293
16 Loligo vulgaris and Doryteuthis opalescens
16.6.2.6 Temperature
L. vulgaris paralarvae have been reared from 11 to 22°C (Boletzky 1974a; Villanueva
2000a) and D. opalescens from 12 to 18°C (Vidal et al. 2002b; Chen et al. 1996)
(Tables 16.1 and 16.2). Interestingly, L. vulgaris hatchlings showed lower thermal
tolerance than the embryos. This was attributed mainly to the greater oxygen demand of the highly active hatchlings. In addition, thermal tolerance of hatchlings
increased with temperature, with LT50 (temperature at which 50 % of hatchlings
had died) values of 31 and 33°C from hatchlings incubated at 13 and 19 °C, respectively (Rosa et al. 2012).
Despite our current deficiencies in establishing realistic criteria on tolerance
and chronic toxicity limits for loliginid hatchlings, as indicated above, available
information provides essential features for the main factors required in successful
rearing.
16.6.3 Food and Feeding
In the first days after hatching (dah), paralarvae combine both endogenous (yolk)
and exogenous (prey) energy sources (Boletzky 1975; Vidal et al. 2002b). The yolk
content at the moment of hatching although highly variable seems to be proportional to the body mass, representing 33–63 % of body dw and 10–18 % of body wet
weight (ww) of paralarvae. The time required to exhaust yolk reserves decreases
exponentially with increasing temperature. For example, D. opalescens hatchlings
can survive longer (6 days) on their yolk reserve at 12°C than at 16°C (4 days; with
80 % mortality, Vidal et al. 2002b). Clearly, the yolk reserve must fuel metabolism
while the prey capture skills of paralarvae are still developing. This implies that the
‘window of opportunity’ is very short and hatchlings must quickly capture sufficient
food to meet their high metabolic demands (Vidal et al. 2002b; Rosa et al. 2012).
Accordingly, it was shown that early D. opalescens paralarvae are unable to withstand even short periods of food deprivation, being extremely sensitive to starvation
(Vidal et al. 2006). This is consistent with the high mortality rates observed during
the first 10 dah for both L. vulgaris and D. opalescens that delimits the critical
transition period from yolk absorption to successful prey capture (Vecchione 1987;
Villanueva 2000a; Vidal et al. 2002b).
Extra care should be taken to provide food of adequate type and size, high nutritional quality and in sufficient quantities to the newly hatched paralarvae. Delaying
first feeding will most certainly increase mortality due to energy deficit and starvation.
It has been recognized that the first prey items a hatchling encounters are decisive
for the immediate predatory success or failure and the subsequent neurophysiologic
development and learning processes in the young predator (Chen et al. 1996; Preuss
and Gilly 2000). The catchability of such prey may be defined in relation to its escape
response, its defensive equipment (e.g. spiny integuments) acting after seizure, and
ultimately its resistance to attempted ingestion (hard carapaces, etc.).
16 Loligo vulgaris and Doryteuthis opalescens
16.6.2.6 Temperature
L. vulgaris paralarvae have been reared from 11 to 22°C (Boletzky 1974a; Villanueva
2000a) and D. opalescens from 12 to 18°C (Vidal et al. 2002b; Chen et al. 1996)
(Tables 16.1 and 16.2). Interestingly, L. vulgaris hatchlings showed lower thermal
tolerance than the embryos. This was attributed mainly to the greater oxygen demand of the highly active hatchlings. In addition, thermal tolerance of hatchlings
increased with temperature, with LT50 (temperature at which 50 % of hatchlings
had died) values of 31 and 33°C from hatchlings incubated at 13 and 19 °C, respectively (Rosa et al. 2012).
Despite our current deficiencies in establishing realistic criteria on tolerance
and chronic toxicity limits for loliginid hatchlings, as indicated above, available
information provides essential features for the main factors required in successful
rearing.
16.6.3 Food and Feeding
In the first days after hatching (dah), paralarvae combine both endogenous (yolk)
and exogenous (prey) energy sources (Boletzky 1975; Vidal et al. 2002b). The yolk
content at the moment of hatching although highly variable seems to be proportional to the body mass, representing 33–63 % of body dw and 10–18 % of body wet
weight (ww) of paralarvae. The time required to exhaust yolk reserves decreases
exponentially with increasing temperature. For example, D. opalescens hatchlings
can survive longer (6 days) on their yolk reserve at 12°C than at 16°C (4 days; with
80 % mortality, Vidal et al. 2002b). Clearly, the yolk reserve must fuel metabolism
while the prey capture skills of paralarvae are still developing. This implies that the
‘window of opportunity’ is very short and hatchlings must quickly capture sufficient
food to meet their high metabolic demands (Vidal et al. 2002b; Rosa et al. 2012).
Accordingly, it was shown that early D. opalescens paralarvae are unable to withstand even short periods of food deprivation, being extremely sensitive to starvation
(Vidal et al. 2006). This is consistent with the high mortality rates observed during
the first 10 dah for both L. vulgaris and D. opalescens that delimits the critical
transition period from yolk absorption to successful prey capture (Vecchione 1987;
Villanueva 2000a; Vidal et al. 2002b).
Extra care should be taken to provide food of adequate type and size, high nutritional quality and in sufficient quantities to the newly hatched paralarvae. Delaying
first feeding will most certainly increase mortality due to energy deficit and starvation.
It has been recognized that the first prey items a hatchling encounters are decisive
for the immediate predatory success or failure and the subsequent neurophysiologic
development and learning processes in the young predator (Chen et al. 1996; Preuss
and Gilly 2000). The catchability of such prey may be defined in relation to its escape
response, its defensive equipment (e.g. spiny integuments) acting after seizure, and
ultimately its resistance to attempted ingestion (hard carapaces, etc.).