288
E. A. G. Vidal and S. von Boletzky
damage due to abrasion that occurs when paralarvae come in contact with tank
surfaces (Vidal et al. 2002a). In addition, supplying a variety of live prey of high
nutritional quality enhances feeding of the heterogeneously developing hatchlings
by encouraging their natural hunting behaviour. The main requirements for paralarvae rearing are listed below.
16.6.1 Tank Design and Circulation Patterns
L. vulgaris and D. opalescens paralarvae have been reared in both open and closed
seawater systems (Tables 16.1 and 16.2). Boletzky and Hanlon (1983) and Hanlon
(1990) address the advantages and disadvantages of each system, with emphasis on
filtration, a fundamental element of closed systems.
A tank must provide adequate space to reduce stress of paralarvae and allow
them to express normal behaviour. Cylindrical tanks generally are preferable to
rectangular tanks, as the corners of the latter create ‘dead’ zones of poor circulation that make it more difficult to establish suitable circulation for the rearing of
paralarvae.
Early attempts to rear L. vulgaris hatchlings in a ‘bell jar holding about 25 L’
were unsuccessful, with a maximum survival of only 1 week (Portmann and Bidder
1928). Hatchlings of this species have been raised in 5-L glass cylinders (25 cm
diameter with opaque walls), either in standing seawater, partially renewed twice
daily or in slowly running seawater; and in circular 45-L polyvinyl chloride (PVC)
tanks (40 cm diameter, 40 cm deep), in slowly running seawater (Boletzky 1974a).
An experiment made under similar conditions but with continuous light and slowly
decreasing temperatures (18.5–12 °C) developed a film of red and green algae on
the inner tank surface. This presented a visual barrier that helped the animals avoid
contact with the tank walls (Boletzky 1979), thus preventing injuries, especially
abrasion of the outer rim of the fins. Reduced fin size due to abrasion prevents animals from stabilising the forward darting movement needed when attacking prey.
L. vulgaris was also reared by Turk et al. (1986) from eggs shipped in from
the Mediterranean, in Galveston (USA) in both natural and artificial seawater in a
closed system previously used by Yang et al. (1983a) for D. opalescens. To evaluate
the effect of temperature on statolith growth, Villanueva (2000a) raised L. vulgaris
paralarvae in an open system of 13-L cylindrical bags (20 cm diameter, 42 cm deep)
with constant water flow (~ 35 L h
−1
), using near-natural photoperiod with fluorescent lamps (10.3–3.3 μE m
−2
s
−1
luminosity from the top to the middle of the bags).
D. opalescens paralarvae first were reared by Hurley (1976) in a closed system of
aerated black cylindrical tanks (48 L). Subsequently, pioneering experiments were
conducted in Galveston (Hanlon et al. 1979; Yang et al. 1980, 1983a, b, 1986). The
work of Yang et al. (1983a) became the foundation for experiments with loliginids
in which paralarval rearing and growth was improved compared to previous trials.
These authors used a closed system of two relatively large tanks (1,300 L, 1.8 m
diameter, 0.75 m deep, total volume 2,600 L). One was the rearing unit and the other
the biofilter. Photoperiod was set at 17L:7D and light intensity varied between 11
E. A. G. Vidal and S. von Boletzky
damage due to abrasion that occurs when paralarvae come in contact with tank
surfaces (Vidal et al. 2002a). In addition, supplying a variety of live prey of high
nutritional quality enhances feeding of the heterogeneously developing hatchlings
by encouraging their natural hunting behaviour. The main requirements for paralarvae rearing are listed below.
16.6.1 Tank Design and Circulation Patterns
L. vulgaris and D. opalescens paralarvae have been reared in both open and closed
seawater systems (Tables 16.1 and 16.2). Boletzky and Hanlon (1983) and Hanlon
(1990) address the advantages and disadvantages of each system, with emphasis on
filtration, a fundamental element of closed systems.
A tank must provide adequate space to reduce stress of paralarvae and allow
them to express normal behaviour. Cylindrical tanks generally are preferable to
rectangular tanks, as the corners of the latter create ‘dead’ zones of poor circulation that make it more difficult to establish suitable circulation for the rearing of
paralarvae.
Early attempts to rear L. vulgaris hatchlings in a ‘bell jar holding about 25 L’
were unsuccessful, with a maximum survival of only 1 week (Portmann and Bidder
1928). Hatchlings of this species have been raised in 5-L glass cylinders (25 cm
diameter with opaque walls), either in standing seawater, partially renewed twice
daily or in slowly running seawater; and in circular 45-L polyvinyl chloride (PVC)
tanks (40 cm diameter, 40 cm deep), in slowly running seawater (Boletzky 1974a).
An experiment made under similar conditions but with continuous light and slowly
decreasing temperatures (18.5–12 °C) developed a film of red and green algae on
the inner tank surface. This presented a visual barrier that helped the animals avoid
contact with the tank walls (Boletzky 1979), thus preventing injuries, especially
abrasion of the outer rim of the fins. Reduced fin size due to abrasion prevents animals from stabilising the forward darting movement needed when attacking prey.
L. vulgaris was also reared by Turk et al. (1986) from eggs shipped in from
the Mediterranean, in Galveston (USA) in both natural and artificial seawater in a
closed system previously used by Yang et al. (1983a) for D. opalescens. To evaluate
the effect of temperature on statolith growth, Villanueva (2000a) raised L. vulgaris
paralarvae in an open system of 13-L cylindrical bags (20 cm diameter, 42 cm deep)
with constant water flow (~ 35 L h
−1
), using near-natural photoperiod with fluorescent lamps (10.3–3.3 μE m
−2
s
−1
luminosity from the top to the middle of the bags).
D. opalescens paralarvae first were reared by Hurley (1976) in a closed system of
aerated black cylindrical tanks (48 L). Subsequently, pioneering experiments were
conducted in Galveston (Hanlon et al. 1979; Yang et al. 1980, 1983a, b, 1986). The
work of Yang et al. (1983a) became the foundation for experiments with loliginids
in which paralarval rearing and growth was improved compared to previous trials.
These authors used a closed system of two relatively large tanks (1,300 L, 1.8 m
diameter, 0.75 m deep, total volume 2,600 L). One was the rearing unit and the other
the biofilter. Photoperiod was set at 17L:7D and light intensity varied between 11