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Effects of low to very high water velocities on Atlantic salmon post-smolts: Part I: Growth, muscle development and schooling

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Kjetil Aune

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kjetil.aune@nofima.no

8th International Symposium on Aquatic Animal Health; , 2018-09-02–2018-09-06

Gerrit, Timmerhaus; Timmerhaus, Gerrit; Lazado, Carlo C.; Nikko Alvin, Cabillon; Britt-Kristin, Reiten; Lill-Heidi, Johansen

Beneficial effects of induced water velocities on Atlantic salmon smolts have been described in several studies. These effects include elevated growth rates, feed conversion rates and disease resistance. However, the optimum water velocity for farmed salmon smolts remains unknown. Thus, in this study, we addressed the effects of different water velocities on growth and muscle development (histology and gene markers) to estimate optimum conditions for rearing of post smolts in a recirculating aquaculture system. In addition to individual parameters, we addressed the behavioral response in regards to schooling. We divided 2400 salmon smolts (average start weight 80g) into twelve tanks (200 fish per tank) and set the water velocities for four triplicate tanks to low – 0.5 body length per second (BL/s); medium – 1.0 BL/s; high – 1.8 BL/s; and very high – 2.5 (BL/s). The velocity for the very high group was the highest tested for salmon smolts to date. The trial lasted three months and organ samples were collected at three time points. Time-laps cameras were used to observe the schooling behavior in increasing water velocities and showed that fish in the low and medium group distributed mostly evenly in the tanks. In contrast, fish in high and very high displayed strong schooling behavior at certain spots in the tanks. We observed a close to linear relationship between water velocity and growth rate, which resulted in 5.4% higher average body weight in the very high group than the low group at the end of the trial. The condition factors of fish from the low group was lower than in the other groups and an analysis of the contour of the fish bodies showed that fish in higher velocities grew wider (distance between back and belly outlines). Histological analyses of the muscle fibers revealed increased somatic growth in high and very high groups, while the expression of some genes of myosomatic growth pathways were increased in the same fish. In conclusion, the increased body weight of fish reared in high water velocities was likely due to enhanced somatic growth of muscle fibers. Thus, these findings provide further evidence that elevated water velocities have positive effects on the growth rate of smolts even at the highest levels tested to date.