455
24 Octopus vulgaris: Ongrowing
levels at the outlet. Consequently, the oxygen available per litre of water for cultivated octopus falls as the temperature increases, so that the flow must be increased.
Figure 24.1 shows the flows, expressed as L h
−1
and per kg of octopus, as a function
of the mean weight of the latter and at different temperatures. As can be seen, and
based on the above, the water flow must be increased dramatically as the temperature rises, especially at 21–24 °C.
24.3.2 Generation of Solid Wastes and Nitrogenated Products
In general, natural diets generate a large amount of wastes, and this is particularly true
in the case of cephalopods. The common octopus uses 77 % of the bogue supplied,
leaving as solid waste the head, spine and tail, while it uses 50 % of crab when given
as food, leaving the carapace (Mazón et al. 2007). These authors also estimated that
of the nitrogen intake, 33–37 % is incorporated into the body (growth), and 1–2 % is
eliminated in particulate form (faeces) and 62–65 % in dissolved form (excretion). The
latter is the most pernicious in land-based ongrowing systems, particularly recirculating water supply systems, since the nitrogenated products may become a limiting factor. In cephalopods, the major final product of protein catabolism is ammonium (Potts
1965; Boucher-Rodoni and Mangold 1985), while urea represents a low percentage
(Hoeger et al. 1987), which is rapidly hydrolyzed to ammonium and carbon dioxide. The absolute excretion rate of ammonium in octopus depends on the weight and
amount of protein ingested and can be expressed by an equation (García García et al.
2011), while, in relative terms (related with BW), it has a value of 84 mg TAN kg
−1
BW day
−1
when the octopus is not fed and 265 mg TAN kg
−1
BW day
−1
when protein
ingestion is 9 g day
−1
. The excretion rate as a function of quantity of food supplied
when the level of protein is not limiting varies linearly as a function of BW from 10 to
57 g TAN kg
−1
feed dry matter day
−1
when protein ingestion is 9 g day
−1
.
24.3.3 Transport
The need to use live cephalopods has led to the development of a variety of transportation systems. Adult octopuses can tolerate quite extreme transport conditions,
as long as the water temperature does not exceed 20 °C (Aguado-Giménez et al.
2001) and the level of dissolved oxygen is suitable. In Galicia, fishermen transport
octopus to the ongrowing cages in tubes wrapped in nets, thus avoiding aggressive
behaviour among the animals. At the experimental level, simulating transport for
24 h, Fuentes et al. (2005) obtained mortality rates of less than 5 % under extreme
density and temperature conditions (165 kg m
−3
, 19.5 °C). Estefanell (2012) used
500-L tanks and an oxygenation system to maintain the levels of dissolved oxygen
at 10–12 mg L
−1
; in this way, they transported adult octopuses (1 kg) at a maximum
density of 40 kg m
−3
for 60–70 min.
24 Octopus vulgaris: Ongrowing
levels at the outlet. Consequently, the oxygen available per litre of water for cultivated octopus falls as the temperature increases, so that the flow must be increased.
Figure 24.1 shows the flows, expressed as L h
−1
and per kg of octopus, as a function
of the mean weight of the latter and at different temperatures. As can be seen, and
based on the above, the water flow must be increased dramatically as the temperature rises, especially at 21–24 °C.
24.3.2 Generation of Solid Wastes and Nitrogenated Products
In general, natural diets generate a large amount of wastes, and this is particularly true
in the case of cephalopods. The common octopus uses 77 % of the bogue supplied,
leaving as solid waste the head, spine and tail, while it uses 50 % of crab when given
as food, leaving the carapace (Mazón et al. 2007). These authors also estimated that
of the nitrogen intake, 33–37 % is incorporated into the body (growth), and 1–2 % is
eliminated in particulate form (faeces) and 62–65 % in dissolved form (excretion). The
latter is the most pernicious in land-based ongrowing systems, particularly recirculating water supply systems, since the nitrogenated products may become a limiting factor. In cephalopods, the major final product of protein catabolism is ammonium (Potts
1965; Boucher-Rodoni and Mangold 1985), while urea represents a low percentage
(Hoeger et al. 1987), which is rapidly hydrolyzed to ammonium and carbon dioxide. The absolute excretion rate of ammonium in octopus depends on the weight and
amount of protein ingested and can be expressed by an equation (García García et al.
2011), while, in relative terms (related with BW), it has a value of 84 mg TAN kg
−1
BW day
−1
when the octopus is not fed and 265 mg TAN kg
−1
BW day
−1
when protein
ingestion is 9 g day
−1
. The excretion rate as a function of quantity of food supplied
when the level of protein is not limiting varies linearly as a function of BW from 10 to
57 g TAN kg
−1
feed dry matter day
−1
when protein ingestion is 9 g day
−1
.
24.3.3 Transport
The need to use live cephalopods has led to the development of a variety of transportation systems. Adult octopuses can tolerate quite extreme transport conditions,
as long as the water temperature does not exceed 20 °C (Aguado-Giménez et al.
2001) and the level of dissolved oxygen is suitable. In Galicia, fishermen transport
octopus to the ongrowing cages in tubes wrapped in nets, thus avoiding aggressive
behaviour among the animals. At the experimental level, simulating transport for
24 h, Fuentes et al. (2005) obtained mortality rates of less than 5 % under extreme
density and temperature conditions (165 kg m
−3
, 19.5 °C). Estefanell (2012) used
500-L tanks and an oxygenation system to maintain the levels of dissolved oxygen
at 10–12 mg L
−1
; in this way, they transported adult octopuses (1 kg) at a maximum
density of 40 kg m
−3
for 60–70 min.