February 15-18, 2009 Washington State Convention Center Seattle ...

PRACTICAL APPLICATION OF AN INTEGRATED LARVAL-NURSERY SYSTEM FOR THE
PRODUCTION OF CALIFORNIA HALIBUT, Paralichthys californicus
Kevin Stuart*, Michael Paquette, Keri Maull, Mark Drawbridge and Paula Sylvia
Hubbs-SeaWorld Research Institute
2595 Ingraham Street
San Diego, CA 92109 USA
kstuart@hswri.org
In order to reduce stress and mortality during transfer of larval California halibut immediately prior to settlement, we developed
a larval-nursery system that combined two of our preferred rearing vessel designs into one integrated, space-saving system
(Figure 1). The engineering aspects of this system were reported at WAS 2007. This paper reports on the first of three planned
rearing trials in this system.
Halibut eggs were collected from a 44 m 3 broodstock tank, maintained under ambient temperature and photoperiod conditions.
Egg quality parameters examined for this trial included egg viability (81.9%), hatch rate (84%) and survival to 1 st feeding
(91%). The eggs were placed into one of four 1600L black conical bottom tanks at a density of 100 eggs/L. The tanks were
maintained at 17.7 C (± 0.94 C) under ambient lighting (0 – 2200 lux) on an independent recirculating system. The flow to
each tank was set at 5 L/min.
Halibut larvae were reared in the cone tanks using traditional greenwater and rotifer and/or Artemia live feeds until 27 dph.
At 27 dph the pelagic larvae were transferred to an independent recirculating raceway system by selecting one of three 5 cm
transfer pipes that exited each cone tank at different elevations corresponding to one of three vertically stacked raceways. The
transfer process took approximately 1-2 days when transfer flows were set at 8 – 12 L/min, there were no observable effects
on fish health from transfer. Dry feed was introduced to the juveniles at 32 dph and weaning was complete by 45 dph. In the
raceways, water flow rates and depth were adjusted based on the stage of fish development from 10 – 90 L/min and 5.1-30.5 cm
deep. This created water velocities of 0.6 – 6.0 cm/sec. Water velocities were maintained at a relative rate of 1.0 to 1.5 body
lengths per second in order to facilitate self cleaning, and promote faster growth.
Halibut grew to 4.0 g by 96 dph. Survival from egg was 1.1 – 2.2% when evaluated for each raceway cohort. The percent of
malpigmented halibut was also high 20-30%. No disease outbreaks were observed. Overall the system worked very well and
as we had hoped. The most significant losses were due to aggression and cannibalism in the shallow raceways as pelagic larvae
were “harassed” by larger, settled siblings. Future rearing trials will incorporate aggressive grading protocols to minimize
these losses.
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