depending on the oxygen saturation of the water (Daniels and Watanabe 2010).
Although the oxygen saturation in the German Bight is very high below 10 m
depth, temperatures in extreme years can reach values outside of the physiological
capacity of H. hippoglossus. Furthermore, Atlantic halibut is sensitive to strong
currents and turbidity (Buck et al. 2012). For offshore site selection, it is important
to identify an area with a sufficient supply of oxygen, a moderate temperature
regime as well as low current flow and turbidity.
11.3.4.4 Candidate: Scophthalmus maximus
The turbot is one of the most valuable food fish of the North-East Atlantic. Since
the 1990s, intensive production methods are established for all stages of life of this
species (Moksness et al. 2004). Today, the on-growing of turbot takes place mainly
in land-based recirculating aquaculture systems. S. maximus can be held in very
high stocking densities at optimum parameters (Daniels and Watanabe 2010). The
culture in surface cages, or submersible cages, was successfully demonstrated at
moderate velocities and a constant temperature regime (Daniels and Watanabe
2010). Since the growth of turbot rapidly decreases below 14 °C and above 20 °C
and it stops feeding below 8 °C and above 22 °C, the temperature conditions in the
German-Bight do not favour on-growing year-round (Person-Le Ruyet et al. 2006;
Daniels and Watanabe 2010). In addition, this species is sensitive to the tide flow
rates of up to 1.2 ms
−1 (Buck 2002), which plays an important role for site selection
in the German Bight (Buck et al. 2012).
Taking the results of current velocities and waves on cages and the nets (see
Sect. 11.4 “Technologies” below) into account a further test was conducted to proof
the behaviour of the culture candidates living in these high energy environments.
These tests were conducted at the ZAF (Zentrum für Aquakulturforschung/Center
for Aquaculture Research) under the umbrella of the AWI. A cage prototype
(Fig. 11.18b, c) was manufactured and installed in a large raceway of a RAS
(Recirculating Aquaculture System) including a water treatment device (drum filter,
nitrifying and denitrifying filter, and protein skimmer) to guarantee best water
quality during the experiment. This cylindrical cage (see section above) was
mounted in a way that an adjustable pump (Hydor Koralia magnum 5, flow rate
6,500 l/h) induced a certain current velocity on the cage and its inner culture space.
The cylinder cage in a size of 1:40 was taken from the current flume/wave tank
investigations in Hanover.
The challenge in the subproject of Project No. 13 “Open Ocean Multi-Use” was
to find fish species in small size to be used as model organism, such as juvenile
turbots with a mean size of approx. 10 g (Scophthalmus maximus) (Buck et al.
2012). This fish size of the “model organism” would in terms of scaling correspond
to a market sized adult turbot, which would be farmed in real offshore cages.
After acclimatizing the fish in the cage model after several hours the pump was
switched on for a short term to induce a current velocity of 0.9 ms
-1 at the exhaust
pipe. The pump was adjustable in the tank so that the distance to the cage could be
11 The German Case Study: Pioneer Projects of Aquaculture …
285
Although the oxygen saturation in the German Bight is very high below 10 m
depth, temperatures in extreme years can reach values outside of the physiological
capacity of H. hippoglossus. Furthermore, Atlantic halibut is sensitive to strong
currents and turbidity (Buck et al. 2012). For offshore site selection, it is important
to identify an area with a sufficient supply of oxygen, a moderate temperature
regime as well as low current flow and turbidity.
11.3.4.4 Candidate: Scophthalmus maximus
The turbot is one of the most valuable food fish of the North-East Atlantic. Since
the 1990s, intensive production methods are established for all stages of life of this
species (Moksness et al. 2004). Today, the on-growing of turbot takes place mainly
in land-based recirculating aquaculture systems. S. maximus can be held in very
high stocking densities at optimum parameters (Daniels and Watanabe 2010). The
culture in surface cages, or submersible cages, was successfully demonstrated at
moderate velocities and a constant temperature regime (Daniels and Watanabe
2010). Since the growth of turbot rapidly decreases below 14 °C and above 20 °C
and it stops feeding below 8 °C and above 22 °C, the temperature conditions in the
German-Bight do not favour on-growing year-round (Person-Le Ruyet et al. 2006;
Daniels and Watanabe 2010). In addition, this species is sensitive to the tide flow
rates of up to 1.2 ms
−1 (Buck 2002), which plays an important role for site selection
in the German Bight (Buck et al. 2012).
Taking the results of current velocities and waves on cages and the nets (see
Sect. 11.4 “Technologies” below) into account a further test was conducted to proof
the behaviour of the culture candidates living in these high energy environments.
These tests were conducted at the ZAF (Zentrum für Aquakulturforschung/Center
for Aquaculture Research) under the umbrella of the AWI. A cage prototype
(Fig. 11.18b, c) was manufactured and installed in a large raceway of a RAS
(Recirculating Aquaculture System) including a water treatment device (drum filter,
nitrifying and denitrifying filter, and protein skimmer) to guarantee best water
quality during the experiment. This cylindrical cage (see section above) was
mounted in a way that an adjustable pump (Hydor Koralia magnum 5, flow rate
6,500 l/h) induced a certain current velocity on the cage and its inner culture space.
The cylinder cage in a size of 1:40 was taken from the current flume/wave tank
investigations in Hanover.
The challenge in the subproject of Project No. 13 “Open Ocean Multi-Use” was
to find fish species in small size to be used as model organism, such as juvenile
turbots with a mean size of approx. 10 g (Scophthalmus maximus) (Buck et al.
2012). This fish size of the “model organism” would in terms of scaling correspond
to a market sized adult turbot, which would be farmed in real offshore cages.
After acclimatizing the fish in the cage model after several hours the pump was
switched on for a short term to induce a current velocity of 0.9 ms
-1 at the exhaust
pipe. The pump was adjustable in the tank so that the distance to the cage could be
11 The German Case Study: Pioneer Projects of Aquaculture …
285