Feeding dynamics and ecomorphology of Oligosarcus jenynsii (Gunther, 1864) and Oligosarcus robustus (Menezes, 1969) in the Lagoa Fortaleza, southern Brazil

Abstract

Oligosarcus jenynsii and Oligosarcus robustus are fishes of Characidae family that occur in Rio Grande do Sul, Uruguay and northern Argentina. This work purported to study the feeding dynamics (repletion and hepatosomatic indexes and condition factor) over time, and to investigate the coexistence of these two species by evaluating the partition of resources using qualitative and quantitative analyses of diet, temporal and spatial segregation throughout the water column and some ecomorphological aspects of the species in the Lagoa Fortaleza. Specimens were sampled monthly, from May 2000 to April 2001 during 24 h/month, using stationary gill nets of different mesh sizes. The records of each individual included total and standard length; total, stomach and liver weight; sex and stomach repletion. The variation of the mean values of repletion index and relative frequencies of stomach repletion stages indicate that O. jenynsii and O. robustus do not present seasonal differences in feeding intensity. The hepatosomatic index shows an allocation of energy to the liver during every period except reproduction, when part of the energy is used for gonad maturation. The estimated condition factor for both species reveals an increase in the reproductive period, evidencing the influence of gonads upon the condition of the fish. The diet analysis revealed that O. robustus is piscivorous, whereas O. jenynsii is a generalist carnivore, tending to piscivory as well. The active period of O. robustus is more concentrated at sunrise and sunset, whereas O. jenynsii is continually active, a characteristic related to hunting for prey. The ecomorphological analysis revealed differences between the two species in the dimensions of the mouth. Evidence suggests that the species coexist, sharing food sources, differing in oral morphology but ingesting similar prey, possibly because food is not a limiting factor in the environment.

Population structure, condition and diet of Oligosarcus paranensis (Menezes & Gery, 1983) (Osteichthyes: Characidae) at two reservoirs in South Brazil

“…The classic sex ratio in fish is 1:1 (Wootton 1999), however, it can vary considerably among species and populations of the same species in different environments (Nikolsky 1978), as it was observed in the population of Fiú (prevalence of males; 1.6:1.0) and Mourão (1:1). These results also differed from those found by Nunes & Hartz (2006), who reported the predominance of females in the populations of the congeners O. jenynsii and O. robustus at Fortaleza lagoon, State of Rio Grande do Sul, Brazil. Vazzoler (1996) commented that distinct environmental conditions (particularly food supply) would be reflected in distinct rates of mortality and/or growth for females and males, resulting in variations, both in the sex ratio among the different length classes and for the population as a whole.…”

“…12,no. 1 Tesch 1978, Goulart 1994, Godinho 1997, Peck et al 2005, Nunes & Hartz 2006. The proposed limit values usually vary between 2.5 and 4.0 according to Pope & Kruse (2007) or between 2.0 and 4.0 according to Bagenal & Tesch (1978).…”

“…The information available on the diet of Oligosarcus species, such as O. hepsetus (Deus & Petrere Junior 2003, Araújo et al 2005, Botelho et al 2007, O. jenynsii (Nunes & Hartz 2006), O. longirostris (Gealh & Hahn 1998, Loureiro-Crippa & Hahn 2006, O. pintoi (Meschiatti 1995, Castro & Casatti 1997, O. planaltinae (Luz- Agostinho et al 2006) and O. robustus (Nunes & Hartz 2006) characterized the prevalence of piscivory, with the feeding spectrum including an expressive variety of aquatic and/or terrestrial invertebrates, especially insects and decapods. The composition of the diet of O. paranensis in both studied reservoirs was similar to the feeding pattern of the above mentioned congeners, with fishes featuring as the main consumed resource.…”

“…Natural habitats with recorded Oligosarcus species include low order streams (Teixeira 1989, Castro & Casatti 1997, Vono et al1997, Deus & Petrere Junior 2003 and lagoons, including coastal lagoons (Hartz et al 1996, Nunes & Hartz 2006, Garcia et al 2007) and floodplain lagoons (Meschiatti 1995, Sosnovsky & Quirós 2009.…”

Crescimento e mortalidade de Oligosarcus hepsetus (Cuvier, 1829) (Characiformes, Characidae) no Parque Estadual da Serra do Mar, Núcleo Santa Virgínia, São Paulo, Brasil

“…Estudos envolvendo aspectos reprodutivos de espécies do gênero são encontrados nos trabalhos de Neves et al (1995), Hartz et al (1997), Fialho et al (1998), Hermes-Silva et al (2004) e Nunes et al (2004). A dieta foi investigada por Hartz et al (1996) e Nunes & Hartz (2006); e o crescimento de Oligosarcus jenynsi por análise e contagem dos anéis etários Hartz & Barbieri (1995).…”