Trophic strategy of Atlantirivulus riograndensis (Cyprinodontiformes: Rivulidae), a non-annual rivulid threatened by extinction, in a perennial environment, Brazil)

Abstract

Rivulidae includes non-annual fish of perennial habitats and annual fish of temporary wetlands. The objective of this research was to investigate the trophic strategy of Atlantirivulus riograndensis in a perennial environment. Sampling occurred in an environmental conservation unit in the Pampa biome, Brazil. Quantification of the diet followed the volumetric method. Consumption of autochthonous material as the main food source of the species followed the pattern of Rivulidae. Species is zooplanktonic when young. Food spectrum is broadened and insectivorousness increases with ontogeny, revealing a specialist trend in the feeding strategy of A. riograndensis. The most diverse feeding occurs in the spring and summer seasons in which the presence of larger fish was more frequent than in other seasons. The increased consumption of microcrustaceans in the fall was related to smaller individuals, captured in greater quantities in this post-reproductive period. The lowest diversity of dietary items occurs during the winter and may reflect the lower diversity of food resources available in this season or the transition from juvenile to adult diet, with consumption of autochthonous Diptera by medium sized fish.Rivulidae inclui peixes não anuais de habitats perenes e peixes anuais de alagados temporários. O objetivo desta pesquisa foi investigar a estratégia trófica de Atlantirivulus riograndensis em um ambiente perene. A amostragem ocorreu em uma unidade de conservação ambiental no bioma Pampa, Brasil. A quantificação da dieta seguiu o método volumétrico. O consumo de material autóctone como principal recurso alimentar da espécie seguiu o padrão da família Rivulidae. A espécie é zooplanctívora quando juvenil. O espectro alimentar é ampliado e a tendência à insetivoria aumenta com a ontogenia, revelando traços especialistas na estratégia alimentar de A. riograndensis. A alimentação mais diversificada ocorreu na primavera e no verão, estações em que a presença dos peixes maiores foi frequente que em outras estações. O aumento no consumo de microcrustáceos no inverno foi relacionado aos indivíduos menores, capturados em maior quantidade neste período pós-reprodutivo. A menor diversidade de itens alimentares ocorreu durante o inverno e pode refletir uma menor diversidade de recursos alimentares disponíveis nesta época do ano ou a transição da dieta de juvenil para adulto, com consumo de Diptera autóctone por peixes de tamanho médio.

Ontogenetic variations and feeding habits of a Neotropical annual fish from southern Brazil

“…This annual fish shows a wide feeding spectrum (25 food items), consuming mostly small crustaceans (mainly Cladocera and Copepoda), and autochthonous insects (mainly larvae of Diptera). A generalist diet, consisting of small autochthonous invertebrates, was also found by Keppeler et al (2013) to C. fulgens (52 food items) and by Gonçalves et al (2011) and Laufer et al (2009) to C. melanotaenia (26 and 23 food items, respectively), suggesting that this characteristic can be standard in the family (Harrington & Rivas, 1958;Huehner et al, 1985;Costa, 1987Costa, , 1998Costa, , 2009Davis et al, 1990;Taylor, 1992;Shibatta & Rocha, 2001;Shibatta & Bennemann, 2003;Arim et al, 2010;Abilhoa et al, 2010a, b;Contente & Stefanoni, 2010;Polačik & Reichard, 2010;Cavalheiro & Fialho, 2016;Loureiro & de Sá, 2016;Ortiz & Arim, 2016). The generalist feeding strategy is an expected characteristic for the life history of C. fulgens and other annual fishes, since they live in temporary habitats with varied environmental conditions, conferring high resistance to changes in food resources (Costa, 1995(Costa, , 2002aLaufer et al, 2009;Polačik & Reichard, 2010;Keppeler et al, 2013).…”

“…Ontogenetic feeding changes are well known in fishes (Wootton, 1999;Amundsen et al, 2003) and have been recorded in some Cynolebiidae species (Santos-Filho, 1997;Laufer et al, 2009;Abilhoa et al, 2010b;Canavero et al, 2013;Keppeler et al, 2013Keppeler et al, , 2015Cavalheiro & Fialho, 2016;Ortiz & Arim, 2016). These ontogenetic changes in annual fish populations may reduce a potential intraspecific competition for prey items through diet segregation or by reducing direct interactions through spatial and/or temporal segregation (Laufer et al, 2009;Canavero et al, 2013;Ortiz & Arim, 2016), since is known that competitive interactions are stronger among individuals of similar body sizes (Santos-Filho, 1997;Canavero et al, 2013;Ortiz & Arim, 2016).…”

“…Also, this may be occuring due to a spatial overlap between males and females, resulting in a similar prey capture situation and ability (Contente & Stefanoni, 2010). On the other hand, Laufer et al (2009) for two Austrolebias species, Keppeler et al (2013) for C. fulgens, and Cavalheiro & Fialho (2016) for A. riograndensis, found differences in prey selectivity among males, females and juveniles, attributed to morphological characteristics that could predispose intersexual dissimilarities in diet.…”

“…Juvenile fish should maximize growth and survival due to their vulnerability in the early stages of life (Pilatti & Vanni, 2007), consuming abundant prey itens with important sources of protein and keratin, such as crustaceans (CantoMaza & Vega-Cendejas, 2007). Various studies have demonstrated the preference of juvenile cynolebiids for crustaceans Keppeler et al, 2013;Cavalheiro & Fialho, 2016), probably due to the high availability of this resource, the small size of this prey and the limited agility of juvenile fish. Finally, adults of C. fulgens had a tendency to ingest, in addition to crustaceans, a greater amount of autochtonous insects, such as Diptera and Odonata larvae.…”

Ontogeny of feeding by Astyanax paris in streams of the Uruguay River Basin, Brazil

“…The differential use of food resources is a wellknown intraspecific strategy to avoid trophic niche overlap between juveniles and adults in several freshwater fish species (Bonato and Fialho, 2014;Cavalheiro and Fialho, 2016;Dala-Corte et al, 2016). Some species may therefore concentrate on different food resources at different stages of their development (Rudolf and Lafferty, 2011).…”