354
J. Nabhitabhata
then used for the nursing of the young. The nursing tank has dark-blue walls and
is filled with filtered sea water to a water depth of 150 mm. In order to generate
and direct an artificial current, the tank is equipped with air stones attached to two
pieces of longitudinal PVC pipes (25 mm diameter, 400 mm length). Tanks are
cleaned by siphoning and about 80 % of the volume is replaced daily. The management method is similar to that for the previous phase and is also used for Euprymna
hyllebergi (see also Chap. 15, Fig. 15.3; Nabhitabhata et al. 2005; Promboon et al.
2011). Temperature changes are avoided using a water bath outside the rearing tank.
The average temperature should be maintained at approximately 30°C, a pH of 8
and salinity of 30 psu. (Promboon et al. 2011)
Amphioctopus aegina has planktonic hatchlings, and the pelagic phase lasts for
around 20–25 days at 30°C, before they subsequently complete their settling stage
about 1 week later, at day 30. From day 15 after hatching, the early settlers temporarily attach themselves to the tank wall and gradually increase their period of
attachment and their proximity of attachment to the tank bottom, their final habitat.
During the transitional settlement period, the depth of the attachment is gradually
increased by approximately 50 mm day
−1
. During this period, the young still attack
their prey in the water column but swim down to eat them at the tank bottom.
The general feeding schedule is to feed hatchlings planktonic food when they
are pelagic and column feeders, and provide them with benthic food after the settling stage, when they become benthic feeders. Hatchlings are fed twice daily with
live prawn zoea, Macrobrachium sintangense (available from commercial hatcheries) of 1–2 mm total length for 30 days after hatching. Live amphipods, Unciolella
sp., wild palaemonid shrimps, Exopalaemon styliferus and dwarf gobies, Redigobius
tambujon, collected from the wild, are used to feed the octopus young from their
transitional stage to their early post-settlement, days 25–50 (Fig. 18.4). Feeding has
to be ad libitum to generate a similar growth rate, hence there being less difference in
size or individual production, and to avoid subsequent cannibalism. Cannibalism has
occasionally been observed when size difference is more than 50 %, from hatching
to about 70 days.
The initial stocking density for hatchlings is one individual per litre at 150 mm
water depth. Such a depth is required to aggregate the food organisms and reduce excessive activity of the octopus. Water depth is gradually increased by about 50 mm
every day to attain a final depth of 300 mm at 30 days. The increasing water volume
corresponds to the increasing size of the octopus. Survival rate in this nursing phase
is only about 10 % because the live food might be not enough due to interruptions
to the daily supply. The requirement for live prawns at an exact life stage (zoea),
although commercially produced, makes daily and consistent supply difficult.
18.5.2 Growth
Marbled octopus hatchlings grow from 2.7 mm average ML and 0.003 g mean wet
weight (WW) at hatching to 6.3 mm ML and 0.068 g WW at the settling stage
(30 days after hatching). The daily growth rate in terms of instantaneous relative
J. Nabhitabhata
then used for the nursing of the young. The nursing tank has dark-blue walls and
is filled with filtered sea water to a water depth of 150 mm. In order to generate
and direct an artificial current, the tank is equipped with air stones attached to two
pieces of longitudinal PVC pipes (25 mm diameter, 400 mm length). Tanks are
cleaned by siphoning and about 80 % of the volume is replaced daily. The management method is similar to that for the previous phase and is also used for Euprymna
hyllebergi (see also Chap. 15, Fig. 15.3; Nabhitabhata et al. 2005; Promboon et al.
2011). Temperature changes are avoided using a water bath outside the rearing tank.
The average temperature should be maintained at approximately 30°C, a pH of 8
and salinity of 30 psu. (Promboon et al. 2011)
Amphioctopus aegina has planktonic hatchlings, and the pelagic phase lasts for
around 20–25 days at 30°C, before they subsequently complete their settling stage
about 1 week later, at day 30. From day 15 after hatching, the early settlers temporarily attach themselves to the tank wall and gradually increase their period of
attachment and their proximity of attachment to the tank bottom, their final habitat.
During the transitional settlement period, the depth of the attachment is gradually
increased by approximately 50 mm day
−1
. During this period, the young still attack
their prey in the water column but swim down to eat them at the tank bottom.
The general feeding schedule is to feed hatchlings planktonic food when they
are pelagic and column feeders, and provide them with benthic food after the settling stage, when they become benthic feeders. Hatchlings are fed twice daily with
live prawn zoea, Macrobrachium sintangense (available from commercial hatcheries) of 1–2 mm total length for 30 days after hatching. Live amphipods, Unciolella
sp., wild palaemonid shrimps, Exopalaemon styliferus and dwarf gobies, Redigobius
tambujon, collected from the wild, are used to feed the octopus young from their
transitional stage to their early post-settlement, days 25–50 (Fig. 18.4). Feeding has
to be ad libitum to generate a similar growth rate, hence there being less difference in
size or individual production, and to avoid subsequent cannibalism. Cannibalism has
occasionally been observed when size difference is more than 50 %, from hatching
to about 70 days.
The initial stocking density for hatchlings is one individual per litre at 150 mm
water depth. Such a depth is required to aggregate the food organisms and reduce excessive activity of the octopus. Water depth is gradually increased by about 50 mm
every day to attain a final depth of 300 mm at 30 days. The increasing water volume
corresponds to the increasing size of the octopus. Survival rate in this nursing phase
is only about 10 % because the live food might be not enough due to interruptions
to the daily supply. The requirement for live prawns at an exact life stage (zoea),
although commercially produced, makes daily and consistent supply difficult.
18.5.2 Growth
Marbled octopus hatchlings grow from 2.7 mm average ML and 0.003 g mean wet
weight (WW) at hatching to 6.3 mm ML and 0.068 g WW at the settling stage
(30 days after hatching). The daily growth rate in terms of instantaneous relative