335
17.3.2.3 Nursing of Young
Characters and Habit of Young
Compared to other loliginids, S� lessoniana hatchlings are much larger, with a 3.5–
6.4-mm ML (Lee et al. 1994). Hatching usually occurs at midnight and seldom occurs during daylight hours. After hatching, hatchlings (of ML 5–7 mm) swim gently
to maintain their position in the middle to upper water layer, keeping their mantle
upward and head obliquely downward (Segawa 1987). Hatchlings also assume an
upward or downward V-shaped position, while body colour is kept either all dark or
transparent. In the upward V-shaped position, the arms are divided into two rows,
like the letter ‘V’, while in the downward V-shaped position, all arms droop downward (Ikeda, unpublished observation). Hatchlings show positive phototaxis to a
beam of light at night (Segawa 1987). Because a similar behaviour is also observed
for hatchlings of Heterololigo bleekeri, another loliginid squid (Ikeda et al. 2005),
this may be a shared characteristic of loliginids at hatching. This characteristic likely contributes to keeping hatchlings at the surface layer where they are most likely
to encounter prey organisms and/or avoid predators.
The young begin to form schools in which individuals are positioned parallel to
their neighbours, and schools are completely formed within 2 months of hatching
(Sugimoto and Ikeda 2012).
Water Quality and System Requirements
In closed water systems, nursing of the young proceeds in the 20- or 50-L cylindrical egg-nursing tanks at a temperature of about 23–24 °C (Ikeda et al. 2003, 2009a;
Lee et al. 1994, 1998a, b). Such small tanks are advantageous in that prey organisms
aggregate in them and they are convenient for aquaculturists to manage. In addition, less seawater is required for closed systems than for open systems and they are
therefore economical. A 120-L circular tank can also be used to rear juveniles and
the young in a closed system; this relatively large tank enables the observation of
squid behaviours that require space (e.g. schooling and social interaction).
Feeding
Various species of mysids can be successfully provided as prey, e.g. the brackish
water crustaceans Neomysis japonica (Choe and Ohshima 1961; Ohshima and Choe
1961; Choe (1966a, b), Siriella longipes (Segawa 1990), and Mysidopsis almyra
(Lee et al. 1994). Other potential live feed organisms include small-sized or freshwater fish fry, e.g. guppy, Poecilia reticulata, or medaka, Oryzias latipes (Lee et al.
1994; Ikeda et al. 2003, 2009a).
Juvenile squid older than 1 month of age can adapt to feeding on dead organisms
that are thrown by humans into the water column. At first, squid neglect the dead
17 Sepioteuthis lessoniana
17.3.2.3 Nursing of Young
Characters and Habit of Young
Compared to other loliginids, S� lessoniana hatchlings are much larger, with a 3.5–
6.4-mm ML (Lee et al. 1994). Hatching usually occurs at midnight and seldom occurs during daylight hours. After hatching, hatchlings (of ML 5–7 mm) swim gently
to maintain their position in the middle to upper water layer, keeping their mantle
upward and head obliquely downward (Segawa 1987). Hatchlings also assume an
upward or downward V-shaped position, while body colour is kept either all dark or
transparent. In the upward V-shaped position, the arms are divided into two rows,
like the letter ‘V’, while in the downward V-shaped position, all arms droop downward (Ikeda, unpublished observation). Hatchlings show positive phototaxis to a
beam of light at night (Segawa 1987). Because a similar behaviour is also observed
for hatchlings of Heterololigo bleekeri, another loliginid squid (Ikeda et al. 2005),
this may be a shared characteristic of loliginids at hatching. This characteristic likely contributes to keeping hatchlings at the surface layer where they are most likely
to encounter prey organisms and/or avoid predators.
The young begin to form schools in which individuals are positioned parallel to
their neighbours, and schools are completely formed within 2 months of hatching
(Sugimoto and Ikeda 2012).
Water Quality and System Requirements
In closed water systems, nursing of the young proceeds in the 20- or 50-L cylindrical egg-nursing tanks at a temperature of about 23–24 °C (Ikeda et al. 2003, 2009a;
Lee et al. 1994, 1998a, b). Such small tanks are advantageous in that prey organisms
aggregate in them and they are convenient for aquaculturists to manage. In addition, less seawater is required for closed systems than for open systems and they are
therefore economical. A 120-L circular tank can also be used to rear juveniles and
the young in a closed system; this relatively large tank enables the observation of
squid behaviours that require space (e.g. schooling and social interaction).
Feeding
Various species of mysids can be successfully provided as prey, e.g. the brackish
water crustaceans Neomysis japonica (Choe and Ohshima 1961; Ohshima and Choe
1961; Choe (1966a, b), Siriella longipes (Segawa 1990), and Mysidopsis almyra
(Lee et al. 1994). Other potential live feed organisms include small-sized or freshwater fish fry, e.g. guppy, Poecilia reticulata, or medaka, Oryzias latipes (Lee et al.
1994; Ikeda et al. 2003, 2009a).
Juvenile squid older than 1 month of age can adapt to feeding on dead organisms
that are thrown by humans into the water column. At first, squid neglect the dead
17 Sepioteuthis lessoniana