Abstract
Critical swimming speeds of four trichomycterid fish species from epigean and hypogean environments were analyzed and compared: Trichomycterus itacarambiensis and Ituglanis passensis, both troglobitic from underground rivers; Trichomycterus brasiliensis, from epigean rivers; and Ituglanis sp., an undescribed troglophilic species from an underground stream. Swimming tests were conducted with a non-volitional apparatus in which fish swim against a progressive incremental water velocity until they longer resist the flow. Total length was significantly related to critical speed for only T. itacarambiensis. The critical speed obtained by each species, in decreasing order, with values in lengths per second (lengths/s), were: I. passensis (3.61), T. itacarambiensis (3.49), T. brasiliensis (3.11) and Ituglanis sp. (1.89). Swimming performance differed between the congeners T. itacarambiensis and T. brasiliensis, but did not differed between I. passensis and Ituglanis sp. The greater speed for the troglobitic species compared to that of the troglophilic and epigean species is probably related to seasonal flooding pulses that can be extremely severe in caves. Furthermore, during the tests, fish were observed using their mouth and/or barbels to fasten themselves to the substrate to avoid high flows.
Highlights
There are at least 11 troglobitic species of the family Trichomycteridae in Brazil, three of which belong to the genus Trichomycterus, including an undescribed species (Proudlove 2010; Bichuette and Rizzato 2012), and six to the genus Ituglanis (Proudlove, 2010; Rizzato and Bichuette 2014)
Twenty-four individuals (N=24) of the species Trichomycterus brasiliensis Lütken, 1874, which occurs in superficial streams, were caught with a trawl in the city of Luminárias (21°30'52"S, 44°52'29"W), in the state of Minas Gerais (MG)
We considered a valid test for critical speed to be when the specimen swam for at least 5 minutes, and for swimming behavior when the specimen attached for at least 25 minutes
Summary
Fish belonging to the order Siluriformes Cuvier, 1817, usually possess broad geographical distributions, with different species occurring in both freshwater, marine and brackish environments (Froese and Pauly 2019). Among the families of this order that occur in freshwater, Trichomycteridae Bleeker, 1858, stands out as one of the richest, with around 330 species (Fricke et al 2020) and 42 genera distributed throughout South America, Costa Rica and Panama (de Pinna 1998; Froese and Pauly 2019). Species from this family possess high plasticity in colonizing different environments and are diverse among Neotropical fish (Wosiacki and de Pinna 2008) with representatives in both surface and subterranean waters. Both Trichomycterus and Ituglanis contain species with subterranean populations, with many of them possessing troglomorphic traits (e.g. reduction of ocular structures and melanic pigmentation) (Fernández and Bichuette 2002), and are the two genera that best represent the family Trichomycteridae in hypogean environments (Trajano et al 2010)
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