294
E. A. G. Vidal and S. von Boletzky
Preferably, paralarvae are fed on a variety of live foods (Vidal et al. 2002a).
The prey types used with success as food for rearing L. vulgaris and D. opalescens paralarvae are Artemia nauplii, metanauplii and adults, decapod crab zoeae,
copepods, mysid shrimp, fish larvae and other zooplankton organisms (Fig. 16.7)
(Tables 16.3 and 16.4). Hatchlings of both L. vulgaris and D. opalescens perform
external predigestion and ingest only the flesh of their crustacean prey (Boletzky
1974b; Franco-Santos and Vidal 2014). Their beaks are denticulated (Boletzky
1971), colourless and show a conspicuous slit, features that seems to be an adaptation to ease the ingestion of predigested flesh (Franco-Santos and Vidal 2014).
One of the most demanding chores in rearing squid paralarvae is to provide food
in the necessary quantity, quality and reliability. Cultured feed organisms such as
Artemia, copepods, mysids and decapod crab zoeae (especially those of hermit
crabs that can be kept in culture for long-term production of larvae; Villanueva
1994) have been demonstrated to represent a good standard food for many cephalopod hatchlings, including loliginid squids, and are very important to warrant a
steady supply of food as natural zooplankton resources are unreliable.
Paralarvae can capture and ingest prey of a very wide size range including prey
much larger than their own size (Fig. 16.7; Hanlon 1990; Yang et al. 1986). However, as size at hatching shows high individual variability, the ability of paralarvae
to capture prey of different sizes and swimming capabilities also vary considerably
(Vidal et al. 2002a).
D. opalescens hatchlings have limited swimming ability and prey capture skills
(Chen et al. 1996; Preuss et al. 1997), and feed on relatively smaller prey, such as
Artemia nauplii, zoeae and copepods. Although some paralarvae are also able to
capture large prey, such as early juvenile mysids, it is critical to supply smaller and
‘easy to catch’ prey during the first 2 weeks after hatching (Tables 16.3 and 16.4).
Later, feeding a variety of prey of different sizes and types are important so as to
match the different sizes and hunting abilities of same-aged but heterogeneously developing squid. When paralarvae reach 40–50 days of age (6–10 mm mantle length,
ML) and start to swim in schools, they require large and more energetically rewarding prey types, such as adult mysids, large zoeae, shrimp mysis and fish larvae
(Yang et al. 1983a; Vidal et al. 2002a).
It is perhaps significant that feeding interactions are often observed between
same-aged but different sized paralarvae during the first month after hatching and
before formation of schools. As large paralarvae are better fit to capture larger prey,
which cannot be enclosed within the arms, other paralarvae (usually smaller) can
eventually attack and feed on the same prey item (E.A.G. Vidal, personal observation) (Fig. 16.8). There seems to be a preference for attacking large prey already
subdued by another paralarva instead of a free prey, even when prey are abundant.
This behaviour was briefly reported by Hurley (1976) and allows smaller hatchlings
to feed on prey that they could not subdue alone and that a large squid could not
possibly ingest fully. Whether this is a natural behaviour or is induced under rearing
conditions due to high stocking densities needs to be evaluated.
Indeed, the key mechanisms by which paralarvae select their prey persist as an
area of much needed research. Prey type and swimming pattern play an important
E. A. G. Vidal and S. von Boletzky
Preferably, paralarvae are fed on a variety of live foods (Vidal et al. 2002a).
The prey types used with success as food for rearing L. vulgaris and D. opalescens paralarvae are Artemia nauplii, metanauplii and adults, decapod crab zoeae,
copepods, mysid shrimp, fish larvae and other zooplankton organisms (Fig. 16.7)
(Tables 16.3 and 16.4). Hatchlings of both L. vulgaris and D. opalescens perform
external predigestion and ingest only the flesh of their crustacean prey (Boletzky
1974b; Franco-Santos and Vidal 2014). Their beaks are denticulated (Boletzky
1971), colourless and show a conspicuous slit, features that seems to be an adaptation to ease the ingestion of predigested flesh (Franco-Santos and Vidal 2014).
One of the most demanding chores in rearing squid paralarvae is to provide food
in the necessary quantity, quality and reliability. Cultured feed organisms such as
Artemia, copepods, mysids and decapod crab zoeae (especially those of hermit
crabs that can be kept in culture for long-term production of larvae; Villanueva
1994) have been demonstrated to represent a good standard food for many cephalopod hatchlings, including loliginid squids, and are very important to warrant a
steady supply of food as natural zooplankton resources are unreliable.
Paralarvae can capture and ingest prey of a very wide size range including prey
much larger than their own size (Fig. 16.7; Hanlon 1990; Yang et al. 1986). However, as size at hatching shows high individual variability, the ability of paralarvae
to capture prey of different sizes and swimming capabilities also vary considerably
(Vidal et al. 2002a).
D. opalescens hatchlings have limited swimming ability and prey capture skills
(Chen et al. 1996; Preuss et al. 1997), and feed on relatively smaller prey, such as
Artemia nauplii, zoeae and copepods. Although some paralarvae are also able to
capture large prey, such as early juvenile mysids, it is critical to supply smaller and
‘easy to catch’ prey during the first 2 weeks after hatching (Tables 16.3 and 16.4).
Later, feeding a variety of prey of different sizes and types are important so as to
match the different sizes and hunting abilities of same-aged but heterogeneously developing squid. When paralarvae reach 40–50 days of age (6–10 mm mantle length,
ML) and start to swim in schools, they require large and more energetically rewarding prey types, such as adult mysids, large zoeae, shrimp mysis and fish larvae
(Yang et al. 1983a; Vidal et al. 2002a).
It is perhaps significant that feeding interactions are often observed between
same-aged but different sized paralarvae during the first month after hatching and
before formation of schools. As large paralarvae are better fit to capture larger prey,
which cannot be enclosed within the arms, other paralarvae (usually smaller) can
eventually attack and feed on the same prey item (E.A.G. Vidal, personal observation) (Fig. 16.8). There seems to be a preference for attacking large prey already
subdued by another paralarva instead of a free prey, even when prey are abundant.
This behaviour was briefly reported by Hurley (1976) and allows smaller hatchlings
to feed on prey that they could not subdue alone and that a large squid could not
possibly ingest fully. Whether this is a natural behaviour or is induced under rearing
conditions due to high stocking densities needs to be evaluated.
Indeed, the key mechanisms by which paralarvae select their prey persist as an
area of much needed research. Prey type and swimming pattern play an important