Nursery culture of the abalone Haliotis laevigata: Larval settlementand juvenile production using cultured algae or formulated feed

摘要

This study was conducted to investigate the settlement, growth, survival, and size variability of the abalone Haliotis laevigata on commercial scale. At settlement, two plate conditioning times for the green alga Ulvella lens (conditioned for 6 or 8 wk) were evaluated and compared with plates colonized by different diatom species (Navicula cf. jeffreyi and Cocconeis sp.). In a choice experiment an overall settlement rate of 87% was estimated 3 days after larval release. The majority of the larvae chose to settle on U. lens (61% on 8-wk-old and 14% on 6-wk-old U. lens, with average algal cover of 97% and 82% respectively). Larvae showed a clear preference for older than for younger U. lens, with similar percentage cover, indicating that the developmental stage of the alga and not percentage cover per se is important in settlement induction. Only 7% and 5% respectively of the settled larvae were found on the plates colonized by the diatom species N. cf. jeffreyi and Cocconeis sp. Results clearly demonstrate that U. lens provides a suitable substrate to improve the settlement of Haliotis laevigata larvae on commercial scale. Juvenile growth ( mu m day super(-1)) on a mixed diet of U. lens and N. cf. jeffreyi was not constant and increased with size to 70-80 mu m day super(-1). Both growth rate and size variability increased over time until juveniles reached approximately 5 mm in shell length. The survival declined to ca. 30% at 44 days after settlement but stabilized thereafter. Distinct increases in size variability were observed between 3 and 16 and between 30 and 44 days after settlement, followed by elevated growth rates and a change from monomodal to multimodal distribution at day 44. The latter coincided with a shift in diet from a diatom-dominated diet to a macroalgal diet of U. lens at day 44. The increase in growth rate between 3 and 16 days is believed to reflect a shift in nutrition with postlarvae switching from absorbing yolk reserves to efficient exogenous feeding. The growth, survival, and size variability of juveniles was assessed when feeding on algal diets as well as a formulated diet. Juveniles grew faster on U. lens than on a formulated feed or plates colonized with the diatom N. cf. jeffreyi. Results indicate that growth of juveniles may be more variable when feeding on natural feed (Navicula cf. jeffreyi., U. lens) than on a formulated feed. However, until a feed is formulated that can match the mean growth rates achieved on U. lens, we suggest keeping juveniles on plates colonized with U. lens as long as possible. Juvenile H. laevigata should not be weaned onto formulated feed until they reach at least 5 mm in shell length.