7
(F1, F2, F3…). Subsequent reproduction of a few individuals brought up in the
first rearing experiment may suffice for some generations, but sooner or later
inbreeding may generate negative effects (Andrade et al. 2012). This will necessitate the occasional introduction of new genitors from wild populations. Cephalopods have a single period of sexual maturity, spawning single- or multiple-egg
masses during a more or less protracted period of maturity. Thus, the question
arises whether during culture experiments the brooding stock should be replaced
by new individuals every new season or period. When live genitors (or egg masses
with viable embryos) are not available, an alternative method to start a culture may
be the collection of ova and spermatozoa from freshly caught, mature individuals,
followed by in vitro fertilization. An essential condition for normal development
of these embryos is the preparation of an oviducal jelly layer embedding the eggs
(Ikeda et al. 1993). This allows the chorion membrane to expand, thus providing the
necessary perivitelline space for the developing embryo. This method allowed the
fertilization of 12 oceanic squid species (Villanueva et al. 2012) in view of the difficulties involved in obtaining eggs from spawning of captive oceanic squid broodstock maintained in aquaria (Bower and Sakurai 1996; O’Dor and Balch 1985).
When weighing the pros and cons of candidate species for culture, one should
remember that the reproductive behaviours (Hanlon and Messenger 1996) and
related features of anatomy and functional morphology (Budelmann et al. 1997)
vary greatly among systematic groups of cephalopods, especially with regard to their
respective ecological adaptations and lifestyles. There are numerous ways how spermatozoids are packed in spermatophores, which are produced by glands of the male
duct; how these packages are transferred to a chosen female during mating; and how
a spermatophore is transformed into a bubble-shaped spermatangium that may be
stored by the female (in special places of the integument, or in pouches, or—in the
case of octopods—in the oviduct or even in the ovary itself; Nesis 1996). Particularly complex mechanisms allow the spermatozoa to be finally released from their storage sites and activated so that they can pass through the micropyle of an egg chorion.
The ostensibly simple mating system of cephalopods (one female, one male)
may be subject to considerable complications. Thus, the basic mating pattern may
be modified by the actions of sneaker males or by other mechanisms of sperm
competition (Hanlon and Messenger 1996; Huffard et al. 2008; Sato et al. 2010;
Iwata et al. 2011). The observation of multiple paternity in hatchlings from a single
egg mass suggests that this ‘complication’ is an important advantage for natural
selection, though a bad one for aquaculture (Boyle et al. 2001; Buresch et al. 2003;
Nesis 1996; Hoving et al. 2010; Voight 2001; Voight and Feldheim 2009; Quinteiro
et al. 2011). Recent observations on Loligo bleekeri show that males of different
sizes that employ different mating behaviours also produce two different forms of
spermatozoa (Iwata et al. 2011).
Mating and spawning in captivity may generate some stress for the females if
males have continuous access to them. Since females store the sperm after each
mating in sufficient amounts to last for weeks or months, it is advisable to keep
mature males separate from spawning females. Spawning is indeed of high energy
cost for both males (Franklin et al. 2012) and females, especially if the female
produces large masses of eggs with gelatinous egg case material, either continually
1 Cephalopod Biology
(F1, F2, F3…). Subsequent reproduction of a few individuals brought up in the
first rearing experiment may suffice for some generations, but sooner or later
inbreeding may generate negative effects (Andrade et al. 2012). This will necessitate the occasional introduction of new genitors from wild populations. Cephalopods have a single period of sexual maturity, spawning single- or multiple-egg
masses during a more or less protracted period of maturity. Thus, the question
arises whether during culture experiments the brooding stock should be replaced
by new individuals every new season or period. When live genitors (or egg masses
with viable embryos) are not available, an alternative method to start a culture may
be the collection of ova and spermatozoa from freshly caught, mature individuals,
followed by in vitro fertilization. An essential condition for normal development
of these embryos is the preparation of an oviducal jelly layer embedding the eggs
(Ikeda et al. 1993). This allows the chorion membrane to expand, thus providing the
necessary perivitelline space for the developing embryo. This method allowed the
fertilization of 12 oceanic squid species (Villanueva et al. 2012) in view of the difficulties involved in obtaining eggs from spawning of captive oceanic squid broodstock maintained in aquaria (Bower and Sakurai 1996; O’Dor and Balch 1985).
When weighing the pros and cons of candidate species for culture, one should
remember that the reproductive behaviours (Hanlon and Messenger 1996) and
related features of anatomy and functional morphology (Budelmann et al. 1997)
vary greatly among systematic groups of cephalopods, especially with regard to their
respective ecological adaptations and lifestyles. There are numerous ways how spermatozoids are packed in spermatophores, which are produced by glands of the male
duct; how these packages are transferred to a chosen female during mating; and how
a spermatophore is transformed into a bubble-shaped spermatangium that may be
stored by the female (in special places of the integument, or in pouches, or—in the
case of octopods—in the oviduct or even in the ovary itself; Nesis 1996). Particularly complex mechanisms allow the spermatozoa to be finally released from their storage sites and activated so that they can pass through the micropyle of an egg chorion.
The ostensibly simple mating system of cephalopods (one female, one male)
may be subject to considerable complications. Thus, the basic mating pattern may
be modified by the actions of sneaker males or by other mechanisms of sperm
competition (Hanlon and Messenger 1996; Huffard et al. 2008; Sato et al. 2010;
Iwata et al. 2011). The observation of multiple paternity in hatchlings from a single
egg mass suggests that this ‘complication’ is an important advantage for natural
selection, though a bad one for aquaculture (Boyle et al. 2001; Buresch et al. 2003;
Nesis 1996; Hoving et al. 2010; Voight 2001; Voight and Feldheim 2009; Quinteiro
et al. 2011). Recent observations on Loligo bleekeri show that males of different
sizes that employ different mating behaviours also produce two different forms of
spermatozoa (Iwata et al. 2011).
Mating and spawning in captivity may generate some stress for the females if
males have continuous access to them. Since females store the sperm after each
mating in sufficient amounts to last for weeks or months, it is advisable to keep
mature males separate from spawning females. Spawning is indeed of high energy
cost for both males (Franklin et al. 2012) and females, especially if the female
produces large masses of eggs with gelatinous egg case material, either continually
1 Cephalopod Biology