439
23 Octopus vulgaris. Paralarval Culture
23.4.3.3 Temperature
The change of temperature between the broodstock tank and the paralarvae rearing
tank must be gradual (an increase of approximately 1°C per day). Temperature is
the most important determinant of development and growth of paralarvae (Mangold
and Boletzky 1973). Paralarval rearing temperatures cited in the literature range
between 19 and 25 ºC (Iglesias et al. 2007), but temperatures of 20–22 ºC are recommended to obtain optimal growth and survival. High daily temperature fluctuations
should be avoided during paralarval culture.
23.4.3.4 Chemical Parameters
The most important water quality parameters in the larval rearing phase are salinity,
pH and concentrations of dissolved oxygen, ammonia, nitrite and nitrate.
Octopuses show very low tolerance to low salinity; therefore, seawater of around
32–35 psu should be used. Salinity should be as constant as possible because sudden changes are not tolerated by paralarvae. Rearing places close to rivers and
freshwater sources need to take into account this parameter.
Dissolved oxygen is crucial for gas exchanges and depends on temperature.
Optimal levels in the paralarvae rearing process should be kept between 6 and
8 mg L
−1
, but should not be allowed to fall below 4 mg L
−1
. Cerezo-Valverde and
García-García (2005) determined optimal oxygen saturation levels for subadult and
adult individuals to be between 100 and 65 % and suboptimal saturation levels between 65 and 35 % (dangerous below 35 %) for temperatures between 17 and 20 ºC.
pH, nitrite and ammonia levels need to be monitored according to water renewal
but at least once a week. Feyjoo et al. (2011) determined the acute toxicity of unionized ammonia and nitrite on newly hatched O� vulgaris paralarvae. The lethal concentration 50 (LC50) value after 24 h of exposure was 10.7 ppm for ammonia and
19.9 ppm for nitrite. This suggests that paralarvae are quite resistant to free ammonia compared to marine fish larvae, but much less resistant to nitrite. At concentrations much lower than the LC50 values, negative effects are observed on both prey
intake and chromatophore activity (Feyjoo et al. 2011).
Gas supersaturation can explain the extensive mortality that sometimes happens
during the early life stages in intensive production of marine species (Gunnarsli
et al. 2008). Air bubbles can be formed in gills, fins, skin and blood of fishes (gas
bubble trauma), whilst in the case of O� vulgaris paralarvae, bubbles usually appear inside the mantle cavity. This phenomenon can be related to water circulation,
temperature and chemical parameters; for example, it can appear through the mechanical process of heating the water, long pipe runs, pump cavitation, etc. In order
to prevent water supersaturation (mainly nitrogen gas), it is recommended to have
a method of trickling water over a large surface area, as in a packed-column aerator
(Hargreaves and Tucker 1999).
23 Octopus vulgaris. Paralarval Culture
23.4.3.3 Temperature
The change of temperature between the broodstock tank and the paralarvae rearing
tank must be gradual (an increase of approximately 1°C per day). Temperature is
the most important determinant of development and growth of paralarvae (Mangold
and Boletzky 1973). Paralarval rearing temperatures cited in the literature range
between 19 and 25 ºC (Iglesias et al. 2007), but temperatures of 20–22 ºC are recommended to obtain optimal growth and survival. High daily temperature fluctuations
should be avoided during paralarval culture.
23.4.3.4 Chemical Parameters
The most important water quality parameters in the larval rearing phase are salinity,
pH and concentrations of dissolved oxygen, ammonia, nitrite and nitrate.
Octopuses show very low tolerance to low salinity; therefore, seawater of around
32–35 psu should be used. Salinity should be as constant as possible because sudden changes are not tolerated by paralarvae. Rearing places close to rivers and
freshwater sources need to take into account this parameter.
Dissolved oxygen is crucial for gas exchanges and depends on temperature.
Optimal levels in the paralarvae rearing process should be kept between 6 and
8 mg L
−1
, but should not be allowed to fall below 4 mg L
−1
. Cerezo-Valverde and
García-García (2005) determined optimal oxygen saturation levels for subadult and
adult individuals to be between 100 and 65 % and suboptimal saturation levels between 65 and 35 % (dangerous below 35 %) for temperatures between 17 and 20 ºC.
pH, nitrite and ammonia levels need to be monitored according to water renewal
but at least once a week. Feyjoo et al. (2011) determined the acute toxicity of unionized ammonia and nitrite on newly hatched O� vulgaris paralarvae. The lethal concentration 50 (LC50) value after 24 h of exposure was 10.7 ppm for ammonia and
19.9 ppm for nitrite. This suggests that paralarvae are quite resistant to free ammonia compared to marine fish larvae, but much less resistant to nitrite. At concentrations much lower than the LC50 values, negative effects are observed on both prey
intake and chromatophore activity (Feyjoo et al. 2011).
Gas supersaturation can explain the extensive mortality that sometimes happens
during the early life stages in intensive production of marine species (Gunnarsli
et al. 2008). Air bubbles can be formed in gills, fins, skin and blood of fishes (gas
bubble trauma), whilst in the case of O� vulgaris paralarvae, bubbles usually appear inside the mantle cavity. This phenomenon can be related to water circulation,
temperature and chemical parameters; for example, it can appear through the mechanical process of heating the water, long pipe runs, pump cavitation, etc. In order
to prevent water supersaturation (mainly nitrogen gas), it is recommended to have
a method of trickling water over a large surface area, as in a packed-column aerator
(Hargreaves and Tucker 1999).