A remarkable sand-dwelling fish assemblage from central Amazonia, with comments on the evolution of psammophily in South American freshwater fishes

Abstract

We studied a specialised assemblage of sand-dwelling fish species from a streamlet in central Amazonia. The five sanddwelling species comprised 15.2 % of the total number in the streamlet (33 species). Two of the sand-dwellers are daytime foragers, Characidium cf. pteroides (Crenuchidae) and Stauroglanis gouldingi (Trichomycteridae), whereas three ones are night-time foragers, Gymnorhamphichthys rondoni (Rhamphichthyidae), "Imparfinis" pristos and Mastiglanis asopos (Heptapteridae). With the exception of C. cf. pteroides, the remainder species bury in the sand during their resting period. All five species bear a cryptic, sand-colour pattern, and some are translucent, traits which we regard as advantageous both for evasion from predators and for approaching prey (for the daytime foragers). All five species are microphagous carnivores and their foraging tactics range from generalised sit-and-wait (C. cf. pteroides) to active searching for interstitial prey (G. rondoni). A unique "drift-trap" system made up by the extended barbels and filamentous first pectoral-fin rays is employed by M. asopos. We regard the small size and low number of vertebrae (which is functionally expressed by fast displacements in the sand) as additional features advantageous to explore the sand habitat, allowing diving quickly in the substrate to evade predators and to forage for small prey in sand interstices or plant debris. The relationship between morphological and behavioural characters suited to life in sandy substrates is examined under the perspective of the current phylogenies for each group of psammophilous fishes here studied. The mapping of these characters demonstrates that not all of them evolved specifically for strict psammophily. Instead, some of them may represent the final step of a transformation series or synapomorphies of higher hierarchical levels. Several characters linked to psammophily, such as small body, large eyes, and scarce pigmentation are probably paedomorphic traits. We consider that the little variable specific composition of fish sand-dwelling assemblages and the wide (although patchy) geographical distribution of their species in the Amazon are due to the widespread occurrence and low complexity of this specialised habitat. The pre-existence of benthic habits, small size, and the broad distribution of rivers with sandy beds, mainly in the Amazon and Orinoco basins, possibly played a determinant role in the origin and diversification of psammophilous assemblages among freshwater fishes in South America.Estudamos uma comunidade especializada de espécies de peixes psamófilos de um igarapé na Amazônia central. As cinco espécies psamófilas correspondem a 15.2 % do número total estimado de espécies do igarapé (33 espécies). Duas das espécies psamófilas são forrageadores diurnos, Characidium cf. pteroides (Crenuchidae) e Stauroglanis gouldingi (Trichomycteridae), ao passo que três são forrageadores noturnos, Gymnorhamphichthys rondoni (Rhamphichthyidae), "Imparfinis" pristos e Mastiglanis asopos (Heptapteridae)...

Following food clouds: feeding association between a minute loricariid and a characidiin species in an Atlantic Forest stream, Southeastern Brazil

“…Sazima, 1986;Sabino & Castro, 1990;Aranha et al, 1998;Sabino & Silva, 2004, Zuanon et al, 2006 revealed the use of two main foraging tactics: "sit-and-wait predation" (sensu Sazima, 1986), in which the fish stays stationary on the bottom and preys on small invertebrates spotted in the bottom or drifted by the current; and "hunting by speculation" (sensu Curio, 1976), in which the fish actively search for preys buried in the upper layer of the substrate. In this sense, we suggest that the following behavior displayed by Characidium sp.…”

Resource use by two electric fishes (Gymnotiformes) of the National Forest Saracá-Taquera, Oriximiná, Pará

“…Gymnorhamphichthys rondoni inhabits sandy bottoms with high or low flow due to its psammophilous behavior (Zuanon et al, 2006), which explain both its occurrence on sandy bottoms and on riffles, where individuals bury in the sand during the daytime. On the other hand, G. coropinae is associated with heterogeneous microhabitats with marginal vegetation, crevices or litter bottom.…”

“…According to Zuanon et al (2006), G. rondoni is dependent on prey that inhabits sandy bottom and feeds predominantly on Dipteran and Coleopteran larvae that are buried in the sand. A similar pattern was found by Tesk et al (2014) for the congeneric species G. petiti in Amazonian streams, which feeds predominantly on aquatic immature insects and nematodes -although the latter might have been mistaken parasitic nematodes for dietary items.…”

“…riffles, sand bottom areas) and food resources by two species of electric fish from two different Gymnotiformes families, Gymnorhamphichthys rondoni (Miranda Ribeiro, 1920) (Rhamphichthyidae) and Gymnotus coropinae Hoedeman, 1962 (Gymnotidae), in the Saracá-Taquera National Forest, Oriximiná, Pará. Fish of these genera feed predominantly on autochthonous invertebrates and display different foraging behaviors (Zuanon et al, 2006;Ferriz, Iwaszkiw, 2014), but no further information about their trophic ecology in the Amazon is available due to the difficulty in sampling specimens profusely and with temporal consistency.…”

“…space and food) by these two gymnotiforms in Amazonian headwater streams, we analyzed: (i) the proportion of microhabitat types used; (ii) diet composition; (iii) trophic niche breadth and overlap; and (iv) populational and individual strategies for the consumption of food resources. We expect that the use of different microhabitats distinguishes both species due to the known psammophilous behavior of G. rondoni (Zuanon et al, 2006), while G. coropinae does not exhibit known morphological specializations to occupy sandy bottom microhabitats. Furthermore, the diet of the species are expected to differ because the use of different microhabitats would supposedly provide different potential prey and also because the morphological specialization (elongated snout) exhibited by G. rondoni suggests a more restricted, specialized diet.…”