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Nr. 1 / 2006

Norwegian aquaculture regulations state that fish breeding shall stress the importance of generating a healthy and robust fish. Reducing loss and mortality is economically important for the fish farmer and is equally important from an animal welfare perspective. The salmon’s story as a domestic animal is short; just a few salmon generations have passed since the progenitors of today’s farmed salmon were collected from the rivers. During this short space of time production intensity in the salmon industry has increased considerably, which demands an increased ability of the salmon to adapt.

Resistance to specific infectious diseases and deformities

Aqua Gen is already selecting for a more healthy and robust fish. This selection comprises, for example, an increased resistance to the infectious diseases IPN, furunculosis and ISA and a reduction in the incidence of deformities. Other diseases are also considered for inclusion in the breeding goal. Even though diseases and deformities are important loss factors, larger scale losses with unclear causal connections are also recorded. New traits in the breeding goal should meet a set of criteria:

• Genetic variation of the trait
• Importance for the industry in terms of economy and production management
• The trait should be recorded/ tested on a high number of fish at affordable costs

The heart- and circulatory system

Heart ailments represent one of several production diseases in fish farming, and have during the last years been focused on by the salmon industry, aquaculture scientists and health personnel (Tørud et al., 2004). Knowledge of the prevalence of pathological changes in the heart- and circulatory system and its impact on Norwegian fish farming has been collected. There are strong indications that heart- and circulatory diseases play an important role in non-specific mortalities in fish farms. In livestock species, like chicken, pig and cattle, negative effects of high production intensity are well documented (Rauw, 1998). In chicken the prevalence of respiratory and circulatory diseases has increased in step with increased growth rate and meat yield. In chicken breeding, heart and lung capacity has therefore been included as a selection trait. Aqua Gen wanted to evaluate the possibility of including a similar selection trait in salmon breeding.

Testing of swimming performance as a measure for the function of the heart and circulatory system

Testing of swimming capacity in fish to examine the effects of various environmental factors is a well-established method. Claireaux et al. (2005) reported from a study on rainbow trout that poor swimmers had significantly more rounded heart ventricles (reduced ventricle length to height ratio) compared with good swimmers, which in turn was correlated with fish condition factor. They also found clear indications that maximum heart capacity was correlated with metabolic rate and maximum swimming speed. This study is very interesting, because the results indicate that a swimming performance test can discriminate between individuals with good and poor circulatory capacity. Aqua Gen has performed preliminary stress/strain tests making it possible to distinguish between fish with various relative heart size/shape and have confirmed that this variation is controlled by genetic components (unpublished data).

New research project

Based on knowledge from previous studies Aqua Gen wanted to investigate if swimming performance can be used to distinguish between fish with good and poor heart function. The project: Swimming performance in farmed salmon: a measure for heart-/circulatory function and morphology for genetic selection for a more robust salmon. The project is partly funded by the Norwegian Research Council and started 1 January 2006. Another participant in the project is The Norwegian Institute for Water Research (NIVA), who has constructed a chamber for testing the swimming performance. The Norwegian School of Veterinary Science is responsible for the pathological aspects of the project, which also includes ultrasound scanning of live fish. Brit Tørud, Fiskehelsa BA, is also participating in the project.

In March 2006, 3000 fish from 200 families were tested in the swimming chamber. Genetic variation between families was detected. The fish have been transferred to sea net pens and will be examined alive with ultrasound imaging, following this, pathological examination of the heart will be done at slaughter. This will make it possible to find if swimming performance is correlated with "health criteria" recorded by means of various heart examinations. If such correlations are demonstrated, the specially constructed "thread mill" can then be used for selection of the fish with the best heart- and circulatory system. This will make it possible for Aqua Gen to expand the range of criteria used for selecting a more robust farmed salmon.

Figure 1. The special constructed “treadmill” for fish. The swim capacity is being tested when the fish is exposed to a gradually stronger water flow. Fish not managing the strong current ends up in the light area and is finally caught on the grate. 

References

Claireaux,G., McKenzie,D.J., Genge, A. G., Chatelier, A., Aubin, J. and Farell, A. P. Linking swimming performance, cardiac pumping ability and cardiac anatomy in rainbow trout. J. Exp. Biol. (2005) 208: 1775-1784.

Rauw, W. M., E. Kanis, E.N. Noordhuizen-Stassen & F.J. Grommers, 1998. Undesirable side effects of selection for high production efficiency in farm animals: a review. Livestock Production Science 56: 15-33

Tørud, B. og Hillestad, M. (red.) (2004) "Hjerterapporten". Rapport om hjertelidelser hos laks og regnbueørret. http://www.fiskerifond.no/files/projects/attach/ hjerterapporten.pdf

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