Browsing by Author "Aldana, M"

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    Does food quality influence thermoregulatory behavior in the intertidal fish Girella laevifrons?
    (2003) Pulgar, JM; Aldana, M; Bozinovic, F; Ojeda, FP
    Algal and invertebrate species are less abundant towards higher zones of the intertidal, where the greatest variations in physical environmental conditions occur. Mobile predators such as fishes that inhabit high intertidal rockpools are thus exposed to wide variations in physical conditions and to a low abundance and quality of food. We used an aquarium with a temperature gradient in the laboratory to assesed whether dietary quality differences modify temperature preferences of Girella laevifrons, one of the most abundant transitory fishes inhabiting rocky shores along the coast of Chile. Our results indicate that food quality clearly modifies temperature preferences in this species. Animals fed on high quality bivalves selected intermediate temperatures (16-18degreesC) while those fed on lower quality algae selected lower temperatures (10-12degreesC). Control fish not subjected to the temperature gradient did not select portions of the aquarium differentially. The thermal selectivity of G. laevifons in relation to the optimization of digestive processes and mechanisms of energy conservation are discussed. (C) 2003 Elsevier Ltd. All rights reserved.
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    Morphometric and parasitological evidence for ontogenetic and geographical dietary shifts in intertidal fishes
    (2002) Aldana, M; Pulgar, JM; Ogalde, F; Ojeda, FP
    Studies on the feeding ecology of intertidal fish assemblages have indicated the existence of three trophic groups: herbivores, omnivores and carnivores. This classification has enabled researchers to establish some ecological relationships among their components. However, temporal and spatial variations in the use of food resources have rarely been addressed. In this study, ontogenetic and geographical variations in the diet of two inter-tidal fish species: Girella laevifrons and Graus nigra were evaluated through an integrative analysis of their diet, relation between intestinal length/body length, and their parasite fauna. Results of this combined analysis suggest ontogenetic and geographical variations in the diet of G. laevifrons. In G. nigra, no evidence of ontogenetic dietary shifts was found, but marked differences in diet were detected among localities. However, parasitological evidence does not reflect the geographical differences in its diet. Omnivory of G. nigra at two localities (viz Caleta Errazuriz and El Tabo) may be indicative of the opportunistic nature of this species related to the greater availability of macroalgae at these localities. The assessment of intestinal length of G. nigra highlights the importance of considering macroalgal species composition, and not only their abundance as a group, when estimating the quality of the diet of a given fish species. In general, the geographical differences in diet, length of the intestine and parasitofauna of G. laevifrons and G. nigra together suggest that a species' diet is a dynamic feature that may be related to variations in the availability of food resources in the environment.