Ecology of Mylesinus paucisquamatus Jégu & Santos, 1988, an endangered fish species from the rio Tocantins basin

Abstract

Mylesinus paucisquamatus is a threatened fish endemic to the rio Tocantins basin, with little information about its natural history. Using monitoring data obtained between 1998 and 2009, we investigated the spatial distribution, feeding and reproduction of this species in a long stretch of the middle-upper rio Tocantins. Eighty-one individuals were captured over a decade of intensive sampling. In addition, we recorded the species in only 13 out of 35 sites, particularly in the Tocantins and Paranã rivers. Most individuals were captured alone, while the remaining formed small groups. These results indicate that this fish is rheophilic and rare. We recorded seasonal variation in fish abundance, with higher values during the dry season, indicating seasonal movements. The species is herbivorous and specialized in the consumption of plants attached to substrates, particularly bryophytes. We also observed seasonality in reproduction, since reproductive activity increased during the early dry season. These ecological traits, e.g., rarity, rheophilic and specialized feeding habits, indicates that M. paucisquamatus is vulnerable to environmental changes, particularly river damming. Considering that three large dams currently regulate and fragment this section of the rio Tocantins, the persistence of this species is jeopardized, demanding effective conservation actions.Mylesinus paucisquamatus é um peixe endêmico da bacia do rio Tocantins, ameaçado de extinção mas com escassa informação sobre sua história natural. Usando dados de monitamentos obtidos entre 1998 e 2009, investigamos a distribuição espacial, ecologia alimentar e reprodução desta espécie em um longo trecho do médio-alto rio Tocantins. Um total de 81 indivíduos foi capturado em mais de uma década de monitoramento. Além disso, a espécie ocorreu em apenas 13 dos 35 locais monitorados, principalmente nos canais dos rios Tocantins e Paranã. A maior parte dos indivíduos foi capturado sozinho, enquanto que os demais foram capturados em pequenos grupos (dois a cinco indivíduos). Tais resultados indicam que a espécie é reofílica e rara. Registramos variação sazonal de abundância, com valores mais elevados durante a estiagem, o que indica deslocamentos sazonais. A espécie é herbívora e especializada no consumo de plantas ancoradas em substratos, particularmente briófitas. A reprodução foi também sazonal, com aumento da atividade durante o início da estação de estiagem. Essas características ecológicas, e.g., raridade, hábito reofílico e hábito alimentar especializado, indica que M. paucisquamatus é vulnerável a mudanças ambientais, particularmente o barramento de rios. Considerando que atualmente três grandes barragens regulam e fragmentam esse trecho do rio Tocantins, a persistência da espécie encontra-se severamente ameaçada, demandando ações de conservação efetivas.

Remarkable Geographic Structuring of Rheophilic Fishes of the Lower Araguaia River

“…One of these specializations is the use of podostemaceous plants as a place of shelter, growth, foraging and direct consumption by herbivorous species (Flausino Junior et al, 2016 ). As an example, strongly rheophilic pacus species (Characiformes: Serrasalmidae), such as those of the genera Mylesinus and Tometes , present cutting teeth used in leaf pruning of these plants (e.g., Jégu and Santos, 1988 ; Santos et al, 1997 ; Vitorino Júnior et al, 2016 ; Andrade et al, 2017 ). The strong dependence on podostemaceous mats as food makes these pacus particularly vulnerable to the environmental impacts resulting from dam construction.…”

One thousand DNA barcodes of piranhas and pacus reveal geographic structure and unrecognised diversity in the Amazon

“…While some species such as the tambaqui ( Colossoma macropomum ) and the piranhas Serrasalmus rhombeus and Catoprion mento are widely distributed and found in most major river systems 4 , others have highly restricted distributions. Ossubtus xinguense , for example, is endemic to the rapids of the middle Xingu River 5 , while Mylesinus paucisquamatus is endemic to the rapids of the Tocantins River 4 , 6 , 7 . Other rheophilic species of the genera Tometes and Utiaritichthys are also endemic to the rapids of other rivers 8 – 10 .…”