Testing various substances
that have been bound to plastic plates with agar to induce larval settlement
and metamorphosis of abalone Haliotis discus discus (Reeve)
A.E. Stott, T. Takeuchi, Y. Koike-2004
Aquaculture, 231(1-4): 547-557
Abstract:
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 hard 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 γ-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 micro-algal 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 micro-algal powders to increase the settlement rate of larvae
and also ensure a high rate of metamorphosis.
(Laboratory of Fish Culture, Department of Aquatic
Biosciences, Tokyo University of Fisheries, 4-5-7, Konan, Minato, Tokyo
108-8477, Japan, e-mail of T. Takeuchi: take@tokyo-u-fish.ac.jp)