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Life History of Gymnotus Refugio (Gymnotiformes; Gymnotidae): an Endangered Species of Weakly Electric Fish

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Life History of Gymnotus Refugio (Gymnotiformes; Gymnotidae): an Endangered Species of Weakly Electric Fish Environ Biol Fish (2017) 100:69–84 DOI 10.1007/s10641-016-0556-z Life history of Gymnotus refugio (Gymnotiformes; Gymnotidae): an endangered species of weakly electric fish Aline Salvador Vanin & Julia Giora & Clarice Bernhardt Fialho Received: 16 June 2016 /Accepted: 21 November 2016 /Published online: 28 November 2016 # Springer Science+Business Media Dordrecht 2016 Abstract The present study describes the life history of Keywords Electric-fish . Threatened species . Gymnotus refugio, a species classified as Endangered in Reproduction . Feeding the last published list of threatened species of the Brazilian fauna. The study was conducted at a conser- vation unity that protect one of the last remaining Introduction semideciduous forests in the region. The reproductive period was estimated as occurring from the end of The order Gymnotiformes is composed by freshwater winter to the last summer months. Gymnotus refugio weakly electric fishes, which are able to produce and exibited fractional spawning, the lowest relative fecun- detect electric fields with the function of localization and dity registered among the Gymnotifomes species stud- intra and interspecific communication (Crampton and ied at the present, and male parental care behavior. The Hopkins 2005). They can be found from southern analyses showed a seasonal pattern on the species diet, Mexico to Argentina, and in the Caribbean island of associating different food categories to winter, autumn, Trinidad (Albert and Crampton 2003). The genus and spring. According to food items analysis and esti- Gymnotus is the representative with the largest distribu- mated intestinal quotient, G. refugio was classified as tion among the order, including 40 valid species invertivorous, feeding mainly on autochthonous insects. (Eschmeyer and Fong 2016) occurring over their entire The results obtained herein suggest that the position of distribution area (Mago-Leccia 1994). Environmental G. refugio as an Endangered species might be influ- conditions (e.g., water flow, temperature, dissolved ox- enced by its territoriality, habitat specificity, parental ygen, conductivity and vegetation) are important factors care behavior, and low fecundity, reinforcing the impor- influencing the distribution of electric fishes (Crampton tance of swampy forest environment conservation as the 1998). These fishes also have several strategies which only means of the species maintenance. facilitate adaptations to environments with a large range of abiotic and biotic factors (Hopkins 1974;Kirschbaum 1975, 1979, 2000;Crampton1998;Albertand Electronic supplementary material The online version of this Crampton 2005), including air breathing adaptations to article (doi:10.1007/s10641-016-0556-z) contains supplementary material, which is available to authorized users. cope with prolonged periods of hypoxia or anoxia : : (Hopkins 1974; Crampton 1998; Kirschbaum 1975, A. S. Vanin J. Giora (*) C. B. Fialho 1979, 2000; Albert and Crampton 2005). Laboratório de Ictiologia, Departamento de Zoologia, Instituto de The recently described species, Gymnotus refugio Biociências, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves, 9500, Prédio 43435, Porto Alegre, RS CEP (Giora and Malabarba 2016), belongs to the species 91501-970, Brazil group Gymnotus pantherinus currently represented by e-mail: [email protected] 15 species. Gymnotus refugio was formerly 70 Environ Biol Fish (2017) 100:69–84 misidentified as either the species G. pantherinus effective ones requires knowledge on the species’ (Corrêa et al. 2015)orG. aff. pantherinus (Malabarba life history traits. Therefore, the present study aims et al. 2013) in the state of Rio Grande do Sul. Gymnotus to understand the particular biological predictors refugio is found inhabiting the interior of wetlands and related to the low distribution and abundance of edges of swampy forests composed by dense and float- G. refugio, which lead the species to the ing riparian vegetation (Ferrer et al. 2015), and is dis- Endangered category in southern Brazil. The re- tributed from the coastal rivers of the southern Rio sults concerning reproductive biology, gonadal Grande do Sul state to the southern Santa Catarina state maturation, and feeding habits unveiled subsidizing (Giora and Malabarba 2016). According to the last future conservation actions focusing the species published list of threatened fauna species of the Rio and its habitat. Grande do Sul state, G. refugio (quoted as Gymnotus pantherinus) is labelled as EN (Endangered) according to the UCN criteria (FZB 2014). This classification is Material and method based on the species distribution in the state, which covers an estimated area of only 24 km2,dueitshabitat Study area specificity, and restriction to streams and fragmented areas exposed to anthropic actions. Up until now, The sampling area is located in the Refugio da Vida G. refugio is easily found and noted in populations with Silvestre Banhado dos Pachecos (RVSBP) (30°09′57″S; higher number of specimens only in two conservation 50°84′99 W) in Viamão municipality, state of Rio areas: Refúgio da Vida Silvestre Banhado dos Pachecos Grande do Sul, Brazil. The RVSBP is a conservation (RVSBP) and Parque Estadual de Itapeva, being rare unit created in 2002, covering 2.560 ha inserted in the and scarce in all the other places where it has been Gravataí river basin, where the medium and low seg- registered (Giora and Malabarba 2016). ments are extremely impacted by human activities Characters related to measures of habitat condi- (IBGE 2010). According to Oliveira et al. (2005), the tions, behavior, and trophic requirements have fragments of swampy forest surrounding the Gravataí been useful for relating the distribution of fresh- river are the last remaining of semideciduous forest water fishes to environmental variables (Olden permanently submitted to the fluvial influence of the et al. 2006). On the other hand, life history traits river basin. The stream where G. refugio was sampled is are strong predictors of the vulnerability of fish characterized by murky water, abundant floating vege- populations as they determine how resilient a spe- tation, muddy substrate, and dense riparian vegetation cies is to disturbances such as habitat loss and the known as Mata Paludosa (= swampy forest). adverse effects of invasive species (Hamidan and Britton 2015). Reproduction represents one of the Sampling most important aspects of the biology of a species, the maintenance of viable populations depending The specimens of G. refugio were monthly sampled on its success (Suzuki and Agostinho 1997). from March/2011 to February/2012 between 9:00 and Feeding ecology is thoroughly linked to population 17:00 h. Fishes were collected using a dip net under dynamics and contributes to the understanding of floating vegetation and an electric fish finder (Crampton subjects such as resource partitioning, habitat pref- et al. 2007). In the field, the specimens sampled were erence, prey selection, predation, competition, tro- euthanized by immersion in 10% eugenol solution and phic ecology, and evolution (Braga et al. 2012). then fixed in 10% formalin solution. Water and air Since a disturbed ecosystem can affect directly the temperature, water pH, dissolved oxygen, and conduc- dynamic, seasonality, and behaviour of species, tivity were recorded at the time and place of sampling. developing conservation efforts can require com- The monthly amounts of rainfall (in millimeters) and prehension of patterns that shape the biological time of sunshine (in hours) were obtained at the 8th cycles and the ecological interaction between these District of Meteorology of Porto Alegre (available at organisms and their habitat. On account of the Meteorological databank for Education and Research of conservation status of G. refugio populations, con- the National Institute of Meteorology, Brazil, station servation measures are needed and the design of 83967). Environ Biol Fish (2017) 100:69–84 71 Data analysis randomly removed from each selected gonad and the largest possible oocyte diameter was obtained by exam- In the laboratory, fishes were transferred to 70% ethanol ination under a stereomicroscope equipped with a solution and, afterward, the total length in millimeter millimetered ocular (Vazzoler 1996). and total weight in grams were measured. Individuals The sex ratio was determined by the distribution of were dissected to register gonad and stomach weight, male and female frequency during the sample period. and intestine length. Stomach repletion index (RI) and The χ2 test (α <0.05) was applied to determine the gonadosomatic index (GSI) were estimated following existence of significant differences between the propor- the formula adapted from Santos (1978). These indexes tion of males and females in the population. The same represent the percentage organ weight related to fish test was also applied to the distribution of relative fre- total weight: RI = Ws ×100/Wt and GSI = Wg ×100/Wt. quencies of males and females in different total length Ws corresponds to stomach weight, Wg to gonad classes in order to test sexual dimorphism related to total weight, and Wt to total weight. The intestinal quotient length. (IQ) represents the ratio of the intestine length related to Stomach content analysis was performed with the the fish total length: IQ = Li/Lt. Li corresponds to the help of a stereomicroscope and the items of stomach intestine length and Lt to the total length. contents were identified to
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