The origin of melanism has been often associated with cryptic habits, driven by selection for camouflage, sometimes independently arising in closely related species. Field studies in Atlantic Forest rivers of south-eastern Brazil have indicated the occurrence of three melanic species in the catfish genus Trichomycterus: Trichomycterus immaculatus, Trichomycterus nigricans, and T. quintus Costa sp. nov. We performed a molecular analysis using two nuclear and two mitochondrial genes (2811 bp) for 62 trichomycterines and eight outgroups, in which monophyly of a group here named as the T. nigricans-nigroauratus clade is highly supported. It comprises two subclades, the T. nigricans group (containing Trichomycterus caipora, T. immaculatus, T. nigricans, and Trichomycterus santaeritae) and the Trichomycterus nigroauratus group (containing Trichomycterus maculosus, T. nigroauratus, and T. quintus). Ancestral state reconstructions indicate that melanism has arisen independently in each species exhibiting overall black colouration, which may be favoured by the strict nocturnal habits of these three species. However, whereas in the T. nigricans group cryptic habits precede the origin of melanism, in the T. nigroauratus group these events occur simultaneously during the evolution of T. quintus. Two melanic species, T. immaculatus and T. quintus, are sympatric but inhabit different habitats, suggesting some ecological divergence. Oppositely to the crypsis evolutionary trend, the analysis indicates a reversal to diurnal habits in the psammophilic T. santaeritae. This species, uniquely among congeners of the T. nigricans-nigroauratus clade, has a colour pattern consisting of dark brown blotches on a pale yellow colour ground and relatively large eyes, allowing sandy habitat camouflage and visual orientation during foraging activity, respectively, interpreted as adaptive morphological changes parallelly found in other diurnal psammophilic trichomycterids.

黑色素的起源通常与隐性习性有关，这是由迷彩的选择驱动的，有时在密切相关的物种中独立出现。在巴西东南部的大西洋森林河流领域的研究已经表明在鲶鱼属3种黑色素发生Trichomycterus：Trichomycterus immaculatus，Trichomycterus皮病和T.昆图斯科斯塔SP。十一月 我们使用两个核和两个线粒体基因（2811 bp）对62个毛癣菌和8个外群进行了分子分析，其中高度支持了这里称为T. nigricans-nigroauratus进化枝的单性。它包括两个小村庄，即T. nigricans基（含有Trichomycterus caipora，T. immaculatus，T.皮症，和Trichomycterus santaeritae）和Trichomycterus nigroauratus组（含有Trichomycterus maculosus，T. nigroauratus，和T.昆图斯）。祖先状态的重建表明，黑色素已经在每个呈现出整体黑色的物种中独立出现，这可能是由于这三个物种严格的夜间习惯所致。但是，在黑T. nigricans群中，隐性习性先于黑化病的起源，而在T. nigroauratus中这些事件在藜的进化过程中同时发生。两种黑色的物种，即T. immaculatus和T. quintus是同胞的，但栖息于不同的栖息地，这表明存在一定的生态差异。与低温昆虫的进化趋势相反，该分析表明嗜嗜性桑氏梭菌的昼夜习性逆转。该物种，在黑T. nigricans-nigroauratus的同类中独特 进化枝具有由浅黄色斑点上的深褐色斑点和相对较大的眼睛组成的颜色模式，在觅食活动期间分别允许沙质栖息地伪装和视觉取向，这被解释为在其他昼夜嗜粉毛癣菌中同时发现的适应性形态变化。