Testing various substances that have been bound to plastic plates with agar to induce larval settlement and metamorphosis of abalone Haliotis discus discus (Reeve)

摘要

An experimental culture system was developed as an alternative to diatom biofilms for settling larval abalone and on-growing the resulting post-larvae. The system is designed to allow artificial micro-particulate food to be sprayed (continuously until abalone are capable of feeding on seaweed) onto bard corrugate plastic plates, using agar as a fixative. Two trials were conducted to test substances that could be utilized to improve the settlement and metamorphosis rate of larval Haliotis discus discus when using the above experimental system. In trial 1, plates were sprayed with a mixture containing 1% agar and one of the following: natural diatom powder, Spirulina powder, Chlorella powder and two different concentrations of gamma-aminobutyric acid (GABA), each with and without antibiotics. The negative control was a clean plastic plate without any additives and the positive control was plastic plates covered with a living natural diatom biofilm. There was no significant difference in the final metamorphosis rate of larvae induced to settle on the three microalgal powders and the positive control (25.8-35.8%). However, these treatments had a significantly higher larval metamorphosis rate when compared to the negative control and the GABA treatments (1.7-7.5%). GABA did not induce metamorphosis of larvae at a significantly higher rate than the negative control, regardless of whether antibiotics were used or not. In trial 2, the effect of using both algal powders and mucus was tested to determine settlement and metamorphosis rates of larval abalone. Combining the effects of mucus and micro-algal powders or the positive control and mucus resulted in a final larval settlement rate of 80.8-89.2% and metamorphosis rate of 73.3-87.5%. This was significantly higher than the treatments that only incorporated micro-algal powder or the positive control, having an attachment rate of 20.8-41.7% and a total metamorphosis rate of only 3.3-28.3%. There is potential to use micro-algal powder as a substitute to living diatoms, to act as a settlement cue for larval H. discus discus. Abalone mucus should also be used in addition to microalgal powders to increase the settlement rate of larvae and also ensure a high rate of metamorphosis