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| Microsternarchus javieri Cox Fernandes, Escamilla Pinilla, Alves-Gomes, in Escamilla Pinilla, Cox Fernandes et Alves-Gomes, 2025. |
ABSTRACT
Here we describe a new hypopomid species, Microsternarchus javieri n. sp., encountered in flooded savanna streams of the Branco River and in terra-firme streams in the mid- and lower portions of the Negro River basin. We compared this new species with M. bilineatus from the San Bartolo River, Venezuela, and M. brevis from the upper portion of the Negro River. We also compared this new species with two recently described species in the genus Microsternarchus, M. longicaudatus and M. schonmanni. We examined morphometrics, anatomical characters, DNA barcode distances for the COI (cytochrome C oxidase subunit I) gene, and electric organ discharge (EOD) parameters. We diagnosed M. javieri n.sp. based on variation in maximum body depth, eye diameter, caudal vertebral counts, number of anal fin rays, and the shape of the maxillae. The average intra-specific genetic distance (K2P) in M. javieri n.sp. was 0.83%, whereas the average inter-specific genetic distance to M. brevis was 12.45%, and to other hypopomids ranged from 17.21 to 21.54%. When comparing EOD waveforms of the new species with M. brevis, we found differences in repetition rate, the ratio between the first and second phase areas, and the polarity balance. The description of M. javieri n. sp. increases to five the number of species in the genus.
KEYWORDS: fish taxonomy; biodiversity; DNA barcode; electric organ discharge; neotropical region
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| Lateral view of Microsternarchus javieri n. sp. from the Negro River basin. A - Holotype (INPA-ICT 060886), 98.6 mm TL, 67.6 mm LEA; B - Paratype (ANSP 212283), 101.2 mm TL, 62.0 mm LEA; C -Non-type (INPA-ICT 28591), 86.9 mm TL, 60.4 mm LEA live specimen. |
Microsternarchus javieri, sp. nov. Cox Fernandes, Escamilla Pinilla, Alves-Gomes
Diagnosis: Microsternarchus javieri n. sp. is distinguished from its congeners in having a smaller maximum body depth [8 - 10% of LEA, vs. in M. bilineatus 9.8 - 12% of LEA; in M. brevis 8 - 11.2% of LEA (Figure 3a), M. longicaudatus 7.9 - 11.5% of LEA and M. schonmanni 8.2 - 11% of LEA]. M. javieri n. sp. is further distinguished from M. bilineatus by a combination of characters: slightly larger eye diameter (10 - 15% of HL, vs. 10.1 - 13.5% of HL, Figure 3b), longer caudal filament (26 - 44% of TL vs. 29.3 - 34.4% of TL), fewer caudal vertebrae 60 - 65 (N = 11) vs. 66 - 67 (N = 3), greater number of anal fin rays 146 - 174 vs. 138 - 161. M. javieri n. sp. is also distinguished from M. brevis by a much longer caudal filament (26 - 44% of TL vs. 12.8 - 20.9% of TL) and total length ...
Etymology: The specific epithet, javieri, is in honor of the late Javier Maldonado Ocampo [1977-2019], whose research on gymnotiforms, systematics, and conservation greatly contributed to our understanding of the Neotropical ichthyofauna. A masculine noun in apposition.
Carolina ESCAMILLA PINILLA, Cristina COX FERNANDES and José Antônio ALVES-GOMES. 2025. Microsternarchus javieri, A New Species of weakly electric fish (Gymnotiformes: Hypopomidae, Microsternarchini) from the Negro River Basin, Amazonas, Brazil. [Microsternarchus javieri, nova espécie de peixe elétrico (Gymnotiformes: Hypopomidae, Microsternarchini) da bacia do Rio Negro, Amazonas, Brasil] Acta Amaz. 55; DOI: doi.org/10.1590/1809-4392202401751
