303
16 Loligo vulgaris and Doryteuthis opalescens
Temperature exerts an instantaneous and extreme effect on growth rate of cephalopods and this is particularly true during early life when the highest growth rates
are registered (Tables 16.1 and 16.2). The influences of temperature on metabolic
rates govern growth and food conversion efficiencies. Activity or stress may impact
growth at different temperatures as a result of increased energy demand. Nevertheless, growth rates should increase up to an optimum with temperature, above which
energy requirements will be too high to maintain feed conversion and other metabolic processes and growth rates will be reduced.
While it is useful to determine optimum temperatures for growth, it is also very
important to know the tolerance limits. This is because the range of temperature
(and salinity) tolerances for growth is usually narrower than that for survival. Salinity also influences thermal response: optimal temperature seems to be lower at lower
salinities, and this naturally affects development and growth rates, as observed for
the hatching rates of S. officinalis (see Table 1 in Palmegiano and D’Apote 1983)
and L. vulgaris (Sen 2004, 2005a). It is important to emphasize that ideal temperatures for growth vary with life stage and many biological (e.g. diet, crowding) and
abiotic factors (e.g. salinity, light), as well as, their many interactions.
Fed ad libitum in the laboratory, hatchlings of D. opalescens showed exponential
growth rates during the first 20 dah that were more than twofold higher at 16°C
(7.4 % body ww day
−1
) than at 12 °C (3.3 % body ww day
−1
; Vidal 2002b). As a
consequence, small squid hatching at high temperatures (2.5 mm ML) soon attain
larger sizes than larger squid (3.0 mm ML) hatching at lower temperatures. Growth
in size during the same period was 2.4 % ML day
−1
(Tables 16.1 and 16.2).
By day 15, at the higher temperature, paralarvae were almost threefold heavier
than the newly hatched squid and at day 60, squid were growing more rapidly in
length and in mass, as paralarvae were transforming to the arrow-shaped adult form.
Mean body dw reached 16.5 mg and mean ML 14 mm. Thus, during the first 60
days of life, D. opalescens hatchlings double their mean dw five times and mean
ML twice, every 12 and 31 days, respectively (Vidal et al. 2002b; E.A.G.Vidal unpublished data). Hurley (1976) obtained highly variable growth rates (0.5–4.5 mm
ML day
−1
) rearing D. opalescens for the first 3 months after hatching on a diet
composed of Artemia nauplii and adults, while Yang et al. (1983a, 1986) obtained
exponential growth rates of 5.6 to 8.4 ww day
−1
and 2.1 ML day
−1
for D. opalescens
during the first 2 months of life at 15 °C (Table 16.2).
Very similar results were obtained by Villanueva (2000a) for L. vulgaris reared at
11 and 19 °C for 62–50 dah. Growth rates were 3.6 ww day
−1
and 1.3 mm ML day
−1
at 11°C and 7.8 ww day
−1
and 2.6 mm ML day
−1
at 19 °C (Table 16.1). Paralarvae
subjected to the higher temperature grew faster and showed final mean weight five
times higher than those reared at the lower temperature. At the coldest temperature,
L. vulgaris paralarvae doubled their ww at every 19 days; as a result, after a period
of 50 days they attained 32.7 mg and 6.3 mm ML. However, at the warmest temperature, they doubled their ww at every 9 days, attaining 157 mg and 11.7 mm ML
at the same time period (Villanueva 2000a).
Recent studies on the effects of starvation and recovery on survival, growth
and RNA/DNA ratio of D. opalescens paralarvae have demonstrated that food
16 Loligo vulgaris and Doryteuthis opalescens
Temperature exerts an instantaneous and extreme effect on growth rate of cephalopods and this is particularly true during early life when the highest growth rates
are registered (Tables 16.1 and 16.2). The influences of temperature on metabolic
rates govern growth and food conversion efficiencies. Activity or stress may impact
growth at different temperatures as a result of increased energy demand. Nevertheless, growth rates should increase up to an optimum with temperature, above which
energy requirements will be too high to maintain feed conversion and other metabolic processes and growth rates will be reduced.
While it is useful to determine optimum temperatures for growth, it is also very
important to know the tolerance limits. This is because the range of temperature
(and salinity) tolerances for growth is usually narrower than that for survival. Salinity also influences thermal response: optimal temperature seems to be lower at lower
salinities, and this naturally affects development and growth rates, as observed for
the hatching rates of S. officinalis (see Table 1 in Palmegiano and D’Apote 1983)
and L. vulgaris (Sen 2004, 2005a). It is important to emphasize that ideal temperatures for growth vary with life stage and many biological (e.g. diet, crowding) and
abiotic factors (e.g. salinity, light), as well as, their many interactions.
Fed ad libitum in the laboratory, hatchlings of D. opalescens showed exponential
growth rates during the first 20 dah that were more than twofold higher at 16°C
(7.4 % body ww day
−1
) than at 12 °C (3.3 % body ww day
−1
; Vidal 2002b). As a
consequence, small squid hatching at high temperatures (2.5 mm ML) soon attain
larger sizes than larger squid (3.0 mm ML) hatching at lower temperatures. Growth
in size during the same period was 2.4 % ML day
−1
(Tables 16.1 and 16.2).
By day 15, at the higher temperature, paralarvae were almost threefold heavier
than the newly hatched squid and at day 60, squid were growing more rapidly in
length and in mass, as paralarvae were transforming to the arrow-shaped adult form.
Mean body dw reached 16.5 mg and mean ML 14 mm. Thus, during the first 60
days of life, D. opalescens hatchlings double their mean dw five times and mean
ML twice, every 12 and 31 days, respectively (Vidal et al. 2002b; E.A.G.Vidal unpublished data). Hurley (1976) obtained highly variable growth rates (0.5–4.5 mm
ML day
−1
) rearing D. opalescens for the first 3 months after hatching on a diet
composed of Artemia nauplii and adults, while Yang et al. (1983a, 1986) obtained
exponential growth rates of 5.6 to 8.4 ww day
−1
and 2.1 ML day
−1
for D. opalescens
during the first 2 months of life at 15 °C (Table 16.2).
Very similar results were obtained by Villanueva (2000a) for L. vulgaris reared at
11 and 19 °C for 62–50 dah. Growth rates were 3.6 ww day
−1
and 1.3 mm ML day
−1
at 11°C and 7.8 ww day
−1
and 2.6 mm ML day
−1
at 19 °C (Table 16.1). Paralarvae
subjected to the higher temperature grew faster and showed final mean weight five
times higher than those reared at the lower temperature. At the coldest temperature,
L. vulgaris paralarvae doubled their ww at every 19 days; as a result, after a period
of 50 days they attained 32.7 mg and 6.3 mm ML. However, at the warmest temperature, they doubled their ww at every 9 days, attaining 157 mg and 11.7 mm ML
at the same time period (Villanueva 2000a).
Recent studies on the effects of starvation and recovery on survival, growth
and RNA/DNA ratio of D. opalescens paralarvae have demonstrated that food