Atlantic salmon smolt. (Photo: UMB, Knut Werner Alsen/Nofima)
Smolt become more robust through exercise
Tuesday, July 24, 2012, 22:40 (GMT + 9)
Farmed salmon smolts become more robust and more likely to survive if they undergo optimal aerobic exercise training prior to sea transfer.
Robust smolts have improved disease resistance associated with a strengthened cardiovascular system and better growth.
Start while they are young
Vicente Castro and his colleagues at Nofima Mat, the Norwegian Institute of Food, Fisheries and Aquaculture Research, measured the extent to which these parameters were improved by different physical training regimes in salmon juveniles (pre-smolts) in fresh water, thereby improving smolt robustness.
Overall, his work demonstrates that by subjecting pre-smolts to physical exercise, there is a strong potential for the aquaculture industry to produce more robust smolts.
This can in turn result in lower mortalities caused by infectious diseases. Production losses are particularly high the first months after sea transfer, so preventive health measures must be initiated in juvenile fish during the freshwater stage.
As salmon swim constantly, aerobic exercise training is achieved by changing the water velocity and flow conditions in the tanks so that the fish are motivated to swim in a controlled way and at higher speeds than normal over time.
In the trials at Nofima, several different training regimes with intervals and continuous flow were tested.
Greatest benefit for poor swimmers
In one trial, Castro split the salmon population into two groups: good and poor swimmers. Interestingly, the fish that were categorized as good swimmers had an overall higher disease resistance than poor swimmers on a controlled infectious pancreatic necrosis (IPN) challenge test.
After undergoing the physical training programmes, the largest effect on disease resistance was recorded in the group of poor swimmers, with two outcomes.
Their performance was either improved through an optimal regime (achieving similar resistance level as good swimmers), or worsened through a non-optimal regime. This suggests that poor swimmers have lower capability to adapt than good swimmers.
The range of swimming velocity that appears to be optimal for improving overall robustness has been narrowed down by Castro and the research group. While it was earlier thought that 0.5-1.5 body lengths per second was optimal, they now have data that shows that 0.8 – 1.2 body lengths per second is optimal when including improved disease resistance.
“In conclusion, aerobic exercise is good for all salmon but the weakest 50 per cent of the fish may have the greatest benefit from swimming activity,” says Castro.
Physical exercise improved the growth rate, mainly because of an increased feed intake, meaning that fish will reach a given size faster when undergoing training programmes than if they are not subjected to such programmes.
Why training is good
Studies showed that favorable physical training reduced inflammation levels in the heart and the innate immune system was strengthened through activation of several responses. Furthermore, results suggested that physical exercise had a strong effect on enhancing the cardiovascular capacity of the fish, an important factor in achieving high levels of robustness.
“In future research, we need to further optimize the physical training regimes, so we can implement protocols with the potential of large benefits for the fish, the industry and the consumers,” Castro emphasizes.
Possible utilization of this knowledge may also include improving the genetic material in breeding programmes by sorting fish based on swimming performance.
By Reidun Lilleholt/Nofima