Opportunistic predation of fish by anomuran crabs (Crustacea, Anomura, Aeglidae) in rivers of southern Brazil

Predação oportunista de peixes por eglídeos (Crustacea, Anomura, Aeglidae) em rios do Sul do Brasil

SHORT COMMUNICATIONS

Opportunistic predation of fish by anomuran crabs (Crustacea, Anomura, Aeglidae) in rivers of southern Brazil

Predação oportunista de peixes por eglídeos (Crustacea, Anomura, Aeglidae) em rios do Sul do Brasil

Marcoandre Savaris¹; Silvana Lampert; André Trevisan; Setuko Masunari

Departamento de Zoologia, Centro Politécnico, Universidade Federal do Paraná – UFPR, Jardim das Américas, CP 19020, CEP 81531-980, Curitiba, PR, Brasil

ABSTRACT

The opportunistic predation on the fishes Astyanax fasciatus and Crenicichla sp. entangled in gill net by the aeglid crabs Aegla grisella and Aegla singularis was observed in rivers of southern Brazil. These events occurred in two rivers located at the National Forest of Passo Fundo, in Mato Castelhano municipality, Rio Grande do Sul State and Tangará municipality, Santa Catarina State. In both places the fish showed similar wound pattern, with eyes and fins being consumed first. However, predation of the whole body was also recorded, probably due to the high number of aeglid crabs feeding on the same individual. This record intended to contribute for understanding the natural diet of these crabs in freshwater environments.

Keywords: diet, fish, behavior, aeglid crabs.

RESUMO

A predação oportunista dos peixes Astyanax fasciatus e Crenicichla sp. emalhados em rede de espera pelos eglídeos Aegla grisella e Aegla singularis foi observada em rios do Sul do Brasil. Estes eventos ocorreram em dois rios na Floresta Nacional de Passo Fundo, município de Mato Castelhano, RS e no município de Tanguará, SC. Em ambos os locais os peixes apresentavam um padrão de mutilação semelhante, com olhos e nadadeiras sendo consumidos primeiramente. No entanto, a predação de todo o corpo também foi registrada, provavelmente em decorrência do elevado número de eglídeos se alimentando de um mesmo indivíduo. Esse registro visa contribuir para o entendimento da dieta natural dos eglídeos em ambientes de águas continentais.

Palavras-chave: dieta, peixes, comportamento, eglídeos.

Introduction

The family Aeglidae Dana, 1852 is the only anomuran crustacean that lives in continental waters. Its species are found in clear and well oxygenated waters of streams, rivers, lakes and stream caves; usually they are hidden under rocks and plant debris (Bond-Buckup & Buckup 1994, Bond-Buckup 2003, Bond-Buckup et al. 2008, Dalosto & Santos 2011).

According to the criteria of the International Union for Conservation of Nature (IUCN), from a total of 70 know species 23 are threatened, mainly due to their endemic distribution and to the visible degradation of freshwater environments. Therefore, these organisms should be a priority for ecological studies aiming the establishment of conservation measures (Bueno & Bond-Buckup 2004).

The feeding habit has been investigated in the following aeglids: Aegla laevis laevis Latreille, 1818, Aegla perobae Hebling & Rodrigues, 1977, Aegla platensis Schmitt, 1942, Aegla leptodactyla Buckup & Rossi, 1977, Aegla camargoi Buckup & Rossi, 1977, Aegla lingulata Bond-Buckup & Buckup, 1994 and Aegla longirostri Bond-Buckup & Buckup, 1994. They were characterized as opportunistic omnivorous, feeding on diversified food items such periphyton, organic matter coming from allochthonous plants, aquatic invertebrates, fish scales and fine particulate organic matter (Bahamonde & López 1961, Burns 1972, Arenas 1978, Isler 1988, Magni & Py-Daniel 1989, Lara & Moreno 1995, Medina 1998, Bueno & Bond-Buckup 2004, Castro-Souza & Bond-Buckup 2004, Santos et al. 2008).

Studies based on stomach contents analysis, using more refined statistical methods have been only published recently. Castro-Souza & Bond-Buckup (2004) evaluated the natural diet of A. camargoi and A. leptodactyla that occur in sympatry at Divisa River, in São José dos Ausentes municipality, Rio Grande do Sul State and Bueno & Bond-Buckup (2004) characterized the diet of A. plantensis and A. lingulata, from Arroio do Mineiro, southern Brazil. These four species have been considered opportunistic omnivorous, confirming the results of previous authors.

More recently, Santos et al. (2008) recorded plant tissues, organic material in advanced state of digestion, fragments of adults insects, aeglid body parts, clam shells, fish scales, and dipteran larvae in the stomach content of A. longirostri, from central region of Rio Grande do Sul State. On the other hand, aeglids constitute an important food item in the diet of the trouts Oncorhynchus mykiss (Walbaum, 1792) and Salmo trutta fario Linnaeus, 1758 (Burns 1972, Arenas 1978, Isler 1988, Lara & Moreno 1995) and of the otter Lontra provocax (Thomas, 1908) (Medina 1998).

The present note is a record of an opportunistic predation on dead or dying fishes that were entangled in nets by two aeglid species in southern Brazil. The events occurred at a stream within the National Forest of Passo Fundo, in Mato Castelhano municipal