Browsing by Author "CACERES, CW"

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    DIGESTIVE MECHANISMS IN APLODACTYLUS PUNCTATUS (VALENCIENNES) - A TEMPERATE MARINE HERBIVOROUS FISH
    (1995) OJEDA, FP; CACERES, CW
    The herbivore Aplodactylus punctatus (Valenciennes) is one of the most abundant fish species inhabiting the rocky subtidal coast of central Chile. To determine the mechanisms of algal digestion in this species, we investigated the pH pattern along the digestive tract, and its relation to feeding frequency, the occurrence of enzymes capable of hydrolizing cellulose and other related polymers of the algal cell wall, and the distribution and activity of digestive enzymes. Specimens of A. punctatus were collected in 1989 and 1992 from 2 localities of the central Chilean coast. Measurements of pH and enzymatic assays were carried out on samples of the contents of the stomach, and of the anterior, middle, and posterior portions of the intestine. Both the diet and the gastrointestinal pH pattern showed no differences between day and night. The stomach was highly acidic (pH 2.1 to 2.6), whereas the intestine was slightly alkaline (pH 6.6 to 7.8). No enzymatic activity was detected along the digestive tract for the assayed carragenans, agar, and alginates. Cellulase and amylase were found in the intestine but were not present in the stomach. Both enzymes showed the greatest activity in the anterior intestine. Protease (probably pepsin) was mainly found in the stomach. The increased acidity of the stomach, and the cellulolytic activity of the intestine - likely due to microorganisms - strongly suggests that a combination of acid hydrolysis and enzymatic digestion of algal cell wall, followed by digestion of carbohydrates and proteins, would explain the high assimilation rates of plant material reported for this species.
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    OPTIMAL FEEDING STRATEGY OF THE TEMPERATE HERBIVOROUS FISH APLODACTYLUS-PUNCTATUS - THE EFFECTS OF FOOD AVAILABILITY ON DIGESTIVE AND REPRODUCTIVE PATTERNS
    (1994) CACERES, CW; FUENTES, LS; OJEDA, FP
    In this study we examined differences in feeding behavior of populations of the marine temperate herbivorous fish Aplodactylus punctatus, in three different localities off the Chilean coast, which differ qualitatively and quantitatively in food availability. We test whether food selection follows optimal foraging strategies, whether there is any modification of the fishes' digestive tracts in relation to their diets, and whether differences in diet quality affect the allocation of energy into reproduction and maintenance in these populations. Samples of this fish and of the understore algal assemblages were taken seasonally from May 1989 to February 1990. For each population we analyzed dietary composition, weight of the digestive tract and of the food content, the condition factor (K), and the gonadosomatic index (GSI). Our results showed that the diet observed in the three populations closely resembled the differences in macroalgal abundance and composition among the three localities studied. Local differences in diet quality were inversely related to the amount of food consumption and size of the digestive tract, suggesting that under differential conditions of food availability A. punctatus is able to compensate for variations in food quality through a flexibility in its digestive strategies. The nutritional status (K) of individuals, and their reproductive pattern (GSI) were directly related to diet quality. These results indicate that although A. punctatus is able to adjust its digestive processes to different algal food regimes, the digestive modifications observed in food-poor environments are not sufficient to compensate for the lack of food and allow fish to reach the nutritional status and reproductive output reached in a food-rich environment. This study represents the first natural experiment demonstrating a direct relationship among food availability, feeding patterns, digestive processes, and reproductive effort.