MEPS 118:37-42 (1995)  -  doi:10.3354/meps118037

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.

Herbivorous fish . Digestion . Enzyme activity . Acid lysis