Program and Abstracts(PDF)

Presentation 22
TECHNIQUES FOR CURRENT CONTROL IN TANK; LESSONS LEARNED FROM
REARING LARVAE OF RED SPOTTED GROUPER Epinephelus akaara
Takashi Iwasaki *1 , Masatsugu Takano 2 , Kazuhisa Teruya 3
1 Stock Enhancement Technology Development Center, National Research Institute of
Aquaculture, FRA, Saiki, Oita 879-2602, Japan
2 Research Management Department, Headquarters, FRA, Minato-Mirai, Nishi-ku, Yokohama
220-6115, Japan
3 Stock Enhancement Technology Section, Ishigaki Tropical Station, Seikai National Fisheries
Research Institute, FRA, Fukai-Ohta, Ishigaki, Okinawa 907-0451, Japan
* Email: tak0829 at affrc.go.jp
Mass mortality of the early larval-stage (from hatch to about 10 days after hatching) has been one
of the big constraints during the process of mass fry production in groupers (Epinephelus bruneus,
E. septemfasciatus), bluefin tuna (Thunnus orientalis) or amberjacks (Seriola dumerili, S.
quinqueradiata). A phenomenon associated with the mass mortality is observed that early stage
larvae sink to and pile onto tank bottom, and the phenomenon, so called “sinking death
syndrome”, has been supposed to be one of the causes of the mass mortality. Many marine fish
appear to show ontogenetic change of larval body density, and it is speculated that body density
and swimming activity of larvae and current condition of rearing tank mutually influence on the
incidence of sinking death. It is indicated that proper current condition is important to prevent the
sinking death syndrome, and aeration, submersible pump and/or wave-making device have been
practically examined to make the current proper.
In the present study, rearing experiments were conducted in 60 m 3 tanks to investigate the
effects of current control by aeration volumes for preventing the sinking death syndrome of red
spotted grouper larvae. The aeration was done through four porous air hoses (1.5 m in length, 25
mm in diameter) that were set on the tank bottom along the lower edge of each wall. Larvae were
reared different aeration rates (0.25-1.50 L/min/tube), and the distribution, feeding amount,
survival and growth of larvae were determined. Larvae in the tank with aeration rate of 0.25
L/min/tube showed clearly the sinking performance to tank bottom. Larvae with aeration rate of
1.50 L/min/tube were not remarkably distributed in the lower layer, showing the best survival
without any differences in growth and feeding amounts from larvae in the other treatments. Thus,
the present results clearly show that physical environments such as water current inside tanks are
crucial factors to the improvement of survival and consequently the establishment of stable/mass
fry production technologies in groupers.
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