342
acceptable form of artificial feed are still encountered (Nabhitabhata et al. 2001b;
Sangpradab et al. 1984).
Nursing and ongrowing in net cages and pens in situ should be studied as a
means of reducing the cost of S� lessoniana culture. At selected sites, such facilities
could substitute for land-based hatcheries. In tropical countries, such facilities must
be protected from strong sunlight, as excess lighting causes stress to cultured squid,
fouling of egg capsules, and fouling of cage cover nets.
Monosex culture may be a method for postponing reproduction and prolonging
squid growth. To accomplish this, squid must be separated by sex before proceeding
to, or as early as possible in, the ongrowing phase. The sex of S� lessoniana can be
determined from their colour patterns 60 days after hatching (Nabhitabhata 1978,
1983).
Manipulation of the sex ratio or artificial sex induction for S� lessoniana can increase production. The degree of sexual size dimorphism is high. S� lessoniana males
are much larger than females. Batch cultures with many large males will produce a
higher yield than cultures with few large males. Manipulation of the development of
the male external characters through the application of sex hormones, e.g. testosterone, is feasible. The methodology for this type of manipulation can be adapted from
that which is already used in the finfish culture industry for tilapia ( Oreochromis
niloticus) and groupers ( Epinephelus spp.). For example, developing S� lessoniana
egg capsules can be immersed in water that contains a particular hormone and/or the
young can be fed hormone-added feed. These methods need further study.
S� lessoniana is a complex species (Dunning 1998) comprised of at least three
morphs with different final sizes. Segawa et al. (1993a, b) reported morphological, behavioural, and ecological differences among three morphs of S� lessoniana
with the local names shiro-ika (white squid), aaka-ika (red squid), and kuwa-ika
(small squid) from Ishigaki Island of the Ryukyu Archipelago, Japan. The three
morphs have different final sizes, chromatophore arrangements, egg-capsule characteristics, spawning sites, and seasons (Izuka et al. 1996b; Segawa et al. 1993a, b).
Molecular evidence indicates genetic differences between the three morphs (Izuka
et al. 1994, 1996a; Yokokawa and Ueta 2000; Triantafillos and Adams 2005; Aoki
et al. 2008). Further investigation and taxonomic description are required to determine whether these differences are at the specific or subspecific level. Differences
in the growth rate of different morphs should be a very interesting research topic for
the maximization of aquaculture production.
Although S� lessoniana is widely distributed in the Indo-Pacific region, collection sites for materials (i.e. eggs) used for previous culture or long-term rearing are
predominantly located in Asian waters. For example, all of the S� lessoniana eggs
used by Lee et al. (1994); Forsythe et al. (2001), and Walsh et al. (2002) were collected from Asian waters, i.e. Thailand, Mainland Japan, and Okinawajima Island
of Japan. These Asian countries have major fisheries for this species (Ueta et al.
1992, 2000a; Chotiyaputta et al. 2002; Lu 2002). These countries are ideal locations
for studying the culture of S� lessoniana. Aquaculture facilities for cephalopods and
other marine organisms are already established in Asian countries. Squid cultured in
such facilities can be used as scientific experimental models, species for restocking,
J. Nabhitabhata and Y. Ikeda
acceptable form of artificial feed are still encountered (Nabhitabhata et al. 2001b;
Sangpradab et al. 1984).
Nursing and ongrowing in net cages and pens in situ should be studied as a
means of reducing the cost of S� lessoniana culture. At selected sites, such facilities
could substitute for land-based hatcheries. In tropical countries, such facilities must
be protected from strong sunlight, as excess lighting causes stress to cultured squid,
fouling of egg capsules, and fouling of cage cover nets.
Monosex culture may be a method for postponing reproduction and prolonging
squid growth. To accomplish this, squid must be separated by sex before proceeding
to, or as early as possible in, the ongrowing phase. The sex of S� lessoniana can be
determined from their colour patterns 60 days after hatching (Nabhitabhata 1978,
1983).
Manipulation of the sex ratio or artificial sex induction for S� lessoniana can increase production. The degree of sexual size dimorphism is high. S� lessoniana males
are much larger than females. Batch cultures with many large males will produce a
higher yield than cultures with few large males. Manipulation of the development of
the male external characters through the application of sex hormones, e.g. testosterone, is feasible. The methodology for this type of manipulation can be adapted from
that which is already used in the finfish culture industry for tilapia ( Oreochromis
niloticus) and groupers ( Epinephelus spp.). For example, developing S� lessoniana
egg capsules can be immersed in water that contains a particular hormone and/or the
young can be fed hormone-added feed. These methods need further study.
S� lessoniana is a complex species (Dunning 1998) comprised of at least three
morphs with different final sizes. Segawa et al. (1993a, b) reported morphological, behavioural, and ecological differences among three morphs of S� lessoniana
with the local names shiro-ika (white squid), aaka-ika (red squid), and kuwa-ika
(small squid) from Ishigaki Island of the Ryukyu Archipelago, Japan. The three
morphs have different final sizes, chromatophore arrangements, egg-capsule characteristics, spawning sites, and seasons (Izuka et al. 1996b; Segawa et al. 1993a, b).
Molecular evidence indicates genetic differences between the three morphs (Izuka
et al. 1994, 1996a; Yokokawa and Ueta 2000; Triantafillos and Adams 2005; Aoki
et al. 2008). Further investigation and taxonomic description are required to determine whether these differences are at the specific or subspecific level. Differences
in the growth rate of different morphs should be a very interesting research topic for
the maximization of aquaculture production.
Although S� lessoniana is widely distributed in the Indo-Pacific region, collection sites for materials (i.e. eggs) used for previous culture or long-term rearing are
predominantly located in Asian waters. For example, all of the S� lessoniana eggs
used by Lee et al. (1994); Forsythe et al. (2001), and Walsh et al. (2002) were collected from Asian waters, i.e. Thailand, Mainland Japan, and Okinawajima Island
of Japan. These Asian countries have major fisheries for this species (Ueta et al.
1992, 2000a; Chotiyaputta et al. 2002; Lu 2002). These countries are ideal locations
for studying the culture of S� lessoniana. Aquaculture facilities for cephalopods and
other marine organisms are already established in Asian countries. Squid cultured in
such facilities can be used as scientific experimental models, species for restocking,
J. Nabhitabhata and Y. Ikeda