456
F. J. Sánchez et al.
24.3.4 Octopus Ongrowing as a Function of Sex,
Initial weight and Stocking Density
First commercial attempts to rear O� vulgaris used circulating water tanks and floating cages in the late 1990s. These experiments were designed to determine the optimal rearing conditions to reach a commercial size (2.5–3.5 kg). It was found that
males grow slightly more rapidly than females (Sánchez et al. 1998), although the
final weights of both sexes in ongrowing cages did not differ if they were cultivated
separately. Studies on growth, oxygen consumption and ammonia production carried
out excluding the period of gonadal maturation in females showed no significant differences between males and females (Aguado-Giménez and García García 2002; Cerezo Valverde and García García 2004; García García et al. 2011). Moreover, the best
performance in ongrowing trials was observed with no or low state of sexual maturation in females (Estefanell et al. 2012b, 2013). Indeed, maturing of females during the
rearing period has been a problem because from the moment egg laying occurs stop
eating and grow. In this sense, Chapela et al. (2006) suggest separation of sexes prior
to ongrowing process and prevent loss of commercial value. However, companies engaged in floating sea cages rearing octopus, mixed male and female in the same cage
for practical reasons.
Another important factor to take into account is the initial weight of octopuses,
since in many markets animals weighing more than 2 kg reach a higher price. Indeed, one of the advantages of cephalopods is the rate at which they grow: starting
ongrowing with individuals of 330 g, they can reach market size (> 2 kg) in 4 months
(Iglesias et al. 2000). However, in the current situation, the companies prefer to start
ongrowing with octopuses of 1 kg because the survival and absolute growth are
higher and lower rearing time is necessary, thus obtaining a higher profit.
For the ongrowing of both juveniles and adults, the initial stocking density in tanks
and cages is of great importance since the growth rate is so high that the initial biomass can triplicate in a few weeks, generating problems related to oxygen consumption and detritus production and even the creation of hierarchies as a result of size
variations. This leads to stress and may end in cases of cannibalism and autophagy.
In experiments using juveniles cultivated at different initial densities (10 kg m
−3
and
20 kg m
−3
) in tanks, Iglesias et al. (2000) found no differences in growth between
the groups after 56 days but found that survival was greater in the lower density
group. Chapela et al. (2006) recommended using similar-sized octopuses in floating cages (eight animals at 14 kg m
−3
). The same authors used food of low value or
from by-catch, composed of fish, crustaceans and mussels. Under these conditions,
juveniles weighing 700–1,000 g reached a weight of 3 kg in 3 or 4 months, and it
was possible to have two or three ongrowing cycles per year, avoiding winter, when
growth is poorer. Working with the same cages, Iglesias et al. (2007) also recorded
higher weights in summer, while in experiments made in floating cages measuring
4 × 3 x 1 m, Rodríguez et al. (2006) used octopuses at different concentrations and at
different times of the year in northern Spain, finding the best results at initial concentrations of 10–12 kg m
−3
and temperatures of 15–21 °C in spring–summer. Domingues
et al. (2010) found no significant differences in growth to initial densities of 4, 8 and
15 kg m
−3
in tanks; nevertheless, mortality was significantly lower for the low density.
F. J. Sánchez et al.
24.3.4 Octopus Ongrowing as a Function of Sex,
Initial weight and Stocking Density
First commercial attempts to rear O� vulgaris used circulating water tanks and floating cages in the late 1990s. These experiments were designed to determine the optimal rearing conditions to reach a commercial size (2.5–3.5 kg). It was found that
males grow slightly more rapidly than females (Sánchez et al. 1998), although the
final weights of both sexes in ongrowing cages did not differ if they were cultivated
separately. Studies on growth, oxygen consumption and ammonia production carried
out excluding the period of gonadal maturation in females showed no significant differences between males and females (Aguado-Giménez and García García 2002; Cerezo Valverde and García García 2004; García García et al. 2011). Moreover, the best
performance in ongrowing trials was observed with no or low state of sexual maturation in females (Estefanell et al. 2012b, 2013). Indeed, maturing of females during the
rearing period has been a problem because from the moment egg laying occurs stop
eating and grow. In this sense, Chapela et al. (2006) suggest separation of sexes prior
to ongrowing process and prevent loss of commercial value. However, companies engaged in floating sea cages rearing octopus, mixed male and female in the same cage
for practical reasons.
Another important factor to take into account is the initial weight of octopuses,
since in many markets animals weighing more than 2 kg reach a higher price. Indeed, one of the advantages of cephalopods is the rate at which they grow: starting
ongrowing with individuals of 330 g, they can reach market size (> 2 kg) in 4 months
(Iglesias et al. 2000). However, in the current situation, the companies prefer to start
ongrowing with octopuses of 1 kg because the survival and absolute growth are
higher and lower rearing time is necessary, thus obtaining a higher profit.
For the ongrowing of both juveniles and adults, the initial stocking density in tanks
and cages is of great importance since the growth rate is so high that the initial biomass can triplicate in a few weeks, generating problems related to oxygen consumption and detritus production and even the creation of hierarchies as a result of size
variations. This leads to stress and may end in cases of cannibalism and autophagy.
In experiments using juveniles cultivated at different initial densities (10 kg m
−3
and
20 kg m
−3
) in tanks, Iglesias et al. (2000) found no differences in growth between
the groups after 56 days but found that survival was greater in the lower density
group. Chapela et al. (2006) recommended using similar-sized octopuses in floating cages (eight animals at 14 kg m
−3
). The same authors used food of low value or
from by-catch, composed of fish, crustaceans and mussels. Under these conditions,
juveniles weighing 700–1,000 g reached a weight of 3 kg in 3 or 4 months, and it
was possible to have two or three ongrowing cycles per year, avoiding winter, when
growth is poorer. Working with the same cages, Iglesias et al. (2007) also recorded
higher weights in summer, while in experiments made in floating cages measuring
4 × 3 x 1 m, Rodríguez et al. (2006) used octopuses at different concentrations and at
different times of the year in northern Spain, finding the best results at initial concentrations of 10–12 kg m
−3
and temperatures of 15–21 °C in spring–summer. Domingues
et al. (2010) found no significant differences in growth to initial densities of 4, 8 and
15 kg m
−3
in tanks; nevertheless, mortality was significantly lower for the low density.