Settlement and early growth of abalone larvae Haliotis asinina linnaeus, in response to the presence of diatoms

Abstract

GABA (gamma-aminobutyric acid) of different concentrations (10 -6, 10-5, 10-4, 10-3 M) was tested for its effects on the settlement response of abalone Haliotis asinina larvae of 48 hours old. The highest percentage (73.5%) of attachment was found in larvae reared in seawater containing 10-6 M GABA. In addition, five benthic diatom species (Navicula sp. 1, Navicula sp. 2, Navicula sp. 3, Nitzschia sp. 1, and Nitzschia sp. 2) were isolated and maintained in culture. The species were grown in small bowls and tested in settlement experiments with H. asinina larvae. Settlement was very high in 2-day-old larvae fed five species of diatoms (89.8-94.3%). Survival rates declined when the larvae were older (6-7 days). The highest percentages of metamorphosis and shell growth were found in larvae fed Navicula sp. 1, Nitzschia sp. 2, and Navicula sp. 1. A flow-through system in large fiberglass tanks was developed to compare growth and survival of postlarvae reared on diatoms, Navicula sp. 1, Navicula sp. 2, and Nitzschia sp. 1 for 120 days. The shell length (SL) and weight (W) of postlarvae were measured once every 2 weeks. The best growth rate was obtained with postlarvae fed Nitzschia sp. 1 (SL 81.7 μm/day, W 96.7 μg/day) and Navicula sp. 2 (SL 75.0 μm/day, W 78.3 μg/day).