331
by set net is estimated to be 1:1 (Ueta and Jo 1989). Precise statistical data for
the total landing of S� lessoniana from all Japanese waters are not available. Ueta
(1992) estimated the annual S� lessoniana catch per year in the coastal waters of
Tokushima Prefecture, where S� lessoniana is abundant, to be 37–57 t by set net and
8–24 t by jigging (resource from 1985 to 1988). Based on 13 years of survey data
(resource from 1984 to 1996), Ueta (2000a) estimated the annual catch per year for
this squid in Tokushima Prefecture to be 79.1 ± 44.1 t.
Because squid caught by set nets can be kept alive and in good condition in net
cages, set nets are suitable for supplying live specimens, at a relatively high price, to
traditional Japanese restaurants and sushi bars. Squid caught by set net are also suitable for broodstock maintenance and aquaculture. Ikeda et al. (2004) transported
young and subadult S� lessoniana from set nets and reared them as the origin for culture trials. The approximately 740-km transfer took 22–23 h, and both water quality
and temperature had decreased by arrival (pH < 7.0, NH 4 -N 5.0 mg·L
−1
, temperature
> 4 °C). Squid survival is high when the BW to seawater volume ratio is below 30
at shipping. Survival is also relatively high in large containers, such as Styrofoam
boxes with large (> 1,620 cm
2
) bottom areas. An acclimation period of suitable duration is necessary when transported squid are moved to new aquaria. Squid with a
short acclimation (< 1 h) period die soon after being transferred to the aquaria, but
those with a longer acclimation (> 2 h) can survive (e.g. shipping container water
differs from aquarium water by 5 °C and 1.2 pH units).
Set nets also act as a spawning bed for S� lessoniana. Therefore, it is easy to get
freshly laid egg capsules for use in aquaculture. Three types of artificial S� lessoniana spawning beds were examined in the spawning grounds in the coastal waters
of Tokushima in Japan (Ueta et al. 1995; Ueta and Kitakado 1996). These were
fibreglass-reinforced plastic (FRP) type, mid-water cage type, and steel type. The
FRP type consisted of 9- or 12-mm-diameter FRP that were spaced 5, 10, 15, or
20 cm apart in 1 × 1 × 0.5 m concrete blocks. The mid-water cage type consisted of
0.5-, 1-, or 2-m-high cylindrical cages with a 9-mm rope that was stretched between
the walls, which were linked to three other cages, a float, and a concrete block. The
steel type consisted of 49 vertical and 0–6 horizontal 19-mm steel poles fixed to a
1 × 1 × 0.5 m concrete block (Ueta et al. 1995; Ueta and Kitakado 1996). Egg capsules were laid by S� lessoniana on these artificial spawning beds with the number
of egg capsules laid on FRP type > mid-water cage type > steel type. However,
the differences between the numbers of eggs laid on each spawning bed type were
small. When using the FRP-type spawning bed, female squid spawn many more
egg capsules on poles set close together than on poles that are widely spaced. Furthermore, female squid prefer spawning on these artificial spawning beds to natural
spawning beds composed of Sargassum and Zostera.
Late-stage egg capsules can be collected in order to decrease the necessary
incubation time and to avoid cessation of embryonic development at earlier stages
in captivity. However, special care must be taken when late-stage egg capsules are
collected because accidental pre-hatching often occurs due to physical shock during
transportation.
The availability of artificially fertilized eggs would be convenient for both
culture programs and experimental studies. Techniques for artificial insemination
17 Sepioteuthis lessoniana
by set net is estimated to be 1:1 (Ueta and Jo 1989). Precise statistical data for
the total landing of S� lessoniana from all Japanese waters are not available. Ueta
(1992) estimated the annual S� lessoniana catch per year in the coastal waters of
Tokushima Prefecture, where S� lessoniana is abundant, to be 37–57 t by set net and
8–24 t by jigging (resource from 1985 to 1988). Based on 13 years of survey data
(resource from 1984 to 1996), Ueta (2000a) estimated the annual catch per year for
this squid in Tokushima Prefecture to be 79.1 ± 44.1 t.
Because squid caught by set nets can be kept alive and in good condition in net
cages, set nets are suitable for supplying live specimens, at a relatively high price, to
traditional Japanese restaurants and sushi bars. Squid caught by set net are also suitable for broodstock maintenance and aquaculture. Ikeda et al. (2004) transported
young and subadult S� lessoniana from set nets and reared them as the origin for culture trials. The approximately 740-km transfer took 22–23 h, and both water quality
and temperature had decreased by arrival (pH < 7.0, NH 4 -N 5.0 mg·L
−1
, temperature
> 4 °C). Squid survival is high when the BW to seawater volume ratio is below 30
at shipping. Survival is also relatively high in large containers, such as Styrofoam
boxes with large (> 1,620 cm
2
) bottom areas. An acclimation period of suitable duration is necessary when transported squid are moved to new aquaria. Squid with a
short acclimation (< 1 h) period die soon after being transferred to the aquaria, but
those with a longer acclimation (> 2 h) can survive (e.g. shipping container water
differs from aquarium water by 5 °C and 1.2 pH units).
Set nets also act as a spawning bed for S� lessoniana. Therefore, it is easy to get
freshly laid egg capsules for use in aquaculture. Three types of artificial S� lessoniana spawning beds were examined in the spawning grounds in the coastal waters
of Tokushima in Japan (Ueta et al. 1995; Ueta and Kitakado 1996). These were
fibreglass-reinforced plastic (FRP) type, mid-water cage type, and steel type. The
FRP type consisted of 9- or 12-mm-diameter FRP that were spaced 5, 10, 15, or
20 cm apart in 1 × 1 × 0.5 m concrete blocks. The mid-water cage type consisted of
0.5-, 1-, or 2-m-high cylindrical cages with a 9-mm rope that was stretched between
the walls, which were linked to three other cages, a float, and a concrete block. The
steel type consisted of 49 vertical and 0–6 horizontal 19-mm steel poles fixed to a
1 × 1 × 0.5 m concrete block (Ueta et al. 1995; Ueta and Kitakado 1996). Egg capsules were laid by S� lessoniana on these artificial spawning beds with the number
of egg capsules laid on FRP type > mid-water cage type > steel type. However,
the differences between the numbers of eggs laid on each spawning bed type were
small. When using the FRP-type spawning bed, female squid spawn many more
egg capsules on poles set close together than on poles that are widely spaced. Furthermore, female squid prefer spawning on these artificial spawning beds to natural
spawning beds composed of Sargassum and Zostera.
Late-stage egg capsules can be collected in order to decrease the necessary
incubation time and to avoid cessation of embryonic development at earlier stages
in captivity. However, special care must be taken when late-stage egg capsules are
collected because accidental pre-hatching often occurs due to physical shock during
transportation.
The availability of artificially fertilized eggs would be convenient for both
culture programs and experimental studies. Techniques for artificial insemination
17 Sepioteuthis lessoniana