307
16 Loligo vulgaris and Doryteuthis opalescens
16.9 Conclusions
Considering loliginid squid hatchlings as miniature cephalopods that already have
adult-like sensory organs and effector systems (Budelmann 1996), including muscular suckers allowing them to seize and hold live prey (Schmidtberg 1997), but
also special structures such as tailored denticulated beaks (Boletzky 1971; FrancoSantos and Vidal 2014), the complex requirements of their culture are not really
surprising.
The production of high-quality and competent paralarvae is dependent on the
developmental history and environmental influences during embryogenesis. Research progress has been slow in identifying the factors that endorse the production
of functional and competent paralarvae with large internal yolk reserves for rearing. This is a precursory step to reduce mortality during the critical transition from
endogenous (yolk) to exogenous feeding (prey capture) that takes place during the
first 10 dah when the highest mortality rates are observed. In this context, many
open questions remain about how the known physical and chemical parameters
act via the physiological mechanisms to control biological performance (including
predatory behaviour, digestion, growth) during the different phases of the life cycle.
So far, survival rates thus are the most reliable indicators for ‘good’ culture systems. A reproducible high rate of survival and growth of paralarvae is necessary to
achieve successful culture. Tank circulation and turbulence have a direct impact
on paralarval survival by increasing the incidence of skin and fin damage caused
by the contact of the fragile paralarvae with tank walls. More attention should be
given to the rearing systems as improvements on survival rates of paralarvae have
been related to advances in water quality and the design of culture systems (Yang
et al. 1983a; Vidal et al. 2002a). Nevertheless, large numbers of loliginid paralarvae
can be reared in the laboratory with relatively good survival rates in recirculating
systems if live food items are provided.
Paralarvae require a variety of live prey of different sizes and types so as to
match the different sizes and hunting abilities of same-aged but heterogeneously
developing squid. This is still one of the main bottlenecks in culturing, and a steady
supply of live, fresh, cultured food organisms (copepods, crab zoeae, mysids) can
greatly contribute to excellent survival rates on experimental level. Paralarvae feeding behaviour is noticeably experience based (Chen et al. 1996).
While food availability is essential during rearing, food quality is more important for development and growth. When squid reach 40–50 days of age (6–10 mm
ML) they require higher daily food intake, large and more energetically rewarding
prey types and more swimming space as they start swimming in schools. If these
requirements are not met, a second peak in mortality is often observed. Elucidating
ontogenetic size-specific nutritional requirements of squid is essential to improve
feeding and should be ranked as a high-priority research area.
For highly active swimmers such as loliginid squids, which begin schooling at
an early juvenile stage, sufficient tank space to allow expression of normal swimming and feeding behaviour and to accommodate relatively large groups is a major
16 Loligo vulgaris and Doryteuthis opalescens
16.9 Conclusions
Considering loliginid squid hatchlings as miniature cephalopods that already have
adult-like sensory organs and effector systems (Budelmann 1996), including muscular suckers allowing them to seize and hold live prey (Schmidtberg 1997), but
also special structures such as tailored denticulated beaks (Boletzky 1971; FrancoSantos and Vidal 2014), the complex requirements of their culture are not really
surprising.
The production of high-quality and competent paralarvae is dependent on the
developmental history and environmental influences during embryogenesis. Research progress has been slow in identifying the factors that endorse the production
of functional and competent paralarvae with large internal yolk reserves for rearing. This is a precursory step to reduce mortality during the critical transition from
endogenous (yolk) to exogenous feeding (prey capture) that takes place during the
first 10 dah when the highest mortality rates are observed. In this context, many
open questions remain about how the known physical and chemical parameters
act via the physiological mechanisms to control biological performance (including
predatory behaviour, digestion, growth) during the different phases of the life cycle.
So far, survival rates thus are the most reliable indicators for ‘good’ culture systems. A reproducible high rate of survival and growth of paralarvae is necessary to
achieve successful culture. Tank circulation and turbulence have a direct impact
on paralarval survival by increasing the incidence of skin and fin damage caused
by the contact of the fragile paralarvae with tank walls. More attention should be
given to the rearing systems as improvements on survival rates of paralarvae have
been related to advances in water quality and the design of culture systems (Yang
et al. 1983a; Vidal et al. 2002a). Nevertheless, large numbers of loliginid paralarvae
can be reared in the laboratory with relatively good survival rates in recirculating
systems if live food items are provided.
Paralarvae require a variety of live prey of different sizes and types so as to
match the different sizes and hunting abilities of same-aged but heterogeneously
developing squid. This is still one of the main bottlenecks in culturing, and a steady
supply of live, fresh, cultured food organisms (copepods, crab zoeae, mysids) can
greatly contribute to excellent survival rates on experimental level. Paralarvae feeding behaviour is noticeably experience based (Chen et al. 1996).
While food availability is essential during rearing, food quality is more important for development and growth. When squid reach 40–50 days of age (6–10 mm
ML) they require higher daily food intake, large and more energetically rewarding
prey types and more swimming space as they start swimming in schools. If these
requirements are not met, a second peak in mortality is often observed. Elucidating
ontogenetic size-specific nutritional requirements of squid is essential to improve
feeding and should be ranked as a high-priority research area.
For highly active swimmers such as loliginid squids, which begin schooling at
an early juvenile stage, sufficient tank space to allow expression of normal swimming and feeding behaviour and to accommodate relatively large groups is a major