T. Kawamura, R.D. Roberts, H. Takami
Abstract:
Survival and growth of abalone postlarvae are greatly influenced by food quality and quantity. Abalone larvae settle on coralline algae, some diatoms films, and conspecific mucous trails. These substrata provide a wide range of potential food sources, which are used in different ways as postlarvae develop. We identify three major transitions in feeding and growth: (1) at metamorphosis, a shift from lecithotrophy/dissolved organic matter (DOM) absorption to particle feeding, with an overlap in nutrition sources; (2) at about 600-800 mu m shelf length (SL), postlarvae become responsive to the "digestibility'' of diatom diets and grow more rapidly on efficiently digested strains; (3) at around 5-10 mm SL juveniles shift from a biofilm-dominated diet to a macroalgae-dominated diet. We can make some tentative generalizations about growth rates of postlarvae fed ingestible diatoms. Rapid growth (20-30 mu m/day) in the first 10 days postsettlement often falls to 10-20 mu m/day in the following 1-2 wk, perhaps reflecting the exhaustion of nutrition from yolk/DOM. Postlarvae of 0.8-2 mm SL grow similar to 40-60 mu m/day on "digestible" diatoms and 15-30 mu m/day on "indigestible" ones. Rapidly growing juveniles over 3 mm SL will grow at 100 mu m/day or more, whereas poor diets can halve these growth rates. Growth rates of individual abalone will vary widely on both good and poor diets. Diatoms that are emerging as key species for abalone culture include Cylindrotheca closterium land needle-shaped Nitzschia spp.), Cocconeis spp., and Achnanthes spp., but caution is needed in extrapolating from the limited data available. Hatcheries need to maintain a suitable quantity of ingestible food as well as consider food quality. Many aspects of postlarval feeding and growth require further research.
(Tohoku Natl Fisheries Res Inst, 3-27-5 Shinhama, Shiogama, Miyagi 9850001, Japan)