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As one of the major countries harvesting
abalone, the Philippines is mostly dependent on wild catch since
commercial grow-out system for Haliotis asinina is still a
pioneering effort. Due to the low profit margin in land-based culture
systems, alternative means such as sea cages are being pursued.
A study conducted by Emmanuel Capinpin Jr
and his colleagues determined the effects of different stocking
densities on the growth, feed conversion ratio (FCR) and survival of
abalone using the cage system. Employing three trials using different
stocking densities, the researchers raised abalone, with sizes ranging
from 16-20 mm and 35-40 mm in 40 x 40 x 20 cm net cages suspended from
floating rafts at SEAFDEC/AQD’s marine substation in Guimaras, west
central Philippines. The abalone were fed the red alga Gracilariopsis
bailinae.
The trials, which lasted for as long as 180
days, were consistent in one aspect: regardless of time period, there
were no significant differences in the survival rate and FCR. However,
the study did show that daily growth rates in both weight and height
were higher in cages with lower stocking density.
Why the difference? The study suggests that
there is an inverse relationship between growth and stocking density,
which means that the lower the stocking density, the greater the growth
of the abalone. The cramped space causes the abalone to stack due to
lack of space for attachment, which in turn hinders their ability to
move and ingest food, thus, the lower growth rates. In addition,
increased levels of metabolic wastes and reduced dissolved oxygen, which
result from higher densities, also lead to poor growth. A balance
between stocking density and area for culture should be attained to
maximize profit.
Technology adopters will no doubt be
encouraged to venture into this endeavor once the results of the
economic analysis is found satisfying.
This research on sea cage culture of abalone
has been published in the journal Aquaculture (1999) 171: 227-235.
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