Estrutura populacional, biologia reprodutiva e ecologia alimentar de Loricariichthys melanocheilus Reis & Pereira, 2000 (Siluriformes, Loricariidae) no rio Ibicuí, RS, Brasil

Abstract

The aim of this work was analyze population structure, reproductive biology and feeding ecology of Loricariichthys melanocheilus in Ibicui River. Fish were caught bimonthly in lotic and lentic environment between São Vicente do Sul and Itaqui, with gillnets and witches, with revision every six hours. The population structure was evaluated by seasonal and spatial distribution, bimonthly variations in average size, sex ratio and weight-length relationship. Females reached larger sizes than males and the sex ratio was 1.38 females per male, with some variations bimonthly. This species showed positive allometric growth, with greater increase in weight than in length during ontogenetic development. The condition factor was higher in males and in June/July. Females didn t show variations in this parameter. The values of gonad condition factor, GSI and the frequency of mature individuals indicate that the reproductive period begins in August/September, peaking in October / November and spawning in the following months. Regarding the feeding ecology, L. melanocheilus showed a detritivorous feeding habit, even consuming sediment, organic vegetable matter, nematodes, insects of the order Diptera, Trichoptera, Ephemeroptera and Odonata, algae, microcrustaceans, fungi, protozoa and other invertebrates. The diet showed little seasonal, environmental and by length classes variation. The species showed no intense feeding activity, being higher before or after the reproductive period and in lentic environment. The intestinal quotient of 1.51 was smaller than registered for other species of the family, showing variations according to the length classes in response to variations in the diet.