|Abalone: we need our space!|
|For abalone to grow well, low stocking rate is good, high stocking bad, and reduced oxygen downright ugly|
|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.
A SEAFDEC/AQD study suggests that fruits peels can be used as additives for tilapia feed.