Effects of acclimation to the natural environment
before release on retention rate, feeding condition and predation of
hatchery-reared juveniles of the coral trout Plectropomus leopardus
released on a coral reef
K.
Hamasaki, H. Takeuchi, S. Shiozava, K. Teruya-2004
Nippon
Suisan Gakkaishi, 70(1): 22-30
Abstract:
Retention
rate, feeding condition and predation of hatchery-reared juveniles of the
coral trout Plectropomus leopardus released on a coral reef in
Urasoko Bay, Ishigaki Island were investigated to evaluate the effectiveness
of acclimation of juveniles to the natural environment before release. Two
experiments were conducted and 2000 juveniles [mean total length (TL), 137
mm] and 900 juveniles (mean TL, 79 mm) were stocked in a net cage (400 m2)
which was set on the release site in the first and second trials,
respectively. After acclimation for 7 days in the net cage, acclimated
juveniles (test group) were released with the control groups of 2000
juveniles (mean TL, 142 mm) in the first trial and 900 juveniles (mean TL,
86 mm) in the second trial. Test and control groups were distinguished by
different color tags. The second release experiment could not be conducted
satisfactorily due to a typhoon. Judging from the feeding incidence, changes
of condition factor and visceral weight index of juveniles after release in
the first trial, it was considered that juveniles of the test group were
more acclimated to the natural environment than those of the control group.
Furthermore, juveniles of the test group tended to be less vulnerable to
predation by piscivorous animals than those of the control group due to the
improvement of behavior of lurking in the coral rubble.
(Yaeyama
Station, National Center for Stock Enhancement (NCSE), Ishigaki, Okinawa
907-0451, Japan)