Underwater: A Journey into the Unknown World of Small-sized Neotropical Fishes

Latest update August 31, 2019 Started on January 1, 2012
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Check out an ichthyology team's effort on understanding the evolution of neotropical small-sized fishes and their distribution through geological time. Instagram: @underwater.blog

January 1, 2012
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In The Field

Today is our third day of fieldwork in the Amazon. During this period, I, Filipe and Pedro explored some specific habitats, such as litter leaf, sandbanks, and roots of aquatic plants. Among the stunning diversity of fishes collected in only 72 hours of expedition, the catfish species Helogenes marmoratus deserves some attention.
Fishes of the genus Helogenes were previously allocated in their own family, Helogenidae. From de Pinna & Vari’s (1995) paper on, these catfishes are considered a distinct lineage (subfamily Helogeninae) of the family Cetopsidae (commonly known as “candiru-açu” or “whale candiru/candiru baleia”). Helogenes currently comprises four species distributed throughout the Amazon, Orinoco and Tocantins River basin and in coastal rivers of the Guianas. Species of Helogenes are easily recognized by a very long anal fin, the lack of spines in both dorsal and pectoral fins, the ventral lobe of the caudal fin wider than the dorsal lobe and an adipose fin minute or absent. Individuals of H. marmoratus are found in clear or black waters in Brazil, Peru, Ecuador, Venezuela, Suriname, Guiana and French Guiana. They are brownish/reddish resembling dead leaves and inhabit litter, plant debris and roots of aquatic plants. The coloration pattern usually acts as a camouflage: these catfishes can be mistaken as a piece of wood when laying on their side to rest. Helogenes marmoratus is also known for jumping outside the water during rotenone fishing by Tukano and Tukuya indigenous people and then jumping back on the water after the water is clear. This species distinguishes from the other species of the genus by differences in fin rays counts.

References: de Pinna, M.C.C. & Vari, R.P. (1995). Monophyly and Phylogenetic Diagnosis of the Family Cetopsidae, with Synonymization of the Helogenidae (Teleostei: Siluriformes) Sazima, I., Carvalho, L. N., Mendonça, F. P., & Zuanon, J. (2006). Fallen leaves on the water-bed: diurnal camouflage of three night active fish species in an Amazonian streamlet. Neotropical Ichthyology, 4(1), 119–122.