277
16 Loligo vulgaris and Doryteuthis opalescens
cephalopods. Zeidberg (2008) reports that in D. opalescens mating groups involved
10–20 individuals and had a sex ratio of 1–2 males for each female. Although
sneaker mating has been observed in other species of Doryteuthis and Loligo, so far
no such reports exist for L. vulgaris. However, Zeidberg (2008) considers that multiple paternity in individual egg capsules may be common in most loliginid squids.
16.3.3 Physical and Chemical Parameters
Natural or synthetic seawater of high quality is indispensable for cephalopod
broodstock maintenance, rearing and culture. A salinity between 34 and 38 psu is
recommended, with pH around 8 (7.7–8.2) and O 2 levels close to saturation (5 mg
L
–1
), along with levels of ammonia and nitrite < 0.1 mg L
–1
, and < 20 mg L
–1
for nitrate are considered normal (Boletzky and Hanlon 1983). Water temperature should
best be maintained between 12 and 22°C in culture systems for the two species
considered here.
16.4 Spawning Process
The structure of the egg capsules in both species is essentially as described by
Jecklin (1934), but the way these capsules are deposited is different. In L. vulgaris,
the egg capsules are always suspended in dense clusters from overhanging substrates (Boletzky 1974a), whereas in D. opalescens, they are deposited on (generally soft) bottoms (Fields 1965). Spawning can be stimulated by the visualization of
natural or artificial egg masses in the tanks (Arnold 1962).
An open question remains with regard to the actual making of an egg capsule
by the spawning female: Is the spirally coiled string of eggs embedded in oviducal
jelly released along with the outer capsule, the material of which is produced by the
nidamental glands, or is the outer capsule released first and the egg string ‘pumped’
into it, as described by Zeidberg (2008)?
Ideally, females spawning in a tank should remain in contact with other adult individuals (Hanlon 1990), to be able to regularly feed, mate and lay eggs (Fig. 16.1).
However, if mating males are generating too much stress for spawning females,
they should be separated.
16.5 Embryonic Development
Egg care is one of the most important steps for rearing success. During embryogenesis, eggs should be closely monitored to evaluate progress of development and
proximity of hatching. Naef (1928) and Arnold (1965) provided embryonic developmental scales for loliginids and the latter scale is used as reference in this chapter.
16 Loligo vulgaris and Doryteuthis opalescens
cephalopods. Zeidberg (2008) reports that in D. opalescens mating groups involved
10–20 individuals and had a sex ratio of 1–2 males for each female. Although
sneaker mating has been observed in other species of Doryteuthis and Loligo, so far
no such reports exist for L. vulgaris. However, Zeidberg (2008) considers that multiple paternity in individual egg capsules may be common in most loliginid squids.
16.3.3 Physical and Chemical Parameters
Natural or synthetic seawater of high quality is indispensable for cephalopod
broodstock maintenance, rearing and culture. A salinity between 34 and 38 psu is
recommended, with pH around 8 (7.7–8.2) and O 2 levels close to saturation (5 mg
L
–1
), along with levels of ammonia and nitrite < 0.1 mg L
–1
, and < 20 mg L
–1
for nitrate are considered normal (Boletzky and Hanlon 1983). Water temperature should
best be maintained between 12 and 22°C in culture systems for the two species
considered here.
16.4 Spawning Process
The structure of the egg capsules in both species is essentially as described by
Jecklin (1934), but the way these capsules are deposited is different. In L. vulgaris,
the egg capsules are always suspended in dense clusters from overhanging substrates (Boletzky 1974a), whereas in D. opalescens, they are deposited on (generally soft) bottoms (Fields 1965). Spawning can be stimulated by the visualization of
natural or artificial egg masses in the tanks (Arnold 1962).
An open question remains with regard to the actual making of an egg capsule
by the spawning female: Is the spirally coiled string of eggs embedded in oviducal
jelly released along with the outer capsule, the material of which is produced by the
nidamental glands, or is the outer capsule released first and the egg string ‘pumped’
into it, as described by Zeidberg (2008)?
Ideally, females spawning in a tank should remain in contact with other adult individuals (Hanlon 1990), to be able to regularly feed, mate and lay eggs (Fig. 16.1).
However, if mating males are generating too much stress for spawning females,
they should be separated.
16.5 Embryonic Development
Egg care is one of the most important steps for rearing success. During embryogenesis, eggs should be closely monitored to evaluate progress of development and
proximity of hatching. Naef (1928) and Arnold (1965) provided embryonic developmental scales for loliginids and the latter scale is used as reference in this chapter.