一線鉛筆燈 (Nannostomus unifasciatus "Rio orinoco")

一線鉛筆燈 (Nannostomus unifasciatus), 俗名 One-lined Pencilfish, 因身體上長有一條黑寬帶而命名, 外型及日常動態, 與其共生在同一流域的騎士鉛筆燈 (Nannostomus eques) 非常相似, 特徵是尾鰭下葉長有一紅印, 黑帶生長位置由吻部伸展至尾鰭, 而且會隨狀態表現及外界影響, 表現時深時淺, 並喜愛集結於有掩護物如枯木或水草叢的地方活動, 泳姿有如在水中飄浮的梗枝, 藉此被過獵食者的攻擊, 個性非常溫和;

一線鉛筆燈的產地分佈廣泛, 據悉該種有兩個不同產地, 尾斑表現有差異的地域種存在, 而以下是節錄自seriouslyfish 對該種的產地報告:-

Type locality is given as ‘near mouth of Rio Negro, Brazil’, but this species is currently accepted to range throughout much of the upper Amazon basin in Brazil, Bolivia, and probably Colombia, plus the upper Orinoco system in Colombia and Venezuela, Essequibo and Demerera rivers in Guyana.
An introduced population exists in Trinidad and Tobago.
Records exist from various tributary drainages including the rios Negro, Jutaí,  in the Amazon, and the Casiquiare, Guaviare, Inírida, and Vita in the Orinoco basin.

Seriouslyfish 對該種的報告原文