Radula development in abalone Haliotis discus hannai from larva to adult in relation to feeding transitions

Abstract

The radula morphology of Haliotis discus hannai was examined by scanning electron microscope from the larval to the adult stage. The radula of competent larvae contained 11–13 transverse rows of teeth after 6–7 days at 20°C. The number of rows increased to 25–30 during the first several days after settlement, but then remained approximately constant throughout the post‐larval period, increasing again in abalone larger than 4 mm in shell length (SL). In post‐larvae < ~1 mm SL, only two pairs of lateral teeth (L1, L2) were present in the larval radula. An additional three pairs of lateral teeth (L3–L5) were added progressively as post‐larvae grew from 0.9 mm to 1.9 mm SL. Marginal teeth were added steadily from one pair in larvae to 30–40 pairs at 3–4 mm SL, 70–80 pairs in 30–40 mm juveniles, and 70–90 pairs in 90–100 mm adults. The serrations on the working edges of the rachidian (R) and lateral teeth became less pronounced as the abalone grew. Nearly all serrations disappeared from the rachidian (R) and inner lateral teeth (L1, L2) by ~2 mm SL, and from the outer lateral teeth (L3–L5) by 20 mm SL. For abalone larger than 1.5 mm SL, the L3–L5 teeth became longer and more pointed, which increased the space between adjacent rows of teeth. Post‐larvae < 1 mm SL had highly curved teeth with clearance angles of approximately or less than zero, whereas larger abalone had positive clearance angles. These radula developments appear to be related to transitions in feeding habits from microbial to macroalgal diets.

Suitability of two seaweeds, Gracilaria lemaneiformis and Sargassum pallidum, as feed for the abalone Haliotis discus hannai Ino

“…The morphological structure of the radula allows H. discus hannai to graze the blades of L. japonica more effectively than the filamentous seaweeds G. lemaneiformis and S. pallidum (Kawamura et al, 2001;Nie and Yan, 1985). The low feed intake of S. pallidum may be caused by the toughness of the stipe.…”

Reproduction and Early Life Ecology of Abalone Haliotis diversicolor in Sagami Bay, Japan

“…When post-larval abalone attain to ~1.8 mm SL, they are able to efficiently utilize juvenile macroalgae 41 . These transitions in the feeding habit are closely associated with ontogenetic changes in the digestive enzyme activity 36 and in the radula morphology 10 . Ontogenetic changes in the radula morphology of H. diversicolor are similar to those of H. discus hannai, suggesting that similar feeding transitions occur in H. diversicolor in early life stages 23 .…”

Dietary value of gametophytes and juvenile sporophytes of the brown macroalga Eisenia bicyclis for juvenile abalone Haliotis diversicolor

“…Once postlarval abalone reach about 2 mm SL, they are able to utilize juvenile macroalgae efficiently [15,16]. These transitions in feeding habits are closely associated with ontogenetic changes in digestive enzyme activity [17] and in radula morphology [18]. However, the feeding transitions in early life stages have not been verified for most abalone species.…”