444
J. Iglesias and L. Fuentes
white (or clear) bottom can be used in order to improve observation of the paralarvae. Temperature should be kept at 20–22 ºC and salinity 32–35 psu. Tangential surface water input and drainage consisting of a central cylindrical pipe with 250 µm
mesh are suggested. Another option is to use stagnant water during the day and open
the flow during the night with a 500-µm outlet mesh in order to keep a more homogeneous enriched Artemia. Surface cleaners and moderate central aeration are recommended. Surface light intensity should be 500–700 Lx for 24 h photoperiod when
using black wall and black bottom tanks, whereas light intensity can be 60–250 Lx
for a 14 h:10 h (L:D) photoperiod when a clear bottom tank is used. A concentration
of 1 × 10
6
cells mL
−1
of Nannochloropsis sp. should be used in the culture medium
(green-water system), and paralarvae concentration should be 10 individuals L
−1
.
Paralarval prey should consist of 24 h Artemia (0.5 Artemia mL
−1
) enriched with I�
galbana at a concentration of 0.75 × 10
6
cells mL
−1
for the first 15 days, followed
by larger Artemia (1.5–2 mm TL) cultured for 4–5 days with I� galbana and further
enriched with Nannochloropsis sp., at a concentration of 1 × 10
7
cells mL
−1
, keeping
a prey concentration of 0.3 Artemia mL
−1
. When zoeae of spider crab are used in
co-feeding with Artemia, they should be added at a concentration of 0.05–0.1 individuals mL
−1
, at least 3–4 days per week but preferably every day.
For comparative purposes, total length and dry weight of 20 paralarvae should
be recorded at the beginning of experiments and periodically (fortnightly is recommended) in each rearing trial.
23.7 Settlement Process
Around 65–75 days after hatching (at 20 ºC), when paralarvae have between 17 and
20 suckers per arm, they change their pelagic behaviour to a benthic life. At this
stage, paralarvae start crawling on the walls and bottom of the tank, moving by attaching their arms to the substrate. This period, which lasts for 2 weeks before they
fully adapt to benthic stage, is known as settlement.
During this phase, it is necessary to change feeding and habitat conditions. Artemia concentration should be gradually reduced while the benthic juveniles are
increasingly fed with mussel, crab and sea urchin muscle and gonad (Iglesias et al.
2004) and/or frozen mysidaceans (Carrasco et al. 2005). In both cases, the authors
placed small-angle or T-shaped PVC pieces on the bottom of the tanks as shelters
and the bottom substrate was modified by the inclusion of pebbles (Fig. 23.6).
23.8 Conclusions
Reproduction in captivity has proved feasible on an experimental scale, but the high
mortality observed during the paralarval and settlement stages are still the main
constraints to the industrial cultivation of the common octopus.
J. Iglesias and L. Fuentes
white (or clear) bottom can be used in order to improve observation of the paralarvae. Temperature should be kept at 20–22 ºC and salinity 32–35 psu. Tangential surface water input and drainage consisting of a central cylindrical pipe with 250 µm
mesh are suggested. Another option is to use stagnant water during the day and open
the flow during the night with a 500-µm outlet mesh in order to keep a more homogeneous enriched Artemia. Surface cleaners and moderate central aeration are recommended. Surface light intensity should be 500–700 Lx for 24 h photoperiod when
using black wall and black bottom tanks, whereas light intensity can be 60–250 Lx
for a 14 h:10 h (L:D) photoperiod when a clear bottom tank is used. A concentration
of 1 × 10
6
cells mL
−1
of Nannochloropsis sp. should be used in the culture medium
(green-water system), and paralarvae concentration should be 10 individuals L
−1
.
Paralarval prey should consist of 24 h Artemia (0.5 Artemia mL
−1
) enriched with I�
galbana at a concentration of 0.75 × 10
6
cells mL
−1
for the first 15 days, followed
by larger Artemia (1.5–2 mm TL) cultured for 4–5 days with I� galbana and further
enriched with Nannochloropsis sp., at a concentration of 1 × 10
7
cells mL
−1
, keeping
a prey concentration of 0.3 Artemia mL
−1
. When zoeae of spider crab are used in
co-feeding with Artemia, they should be added at a concentration of 0.05–0.1 individuals mL
−1
, at least 3–4 days per week but preferably every day.
For comparative purposes, total length and dry weight of 20 paralarvae should
be recorded at the beginning of experiments and periodically (fortnightly is recommended) in each rearing trial.
23.7 Settlement Process
Around 65–75 days after hatching (at 20 ºC), when paralarvae have between 17 and
20 suckers per arm, they change their pelagic behaviour to a benthic life. At this
stage, paralarvae start crawling on the walls and bottom of the tank, moving by attaching their arms to the substrate. This period, which lasts for 2 weeks before they
fully adapt to benthic stage, is known as settlement.
During this phase, it is necessary to change feeding and habitat conditions. Artemia concentration should be gradually reduced while the benthic juveniles are
increasingly fed with mussel, crab and sea urchin muscle and gonad (Iglesias et al.
2004) and/or frozen mysidaceans (Carrasco et al. 2005). In both cases, the authors
placed small-angle or T-shaped PVC pieces on the bottom of the tanks as shelters
and the bottom substrate was modified by the inclusion of pebbles (Fig. 23.6).
23.8 Conclusions
Reproduction in captivity has proved feasible on an experimental scale, but the high
mortality observed during the paralarval and settlement stages are still the main
constraints to the industrial cultivation of the common octopus.