos, S. patriciae, S. raptor, and S. schotti) (shared with S. sima), a deep body, depth greater than or equal to HL (vs. body depth less than HL in S. calhamazon, S. duccis, S. orinoco, S. orthos, S. patriciae, S. raptor, and S. schotti) (shared with S. sima), an ossified third basibranchial bone (vs. unossified in S. calhamazon, S. duccis, S. orinoco, S. orthos, S. patriciae, S. raptor, and S. sima) (shared with S. schotti) and anal-fin pterygiophores that are longer than hemal spines (vs. short anal-fin pterygiophores in S. duccis, S. orinoco, S. orthos, S. patriciae, S. raptor) (shared with S. calhamazon, S. patriciae, and S. schotti).

Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species