305
16 Loligo vulgaris and Doryteuthis opalescens
16.7.1 Tank and Sea Cage Conditions
Since fin abrasion is one of the most important dangers in loliginid squid culture
(Boletzky 1979; Hanlon et al. 1979), any tank or sea cage would have to be designed to provide sufficient tank space to minimize contact of individuals with the
tank or cage walls. Large circular tanks or long-oval raceway tanks have proven
to be effective to reduce fin damage during the ongrowing of D. opalescens (Yang
et al. 1983a, 1986), although they have high costs of maintenance. Probably sea
cages would have to be equipped with light sources allowing the captive animals to
stay clear of the surrounding mesh walls during darkness.
16.7.2 Density
Density as such (number of individuals per volume of tank water) is not a meaningful criterion as soon as young individuals start schooling. The question then is more
about how many organized groups of individuals can be maintained in one tank or
sea cage. The constant risk of cannibalism draws attention to the likely necessity of
a rather strict separation of size classes in different holding facilities.
16.7.3 Food
Live fish and shrimps (Tables 16.3 and 16.4) or dead food items offered (e.g. pieces
of fish or entirely artificial preparations) are seized and eaten by hungry squids, and
any combination of these feeding regimes may be used to maintain a high degree
of appetence (for food other than conspecifics!). What can be considered a hungry
squid may be assessed by the actual feeding behaviour.
Fields (1965, p. 22) already described feeding behaviour in the aquarium: ‘On
one occasion, about 200 shrimp ( Spirontocaris sp.) were added to a tank (about
12 by 4 by 2 feet deep) in which about 40 D. opalescens had been shuttling back
and forth for 3 days. Some of the squid immediately showed excitement: clouds
of colour raced over their translucent mantles, the respiratory rate increased, the
animalʼs movements quickened and in each the sessile arms, hiding the tentacles,
formed a sharp cone pointing directly at a swimming shrimp. A squid would make
two or three short darts toward and from the prey, coming closer with each approach
until, on the last, the tentacles shot out to seize the shrimp and the arms opened for
its reception’.
Yang et al. (1986) offered a diet consisting of mysids, palaemonid shrimp and
estuarine fishes to D. opalescens juveniles and adults (Table 16.4), obtaining mean
daily group feeding rates of 14.9 and 18.0 % body ww.
16 Loligo vulgaris and Doryteuthis opalescens
16.7.1 Tank and Sea Cage Conditions
Since fin abrasion is one of the most important dangers in loliginid squid culture
(Boletzky 1979; Hanlon et al. 1979), any tank or sea cage would have to be designed to provide sufficient tank space to minimize contact of individuals with the
tank or cage walls. Large circular tanks or long-oval raceway tanks have proven
to be effective to reduce fin damage during the ongrowing of D. opalescens (Yang
et al. 1983a, 1986), although they have high costs of maintenance. Probably sea
cages would have to be equipped with light sources allowing the captive animals to
stay clear of the surrounding mesh walls during darkness.
16.7.2 Density
Density as such (number of individuals per volume of tank water) is not a meaningful criterion as soon as young individuals start schooling. The question then is more
about how many organized groups of individuals can be maintained in one tank or
sea cage. The constant risk of cannibalism draws attention to the likely necessity of
a rather strict separation of size classes in different holding facilities.
16.7.3 Food
Live fish and shrimps (Tables 16.3 and 16.4) or dead food items offered (e.g. pieces
of fish or entirely artificial preparations) are seized and eaten by hungry squids, and
any combination of these feeding regimes may be used to maintain a high degree
of appetence (for food other than conspecifics!). What can be considered a hungry
squid may be assessed by the actual feeding behaviour.
Fields (1965, p. 22) already described feeding behaviour in the aquarium: ‘On
one occasion, about 200 shrimp ( Spirontocaris sp.) were added to a tank (about
12 by 4 by 2 feet deep) in which about 40 D. opalescens had been shuttling back
and forth for 3 days. Some of the squid immediately showed excitement: clouds
of colour raced over their translucent mantles, the respiratory rate increased, the
animalʼs movements quickened and in each the sessile arms, hiding the tentacles,
formed a sharp cone pointing directly at a swimming shrimp. A squid would make
two or three short darts toward and from the prey, coming closer with each approach
until, on the last, the tentacles shot out to seize the shrimp and the arms opened for
its reception’.
Yang et al. (1986) offered a diet consisting of mysids, palaemonid shrimp and
estuarine fishes to D. opalescens juveniles and adults (Table 16.4), obtaining mean
daily group feeding rates of 14.9 and 18.0 % body ww.