Dermal lip protuberances associated with aquatic surface respiration in juveniles of the piscivorous characid Salminus brasiliensis (Actinopterygii: Characidae)

Abstract

Some South American freshwater fishes can improve their capability of aquatic surface respiration (ASR) by developing dermal lip protuberances in the lower jaw. This adaptation was thought to be limited to omnivorous or herbivorous fishes. The present work provides the first evidence that juveniles of a piscivorous characid, Salminus brasiliensis, develop dermal lip protuberances during periods of hypoxia in floodplain ponds of the Salado River, in Argentina. The protuberance of S. brasiliensis involves dermal portions of both jaws exhibiting lateral lobes on the sides of the mouth arranged in the vertical plane. Water dissolved oxygen concentrations less than or equal to 1.05 mgl -1 were associated with a remarkable increase in lip protuberance. The lateral lobes of the protuberance in this species may limit the access of water to the anterior portion of the mouth which is positioned nearer to the oxygenated surface water during ASR. Finally, ASR, complemented with the development of dermal lip protuberances, can be considered a valuable strategy to survive in hypoxic environments, even for carnivorous fishes with elevated oxygen requirements.Alguns peixes de água doce da América do Sul podem melhorar o desempenho da respiração aquática superficial (RAS) desenvolvendo protuberâncias dérmicas labiais na mandíbula. Considerava-se que essa adaptação era limitada aos peixes onívoros ou herbívoros. Este trabalho apresenta os primeiros indícios de que juvenis de um caracídeo piscívoro, Salminus brasiliensis, desenvolvem protuberâncias dérmicas labiais durante períodos de hipoxia em lagoas de várzea do rio Salado, Argentina. As protuberâncias de S. brasiliensis envolvem porções dérmicas das duas mandíbulas e exibem lóbulos laterais ao lado da boca dispostas no plano vertical. Concentrações de oxigênio dissolvido na água, inferiores ou iguais a 1,05 mgl -1 , foram associadas a um aumento notável no desenvolvimento das protuberâncias labiais. Nesta espécie os lóbulos laterais da protuberância podem limitar o acesso de água à porção anterior da boca, que está posicionada mais perto da superfície da água oxigenada durante a RAS. Finalmente, a RAS, complementada com o desenvolvimento de protuberâncias dérmicas labiais, pode ser considerada uma valiosa estratégia para a sobrevivência em ambientes hipóxicos, mesmo para peixes carnívoros com elevada demanda de oxigênio.

Phenotypic plasticity associated to environmental hypoxia in the neotropical serrasalmid Piaractus mesopotamicus (Holmberg, 1887) (Characiformes: Serrasalmidae)

“…Previous field studies on lip protuberances observed high variation in morphological response to hypoxia (Braum & Junk, 1982;Winemiller, 1989;Scarabotti et al, 2009). This variability was attributed to intrapopulation variability, spatial heterogeneity in DO and to small errors in DO measurements near the critical concentration.…”

“…ASR is a widespread mechanism in fishes to exploit the oxygen available in the thin layer of surface water, where rapid diffusion maintains high oxygen concentrations even during hypoxia (Lewis, 1970;Kramer & Mehegan, 1981). Many South American characiform species optimize the performance of ASR developing reversible dermal protuberances in the jaws that improve the influx of surface water into the mouth (Winemiller, 1989;AlmeidaVal et al, 2006;Florindo et al, 2006;Scarabotti et al, 2009Scarabotti et al, , 2011. Protuberances are edematous structures (Saint-Paul & Bernardinho, 1988;Saint-Paul & Soares, 1988;Scarabotti et al, 2011), which develops in 2 to 4 hours and revert completely when oxygen conditions are reestablished (Branson & Hake, 1972;Braum & Junk, 1982;Saint-Paul & Bernardinho, 1988).…”

Morphological plasticity associated with environmental hypoxia in characiform fishes from neotropical floodplain lakes

“…One individual of Hyphessobrycon luetkenii (Characidae), collected at a DO level of 1.20 mg·l −1 , showed an intermediate lip development in comparison with voucher specimens, but this single example is insufficient to confirm lip protuberance occurrence in this species. Data referring to Salminus brasiliensis were presented in a previous work (Scarabotti et al 2009). The eleven remaining species belonging to the genera Astyanax, Aphyocharax, Ctenobrycon, Mylossoma, Brycon, Triportheus, Oligosarcus and Acestrorhynchus (Table 1), were observed with fully developed lip protuberances.…”

“…5 Coefficients of variation indicating the plasticity of each morphometric variable of lip development in ten species of characiform fishes. A abr = Astyanax abramis, A asu = Astyanax asuncionensis, A fas = Astyanax fasciatus, A cor = Astyanax correntinus, C all = Ctenobrycon alleni, A ani = Aphyocharax anisitsi, B orb = Brycon orbignyanus, M dur = Mylossma duriventre, T par = Triportheus paranensis, A pan = Acestrorhynchus pantaneiro 1982; Saint-Paul and Bernardinho 1988;Saint-Paul and Soares 1988;Winemiller 1989;Schmitter-Soto et al 2008;Scarabotti et al 2009). Although the phylogenetic relationships between characiform families and subfamilies have not been completely elucidated (Ortí and Meyer 1997;Malabarba et al 1998;Calcagnotto et al 2005), the development of dermal lip protuberances have been reported in evolutionary distant taxa of characiforms.…”

“…Although dermal lip protuberances have been described in many species, they appeared to be restricted to surfacefeeding herbivorous and omnivorous characids (Winemiller 1989). Nevertheless, we have recently observed dermal extensions in a largely piscivorous characid (Scarabotti et al 2009). In addition, in all above cited studies, dermal lip protuberances were reported to be limited to the anterior border of lower jaw, although comparative measurements on the upper jaw have not been addressed.…”