301
16 Loligo vulgaris and Doryteuthis opalescens
underscore the importance of elucidating ontogenetic size-specific nutritional requirements of paralarvae to improve feeding and should be ranked as a high-priority
research area.
16.6.4 Survival
L. vulgaris hatched from egg masses in the laboratory were raised by Boletzky
(1974a) to a maximum of 45 days and subsequently to 70 days of age (Boletzky
1979) (Table 16.1). Turk et al. (1986) reared L. vulgaris, hatched from eggs shipped
in from the Mediterranean, in Galveston, recording high mortality rates (90 %) in
the first 10 dah, with the last surviving squid reaching 140 days of age (Table 16.1).
To assess the effect of temperature on growth of paralarvae and their statoliths,
Villanueva (2000a) reared this species up to 62 and 50 dah at a mean temperature of
11 and 19 °C, respectively. Survival rates ranged from 0.2 to 1.4 % and were likely
affected by the tetracycline staining procedure used.
Hurley (1976) and Hanlon et al. (1979) were the first to rear D. opalescens to
a maximum age of 100 and 79 days, respectively, with survival rates of 1–12 % at
70 dah (Table 16.2). Subsequently, best results were obtained by Yang et al. (1980,
1983a, b, 1986) with survival rates of 25 % at 60 dah. To study the development of
circular mantle muscles and the giant axon system control over both prey capture
and escape behaviour of paralarvae, Preuss et al. (1997) and Preuss and Gilly (2000)
raised D. opalescens paralarvae up to 60 dah, but no information is given on the
survival rates.
By refining rearing methodology, Vidal et al. (2002a) were able to obtain survival rates of 70–78 % at day 10 and of 42–60 % during the first 60 dah (Table 16.2).
This was a step forward when compared with the best previous results of only 25 %
during the same period, thus offering new possibilities for squid culture. The main
factors that contribute to the high survival rates obtained were attributed mainly
to: (1) stabilising water quality parameters; (2) offering a combination of live prey
types of different sizes and including enriched Artemia nauplii to overcome problems of prey availability; (3) keeping prey density above 50 prey L
−1
at all times; (4)
feeding small amounts of food at regular intervals; and (5) reducing turbulence and
maintaining current speed inside the tanks between 1.0 and 1.4 cm s
−1
.
A common pattern emerges from the aforementioned experiments, showing that
the highest mortality rates occur during the first 10–15 dah and are primarily a consequence of the critical transition between full yolk absorption and successful prey
capture (Hanlon 1987; Villanueva 2000a; Vidal et al. 2002a, b). Survival level after
this period and thereafter remains relatively steady until day 45–70 (Hanlon 1987;
Vidal et al. 2002a), when it again decreases. This second peak in mortality could be a
consequence of inadequate diet due to the lack of appropriate sized food and a need for
larger tanks. By this age, squid have a mean ML of about 6–11 mm and require higher
daily food intake, larger prey types and more swimming space as they start swimming
in schools.
16 Loligo vulgaris and Doryteuthis opalescens
underscore the importance of elucidating ontogenetic size-specific nutritional requirements of paralarvae to improve feeding and should be ranked as a high-priority
research area.
16.6.4 Survival
L. vulgaris hatched from egg masses in the laboratory were raised by Boletzky
(1974a) to a maximum of 45 days and subsequently to 70 days of age (Boletzky
1979) (Table 16.1). Turk et al. (1986) reared L. vulgaris, hatched from eggs shipped
in from the Mediterranean, in Galveston, recording high mortality rates (90 %) in
the first 10 dah, with the last surviving squid reaching 140 days of age (Table 16.1).
To assess the effect of temperature on growth of paralarvae and their statoliths,
Villanueva (2000a) reared this species up to 62 and 50 dah at a mean temperature of
11 and 19 °C, respectively. Survival rates ranged from 0.2 to 1.4 % and were likely
affected by the tetracycline staining procedure used.
Hurley (1976) and Hanlon et al. (1979) were the first to rear D. opalescens to
a maximum age of 100 and 79 days, respectively, with survival rates of 1–12 % at
70 dah (Table 16.2). Subsequently, best results were obtained by Yang et al. (1980,
1983a, b, 1986) with survival rates of 25 % at 60 dah. To study the development of
circular mantle muscles and the giant axon system control over both prey capture
and escape behaviour of paralarvae, Preuss et al. (1997) and Preuss and Gilly (2000)
raised D. opalescens paralarvae up to 60 dah, but no information is given on the
survival rates.
By refining rearing methodology, Vidal et al. (2002a) were able to obtain survival rates of 70–78 % at day 10 and of 42–60 % during the first 60 dah (Table 16.2).
This was a step forward when compared with the best previous results of only 25 %
during the same period, thus offering new possibilities for squid culture. The main
factors that contribute to the high survival rates obtained were attributed mainly
to: (1) stabilising water quality parameters; (2) offering a combination of live prey
types of different sizes and including enriched Artemia nauplii to overcome problems of prey availability; (3) keeping prey density above 50 prey L
−1
at all times; (4)
feeding small amounts of food at regular intervals; and (5) reducing turbulence and
maintaining current speed inside the tanks between 1.0 and 1.4 cm s
−1
.
A common pattern emerges from the aforementioned experiments, showing that
the highest mortality rates occur during the first 10–15 dah and are primarily a consequence of the critical transition between full yolk absorption and successful prey
capture (Hanlon 1987; Villanueva 2000a; Vidal et al. 2002a, b). Survival level after
this period and thereafter remains relatively steady until day 45–70 (Hanlon 1987;
Vidal et al. 2002a), when it again decreases. This second peak in mortality could be a
consequence of inadequate diet due to the lack of appropriate sized food and a need for
larger tanks. By this age, squid have a mean ML of about 6–11 mm and require higher
daily food intake, larger prey types and more swimming space as they start swimming
in schools.