419
22 Octopus minor
22.3.3 Spawning and Egg Handing
Octopus shelters are usually checked daily and confirmed whether or not eggs appear in the internal walls. As happens in other species, food intake of broodstock
decreases sharply once they start to spawn. Females show the behaviour of protecting the egg masses. To avoid other individuals disturbing the spawning female,
both ends of the shelter pipes are firmly sealed with a 0.85 mm-diameter fine mesh,
so that a female would be able to stay safely with her eggs. Most of the eggs are
attached one by one to the inner walls of the shelter. Each egg looks like a long
eggplant in shape, with a long diameter of 13–20 mm, a short diameter of 4–6 mm
and with a wet weight of 0.15–0.26 g. The number of spawned eggs per female
ranges from 9 to 125, depending on the weight among individuals. In general, the
spawning time lasts for 1 week per female. Once an individual starts to spawn, it
is able to stimulate the others to do the same. The entire spawning period can be
extended to at least 1 month, because more than 100 females can be used for the
same broodstock.
It is well known that during the spawning period, females hardly eat food in the
wild. But they can eat a small amount of food soon after being captured from the sea
and taken into the indoor culture conditions. Consequently, some fresh food such as
one to two half-shell clams, or crabs without claws, is still supplied to the shelters
every 3–5 days. Any leftover food must be retrieved the next morning, to prevent
the deterioration of the water quality. Meanwhile, seawater keeps flowing continuously. Under these conditions, most females protect their eggs until hatching.
The embryonic development of O� minor lasts for 72–89 days before hatching
under the conditions of a seawater temperature of 21–25 °C and a salinity of 28–
31 psu. At this temperature range, the process of embryonic development is divided
into 20 stages (Fig. 22.4) differentiated by characteristic changes, such as cleavage,
blastula formation, gastrula formation, organ rudiment formation as well as two embryo reverses (Qian et al. 2013). The first embryonic reversal takes place at stages
VI–VII on day 21 (Fig. 22.4), and embryos turn from the animal pole to the vegetal
pole. The second embryonic inversion happens at stage XIX on day 65 (Fig. 22.4).
Sporadically, more than two reverses were also observed. The mantle length and
total length of hatchlings range from 8.5 to 11.5 mm and from 25 to 31 mm, respectively. And after hatching, they already show benthic behaviour.
22.4 Hatchlings Rearing
New hatchlings are very sensitive to the environment and they can eject ink easily
in response to any external stimuli, which may trigger a major injury. To function
as a den, it is effective and feasible to place in advance some green macroalgae or
seaweed (e.g. Ulva pertusa, Zostera marina) in the breeding pools. In the case of
22 Octopus minor
22.3.3 Spawning and Egg Handing
Octopus shelters are usually checked daily and confirmed whether or not eggs appear in the internal walls. As happens in other species, food intake of broodstock
decreases sharply once they start to spawn. Females show the behaviour of protecting the egg masses. To avoid other individuals disturbing the spawning female,
both ends of the shelter pipes are firmly sealed with a 0.85 mm-diameter fine mesh,
so that a female would be able to stay safely with her eggs. Most of the eggs are
attached one by one to the inner walls of the shelter. Each egg looks like a long
eggplant in shape, with a long diameter of 13–20 mm, a short diameter of 4–6 mm
and with a wet weight of 0.15–0.26 g. The number of spawned eggs per female
ranges from 9 to 125, depending on the weight among individuals. In general, the
spawning time lasts for 1 week per female. Once an individual starts to spawn, it
is able to stimulate the others to do the same. The entire spawning period can be
extended to at least 1 month, because more than 100 females can be used for the
same broodstock.
It is well known that during the spawning period, females hardly eat food in the
wild. But they can eat a small amount of food soon after being captured from the sea
and taken into the indoor culture conditions. Consequently, some fresh food such as
one to two half-shell clams, or crabs without claws, is still supplied to the shelters
every 3–5 days. Any leftover food must be retrieved the next morning, to prevent
the deterioration of the water quality. Meanwhile, seawater keeps flowing continuously. Under these conditions, most females protect their eggs until hatching.
The embryonic development of O� minor lasts for 72–89 days before hatching
under the conditions of a seawater temperature of 21–25 °C and a salinity of 28–
31 psu. At this temperature range, the process of embryonic development is divided
into 20 stages (Fig. 22.4) differentiated by characteristic changes, such as cleavage,
blastula formation, gastrula formation, organ rudiment formation as well as two embryo reverses (Qian et al. 2013). The first embryonic reversal takes place at stages
VI–VII on day 21 (Fig. 22.4), and embryos turn from the animal pole to the vegetal
pole. The second embryonic inversion happens at stage XIX on day 65 (Fig. 22.4).
Sporadically, more than two reverses were also observed. The mantle length and
total length of hatchlings range from 8.5 to 11.5 mm and from 25 to 31 mm, respectively. And after hatching, they already show benthic behaviour.
22.4 Hatchlings Rearing
New hatchlings are very sensitive to the environment and they can eject ink easily
in response to any external stimuli, which may trigger a major injury. To function
as a den, it is effective and feasible to place in advance some green macroalgae or
seaweed (e.g. Ulva pertusa, Zostera marina) in the breeding pools. In the case of