Liu, H., McCaughran, D.A., Stickney, R.R., Kaimmer, S., Rust, M.B.
Abstract:
Pacific halibut (Hippoglossus stenolepis) is one of the most valuable
species for both commercial and sport fishing in North America.
Interest in halibut culture research is growing in many countries
because of its high market value. In the U.S., interest in halibut
aquaculture was initiated by the International Pacific Halibut
Commission (IPHC), which considered the possibility of releasing
juveniles for stock enhancement. The IPHC has tagged over 350,000
halibut since 1925 and 35,000 tagged fish have been recovered.
Tagging data show that a significant number offish stay within 100
km of the release area. A recent study conducted by the National
Biological Service reports that a substantial number of halibut remain
within a home-range.
It takes at least three years to establish a healthy halibut broodstock.
After capture, first-year survival rates are moderate, between 30 to
60%. Small fish, 50-70 cm, start feeding in two weeks while large
fish, over 120 cm, usually fast for several months. During the second
year in captivity, some medium (about 100 cm) females start
spawning. Egg quality is usually poor for the first-year spawners.
During the third year, second-year spawners usually produce good
quality eggs. Obtaining milt from male halibut is not a problem.
As a cold-water species, halibut prefer temperatures between 3 C and
8 C. High water temperatures adversely affect spawning quality.
Records show that during warm years, spawning was delayed and
gamete quality was low. Extreme warm weather in 1995 delayed
spawning by two months. Preliminary data from an ongoing trial
indicate that the upper lethal temperature for the first-year adult
halibut is about 13 C. At that temperature, 80% of the fish died within
the first three months of capture while 80% of the fish survived in
chilled water (11 C).
High water temperatures did not significantly affect feeding of
acclimated adult halibut during a one year test period in which
temperature fluctuated between 7.5 C and 13 C. Fish fed vigorously
in both summer and autumn. Feeding slowed when temperature
declined below 8 C. During the spawning season, males and immature
females fed moderately while mature females fasted until all eggs
were released. During a one year cycle, from April 1995 to March
1996, 25 adult halibut consumed about 700 kg of food including
frozen herring (60%), squid (12%), salmon (3%), and moist pellets
(25%). On the average, each fish needed about 80 g food per day. The
feeding rates varied between 1% (summer and autumn) and 0.1%
(winter and early spring) of body weight per day.
Adult halibut disliked dry commercial diet, but accepted moist pellets
that included 20% (dry basis) ground herring or some chemical
stimulants. Adult halibut growth rate increased 250% by rotating
feeding moist pellets with herring and squid. Before 1994, halibut
were fed only on herring and squid. The best growth rate then was
0.68% per day. Under the new feeding regime, similar size fish grew
to about 100 cm from about 75 cm within 18 months with a growth
rate of 1.88% per day.
(International Pacific Halibut Commission, P.O. Box 9005, Seattle,
Washington 98145, USA)