322
length (Lee et al. 1994; Nabhitabhata 1978, 1996), and with BWs of approximately
0.04 g. Hatchlings in good health swim with their heads down and hover at a 45–60°
angle at approximately 75 % of the total water depth above the bottom of the tank.
They begin to feed immediately after hatching. Hatchlings are photopositive and
prefer low-intensity light (Nabhitabhata 1978; Nabhitabhata and Kbinrum 1981).
Hatchlings are dark brown in the light and are pale or transparent in dim light or
dark areas. The arms are still comparatively short, but they are strong enough to
catch prey that are equal to, or sometimes larger than, their own ML. When feeding
on small crustaceans, hatchlings seize prey using their arms and the prey are bitten
at the posterior part of the carapace. The tail parts of the prey are eaten first, and then
the flesh is gradually consumed. The hard structures of the prey are left uneaten.
Water Quality and System Requirements
The planktonic habit of hatchlings requires a directed current that allows them to
hover in the water column. Aeration has to be managed to generate a directional
flow in the tanks. Adjusting the current velocity to an optimum velocity can reduce
stress and the energy consumption required for countercurrent swimming. The optimum current velocity can be observed from the angle of hovering. The hovering
angle should be 45–60° to the tank bottom at all times. A simple air-lift system is
used to generate the appropriate horizontal flow in the cylindrical tank. In a circular
tank that is 2–3 m in diameter with a water depth of 0.6 m, such a system can be
constructed from a PVC pipe that is 50 mm in diameter and 800 mm in length and
that has been cut longitudinally in half (for details of a similar system on a smaller
scale, see Chap. 15 ‘Euprymna hyllebergi’; Fig. 15.3). Each half is drilled at one
end where an air pipe and air stone are inserted into the interior face. Both prepared
half-pipes are placed facing the same direction at a 45° angle with the air stone at
the bottom of the tank. The number of these flow-generating pipe sets used in one
tank depends on the size and shape of the tank. At least two sets are required in
each circular tank and at least four sets are needed in each rectangular tank, one set
at each corner. The current velocity can be adjusted by adjusting the aeration rate.
The maintenance of water quality and tank management in the nursing phase
may need to be adjusted from those of the egg-nursing phase. Hatchlings can tolerate a range of salinity from 20 to 40 psu for at least 24 h. The salinity required for
more than 50 % survival is 23–36 psu and the pH required for more than 50 % survival is 6.3–8.4 (Nabhitabhata et al. 1991a, 1992a, 2001c; Nabhitabhata and Kbinrum 1984). S� lessoniana hatchlings can tolerate ammonia concentrations (NH 4 -N)
up to 0.06 mg·L
−1
, nitrite (NO 2 -N) up to 0.08 mg·L
−1
, and phosphate (PO 4 -P) up to
6.0 mg·L
−1
(Chindamaikul et al. 2001; Chainak et al. 2003). The routine management of nursing tanks follows directly from the egg-nursing phase.
In larger tanks, the water level in the nursery tanks is adjusted to accommodate the number and size of live feed organisms. An appropriate level of the feed
and cephalopod biomass in the tank reduces excess food-hunting activity. The
initial water depth is 500 mm at hatching and the density of hatchlings is 5–10
J. Nabhitabhata and Y. Ikeda
length (Lee et al. 1994; Nabhitabhata 1978, 1996), and with BWs of approximately
0.04 g. Hatchlings in good health swim with their heads down and hover at a 45–60°
angle at approximately 75 % of the total water depth above the bottom of the tank.
They begin to feed immediately after hatching. Hatchlings are photopositive and
prefer low-intensity light (Nabhitabhata 1978; Nabhitabhata and Kbinrum 1981).
Hatchlings are dark brown in the light and are pale or transparent in dim light or
dark areas. The arms are still comparatively short, but they are strong enough to
catch prey that are equal to, or sometimes larger than, their own ML. When feeding
on small crustaceans, hatchlings seize prey using their arms and the prey are bitten
at the posterior part of the carapace. The tail parts of the prey are eaten first, and then
the flesh is gradually consumed. The hard structures of the prey are left uneaten.
Water Quality and System Requirements
The planktonic habit of hatchlings requires a directed current that allows them to
hover in the water column. Aeration has to be managed to generate a directional
flow in the tanks. Adjusting the current velocity to an optimum velocity can reduce
stress and the energy consumption required for countercurrent swimming. The optimum current velocity can be observed from the angle of hovering. The hovering
angle should be 45–60° to the tank bottom at all times. A simple air-lift system is
used to generate the appropriate horizontal flow in the cylindrical tank. In a circular
tank that is 2–3 m in diameter with a water depth of 0.6 m, such a system can be
constructed from a PVC pipe that is 50 mm in diameter and 800 mm in length and
that has been cut longitudinally in half (for details of a similar system on a smaller
scale, see Chap. 15 ‘Euprymna hyllebergi’; Fig. 15.3). Each half is drilled at one
end where an air pipe and air stone are inserted into the interior face. Both prepared
half-pipes are placed facing the same direction at a 45° angle with the air stone at
the bottom of the tank. The number of these flow-generating pipe sets used in one
tank depends on the size and shape of the tank. At least two sets are required in
each circular tank and at least four sets are needed in each rectangular tank, one set
at each corner. The current velocity can be adjusted by adjusting the aeration rate.
The maintenance of water quality and tank management in the nursing phase
may need to be adjusted from those of the egg-nursing phase. Hatchlings can tolerate a range of salinity from 20 to 40 psu for at least 24 h. The salinity required for
more than 50 % survival is 23–36 psu and the pH required for more than 50 % survival is 6.3–8.4 (Nabhitabhata et al. 1991a, 1992a, 2001c; Nabhitabhata and Kbinrum 1984). S� lessoniana hatchlings can tolerate ammonia concentrations (NH 4 -N)
up to 0.06 mg·L
−1
, nitrite (NO 2 -N) up to 0.08 mg·L
−1
, and phosphate (PO 4 -P) up to
6.0 mg·L
−1
(Chindamaikul et al. 2001; Chainak et al. 2003). The routine management of nursing tanks follows directly from the egg-nursing phase.
In larger tanks, the water level in the nursery tanks is adjusted to accommodate the number and size of live feed organisms. An appropriate level of the feed
and cephalopod biomass in the tank reduces excess food-hunting activity. The
initial water depth is 500 mm at hatching and the density of hatchlings is 5–10
J. Nabhitabhata and Y. Ikeda