The size to which abalone, Haliotis discus hannai, is able to grow on attached microalgae as a sole dietary source in deep seawater (DSW; seawater below the euphotic layer) using continuous and simultaneous culturing system was investigated in this study. A transparent 12 cm (diameter)×50 cm (length) acrylic column containing many short-cut vinyl tubes of 3 cm (diam.) and 3 cm (length) as substrata, was used. DSW pumped from 320 m depth at Muroto City, in Kochi Prefecture, Japan, was supplied continuously and then incubated under natural light conditions (ca. 4,500 lx). After growing a sufficient number of attached microalgae in the columns, 1-year-old abalone Haliotis discus hannai juveniles with an average shell length of ca. 2.2 cm were placed into the column and reared simultaneously with attached food microalgae in the continuous DSW-_ow system. During the 260-day rearing process, the juveniles grew up to 3.5‒4.3 cm. Daily growth rates were around 60‒80 μm d－1, and sometimes over 100 μm d－1. These results indicate that abalone H. discus hannai can grow up to at least 4 cm shell size on attached microalgae as the sole dietary source without any supply of seaweed or pellet food. This suggests that the continuous culturing of attached microalgae and simultaneous rearing of juvenile abalone using nutrient-rich DSW will be a possible culturing system without any feeding cost.

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