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E. A. G. Vidal and S. von Boletzky
partial pressure gradient across the air–water interface (Appleford et al. 2003). Saturation is lower at high temperature, exactly when oxygen demands by respiration,
feeding and ammonia excretion increase. Therefore, when rearing at high temperatures, continual monitoring of oxygen levels is very important, as hatchlings must
be able to extract enough oxygen to match their higher metabolic demands. Special
attention must be paid at higher stocking densities.
Air bubbles (especially extra-fine bubbles) must be avoided in rearing tanks because they adhere to the skin and are trapped inside the mantle, causing entrapment of the hatchlings in the surface tension at the air–water interface. This impairs
swimming and prey capture, which increases mortality of paralarvae (E.A.G. Vidal,
personal observation). If artificial aeration is used, it should be in a separate treatment tank and not in the rearing tank (Boletzky and Hanlon 1983). Gas bubble disease can be a problem in some systems. It is caused by the supersaturation of total
dissolved gasses: oxygen, carbon dioxide, nitrogen and argon. This can result when
injecting high-pressure air at depth; when water near saturation is heated; or when
an outdoor system near supersaturation is exposed to a low-pressure weather front.
The gas bubbles so formed can adhere to hatchlings, hampering mobility in a way
that can increase mortality. In general, total gas saturation should not exceed about
105 % and is managed by degassing.
16.6.2.4 pH
pH is a critical parameter that plays a role in determining the concentrations of other
key parameters, such as the aforementioned toxic nitrogen species. As with eggs,
paralarvae are very sensitive to pH changes and it was shown that low pH values
might affect the accumulation of essential and nonessential metals in L. vulgaris
paralarvae due to the disturbance of ionic and acid–base physiological processes
(Lacoue-Labarthe et al. 2011). The ideal pH range is 8.1–8.4 (Vidal et al. 2002a),
similar to the typical values in their natural oceanic habitat.
16.6.2.5 Disinfection and Pathogens
The seawater used for rearing should pass through UV sterilization to reduce levels
of pathogenic bacteria. However, filtration to remove suspended particles should
be done before the utilization of the UV sterilizer as POM is the major substrate
for bacteria in recirculation systems (Appleford et al. 2003). UV sterilization has
been useful in minimizing bacterial infection (Hanlon 1990; Vidal et al. 2002a) and
should be employed during the rearing of paralarvae.
The surfaces of eggs and larvae are well known to be good substrates for bacterial colonization (Bergh et al. 1992) and paralarvae stressed by suboptimal conditions
are more subject to skin damage and infection. A particularly promising line-ofresearch is the interaction between paralarvae and bacteria, particularly the ability
of paralarvae to withstand pathogens.
E. A. G. Vidal and S. von Boletzky
partial pressure gradient across the air–water interface (Appleford et al. 2003). Saturation is lower at high temperature, exactly when oxygen demands by respiration,
feeding and ammonia excretion increase. Therefore, when rearing at high temperatures, continual monitoring of oxygen levels is very important, as hatchlings must
be able to extract enough oxygen to match their higher metabolic demands. Special
attention must be paid at higher stocking densities.
Air bubbles (especially extra-fine bubbles) must be avoided in rearing tanks because they adhere to the skin and are trapped inside the mantle, causing entrapment of the hatchlings in the surface tension at the air–water interface. This impairs
swimming and prey capture, which increases mortality of paralarvae (E.A.G. Vidal,
personal observation). If artificial aeration is used, it should be in a separate treatment tank and not in the rearing tank (Boletzky and Hanlon 1983). Gas bubble disease can be a problem in some systems. It is caused by the supersaturation of total
dissolved gasses: oxygen, carbon dioxide, nitrogen and argon. This can result when
injecting high-pressure air at depth; when water near saturation is heated; or when
an outdoor system near supersaturation is exposed to a low-pressure weather front.
The gas bubbles so formed can adhere to hatchlings, hampering mobility in a way
that can increase mortality. In general, total gas saturation should not exceed about
105 % and is managed by degassing.
16.6.2.4 pH
pH is a critical parameter that plays a role in determining the concentrations of other
key parameters, such as the aforementioned toxic nitrogen species. As with eggs,
paralarvae are very sensitive to pH changes and it was shown that low pH values
might affect the accumulation of essential and nonessential metals in L. vulgaris
paralarvae due to the disturbance of ionic and acid–base physiological processes
(Lacoue-Labarthe et al. 2011). The ideal pH range is 8.1–8.4 (Vidal et al. 2002a),
similar to the typical values in their natural oceanic habitat.
16.6.2.5 Disinfection and Pathogens
The seawater used for rearing should pass through UV sterilization to reduce levels
of pathogenic bacteria. However, filtration to remove suspended particles should
be done before the utilization of the UV sterilizer as POM is the major substrate
for bacteria in recirculation systems (Appleford et al. 2003). UV sterilization has
been useful in minimizing bacterial infection (Hanlon 1990; Vidal et al. 2002a) and
should be employed during the rearing of paralarvae.
The surfaces of eggs and larvae are well known to be good substrates for bacterial colonization (Bergh et al. 1992) and paralarvae stressed by suboptimal conditions
are more subject to skin damage and infection. A particularly promising line-ofresearch is the interaction between paralarvae and bacteria, particularly the ability
of paralarvae to withstand pathogens.