83
5 Nutrition as a Key Factor for Cephalopod Aquaculture
5.5 Carbohydrates
Contrary to proteins and lipids, carbohydrate (CH) nutrition in the common octopus has barely been investigated. Considering their limited abundance compared to
other macronutrients (normally under 1 % of total dry weight; Vlieg 1984; Kreuzer
1984), it is generally accepted that cephalopods do not have a specific requirement
for dietary CH (Lee 1994). While protein and amino acids are the primary energy
source for cephalopods, it has been reported that cephalopods including O� vulgaris
are able to rapidly catabolize dietary CH to account for energy demands in explosive activities such as prey capture and fleeing from predators (Morillo-Velarde
et al. 2011). Therefore, CH may significantly contribute to fuelling metabolism in
O� vulgaris under starvation conditions and, consequently, adequate CH inclusion
of diets for octopus culture should not be underestimated. The source of CH utilized
in diet formulation also needs to be considered. For instance, while glucose was
easily digested by O� vulgaris (O’Dor et al. 1984), a recent study has revealed that
other sugar types such as starch present in freeze-dried pea may exhibit extremely
low digestibility (Morillo-Velarde et al. 2012).
On the other hand, the existence of a CH metabolism has been suggested by
Sykes et al. (2009a), due to different temperatures of specific geographical locations that may influence the egg nutritional content and metabolism in S� officinalis. The sepia egg yolk is composed by a water-soluble glyco-lipoprotein (Ito et al.
1962; Blanchier 1981). This glyco-lipoprotein has 20 % lipids (with 65 % phospholipid and minor or no cholesterol contents) and 12.6 % of CHs (Ito and Fujii 1962).
In fact, cuttlefish eggs from Faro (Portugal) have more CHs than lipids (Sykes et al.
2012). Bouchaud (1991) studied the energetic expenditure of S� officinalis during
embryonic development and found that eggs with more than 0.075 g displayed a
similar amount of energy (1,600 J), which led to a theory on the use of yolk for
growth and catabolic purposes that is inversely correlated with temperature (e.g.
higher temperature implies higher catabolism). In addition, higher temperatures
will imply higher oxygen uptake by the embryo (Wolf et al. 1985), which is attained
by the increased water volumes of eggs (Sykes et al. 2009a).
5.6 Minerals
The elemental requirements of O� vulgaris, as for cephalopods in general, are poorly
understood. Nevertheless, it is accepted that octopuses, as carnivorous species, meet
the majority of their elemental requirements from the diet, although direct uptake
from the seawater has also been shown to occur through an ion balance mechanism
regulated by the digestive gland appendages (Wells and Wells 1989). A literature
review on the element concentrations in a series of tissues from cephalopods was
reported by Napoleão et al. (2005a). While specific (quantitative) requirements
for both essential and nonessential elements have not yet been determined, some
5 Nutrition as a Key Factor for Cephalopod Aquaculture
5.5 Carbohydrates
Contrary to proteins and lipids, carbohydrate (CH) nutrition in the common octopus has barely been investigated. Considering their limited abundance compared to
other macronutrients (normally under 1 % of total dry weight; Vlieg 1984; Kreuzer
1984), it is generally accepted that cephalopods do not have a specific requirement
for dietary CH (Lee 1994). While protein and amino acids are the primary energy
source for cephalopods, it has been reported that cephalopods including O� vulgaris
are able to rapidly catabolize dietary CH to account for energy demands in explosive activities such as prey capture and fleeing from predators (Morillo-Velarde
et al. 2011). Therefore, CH may significantly contribute to fuelling metabolism in
O� vulgaris under starvation conditions and, consequently, adequate CH inclusion
of diets for octopus culture should not be underestimated. The source of CH utilized
in diet formulation also needs to be considered. For instance, while glucose was
easily digested by O� vulgaris (O’Dor et al. 1984), a recent study has revealed that
other sugar types such as starch present in freeze-dried pea may exhibit extremely
low digestibility (Morillo-Velarde et al. 2012).
On the other hand, the existence of a CH metabolism has been suggested by
Sykes et al. (2009a), due to different temperatures of specific geographical locations that may influence the egg nutritional content and metabolism in S� officinalis. The sepia egg yolk is composed by a water-soluble glyco-lipoprotein (Ito et al.
1962; Blanchier 1981). This glyco-lipoprotein has 20 % lipids (with 65 % phospholipid and minor or no cholesterol contents) and 12.6 % of CHs (Ito and Fujii 1962).
In fact, cuttlefish eggs from Faro (Portugal) have more CHs than lipids (Sykes et al.
2012). Bouchaud (1991) studied the energetic expenditure of S� officinalis during
embryonic development and found that eggs with more than 0.075 g displayed a
similar amount of energy (1,600 J), which led to a theory on the use of yolk for
growth and catabolic purposes that is inversely correlated with temperature (e.g.
higher temperature implies higher catabolism). In addition, higher temperatures
will imply higher oxygen uptake by the embryo (Wolf et al. 1985), which is attained
by the increased water volumes of eggs (Sykes et al. 2009a).
5.6 Minerals
The elemental requirements of O� vulgaris, as for cephalopods in general, are poorly
understood. Nevertheless, it is accepted that octopuses, as carnivorous species, meet
the majority of their elemental requirements from the diet, although direct uptake
from the seawater has also been shown to occur through an ion balance mechanism
regulated by the digestive gland appendages (Wells and Wells 1989). A literature
review on the element concentrations in a series of tissues from cephalopods was
reported by Napoleão et al. (2005a). While specific (quantitative) requirements
for both essential and nonessential elements have not yet been determined, some