within a range of 25–150 cm. This distance to the cage and the resulting current
velocity was calculated by using a corresponding situation as it occurs at the
offshore site. After starting the experiment fish behaviour, escape response, welfare,
and reaction at feeding were recorded using an underwater video camera.
The results of these investigations show a strong impact of strong current
velocities on farmed turbot within the cage. Juvenile turbot are unharmed at
velocities of 0–1.0 ms
-1
. However, the fish are affected by stronger currents in a
way that the fish will be transferred from their resting area on the bottom of the cage
resulting in more activity of the fish swimming against the current trying to resettle
on the bottom. At very strong current velocities of 1.5 ms
-1 and higher it might
happen that young turbots are pressed against the net of the cage leading to the risk
to obtain skin injuries.
To summarize, these results show that turbot cultivation offshore is not suitable
if current velocities exceed a certain value, making a site-selection-criteria process
necessary. However, we have to take into account that we used small fish—the
model organism—in the experiment, which allowed the upscaling to a size corresponding with real fish sizes to be farmed at offshore sites. As fish in a size we used
in this investigation will never be transferred to offshore sites as it is described in
this book we assume that larger fish, which normally will be cultured in offshore
cages, will act differently.
11.3.4.5 Candidate: Melanogrammus aeglefinus
The haddock is a valued food fish on both sides of the North Atlantic, but its wild
catches stagnate, so that haddock is an interesting candidate for aquaculture
(Moksness et al. 2004). In recent years, the cooperation of a large commercial
salmon production (Heritage Salmon Limited) with various Canadian research
institutes lead to great advances in the management of broodstock, the feed of
larvae, as well as the weaning and on-growing methods (Chambers and Howell
2006). Same as cod, haddock is a physoclist species and breaks in descents and
ascents need to be included to prevent barotraumas due to rapid pressure changes
by vertical movement of the cages. (Buck et al. 2012). Moreover, M. aeglefinus has
the ability to penetrate even tight mesh (Özbilgina and Glass 2004), precaution
needs to be taken to prevent escapes. The on-growing of M. aeglefinus in submersible offshore cages has proven to be very promising, reaching good growth
rates in a 600 m
2 Sea Station at the temperature conditions off the coast of New
Hampshire (Chambers and Howell 2006). However, the similarly high growth rates
as cod in the first year decreased slightly and the growth potential over longer
periods of time must be considered to be lower than in cod (Treasurer et al. 2006).
Haddock can tolerate temperatures between 1 and 20 °C (Chambers and Howell
2006), making it a potential aquaculture species for the offshore area in the German
Bight.
286
B.H. Buck et al.
velocity was calculated by using a corresponding situation as it occurs at the
offshore site. After starting the experiment fish behaviour, escape response, welfare,
and reaction at feeding were recorded using an underwater video camera.
The results of these investigations show a strong impact of strong current
velocities on farmed turbot within the cage. Juvenile turbot are unharmed at
velocities of 0–1.0 ms
-1
. However, the fish are affected by stronger currents in a
way that the fish will be transferred from their resting area on the bottom of the cage
resulting in more activity of the fish swimming against the current trying to resettle
on the bottom. At very strong current velocities of 1.5 ms
-1 and higher it might
happen that young turbots are pressed against the net of the cage leading to the risk
to obtain skin injuries.
To summarize, these results show that turbot cultivation offshore is not suitable
if current velocities exceed a certain value, making a site-selection-criteria process
necessary. However, we have to take into account that we used small fish—the
model organism—in the experiment, which allowed the upscaling to a size corresponding with real fish sizes to be farmed at offshore sites. As fish in a size we used
in this investigation will never be transferred to offshore sites as it is described in
this book we assume that larger fish, which normally will be cultured in offshore
cages, will act differently.
11.3.4.5 Candidate: Melanogrammus aeglefinus
The haddock is a valued food fish on both sides of the North Atlantic, but its wild
catches stagnate, so that haddock is an interesting candidate for aquaculture
(Moksness et al. 2004). In recent years, the cooperation of a large commercial
salmon production (Heritage Salmon Limited) with various Canadian research
institutes lead to great advances in the management of broodstock, the feed of
larvae, as well as the weaning and on-growing methods (Chambers and Howell
2006). Same as cod, haddock is a physoclist species and breaks in descents and
ascents need to be included to prevent barotraumas due to rapid pressure changes
by vertical movement of the cages. (Buck et al. 2012). Moreover, M. aeglefinus has
the ability to penetrate even tight mesh (Özbilgina and Glass 2004), precaution
needs to be taken to prevent escapes. The on-growing of M. aeglefinus in submersible offshore cages has proven to be very promising, reaching good growth
rates in a 600 m
2 Sea Station at the temperature conditions off the coast of New
Hampshire (Chambers and Howell 2006). However, the similarly high growth rates
as cod in the first year decreased slightly and the growth potential over longer
periods of time must be considered to be lower than in cod (Treasurer et al. 2006).
Haddock can tolerate temperatures between 1 and 20 °C (Chambers and Howell
2006), making it a potential aquaculture species for the offshore area in the German
Bight.
286
B.H. Buck et al.