Composition, size and relative density of diatoms in the stomach of 4 to 75 day-old juvenile abalone Haliotis diversicolor (Reeve)

Abstract

The diatom biofilm that naturally grow on polyvinyl chloride plates serve as food of postlarva and juvenile abalone Haliotis diversicolor Reeve, called “tokobushi” in Japanese. Composition, size and relative density of diatoms in the stomach of 4, 7, 10, 13, 17, 21, 27, 35, 50 and 75 day-old tokobushi were evaluated to characterize their diatom intake. Stomach in glycol methacrylate resin was sectioned and examined under the light microscope, then analyzed using an image processing software. The diatoms present in the stomach of tokobushi were Thalassiosira, Melosira, Triceratium, Odontella, Asterionella, Licmophora, Thalassionema, Cocconeis, Navicula and Nitzschia. Only four varieties of diatoms were observed in 4 to 10 day-old tokobushi which coincided with initial feeding. The number and size of diatoms increased in 13 to 75 day-old juvenile, which were exhibited in its exponential growth pattern. The stomach of 4 to 13 day-old tokobushi contained small-sized diatoms (<67 µm) while both small and large-sized diatoms (>123 µm) were observed in 17 to 75 day-old juveniles. Higher relative densities (8.7 – 15.8 diatom/1000 µm2) of diatoms were documented in 4 to 10 day-old tokobushi while 17 to 75 day-old exhibited lower relative densities (1.2 – 4.2 diatom/1000 µm2). Generally, as young tokobushi increases in size, the diatom intake increases in composition and size but density decreases with increasing size of diatom ingested.