Henriette Alne defended her PhD thesis on May 28th 2010

Ane Gro Siri Skjelfjord

Tetradecylthioacetic acid (TTA) - A functional feed ingredient for Atlantic salmon (Salmo salar L.): Growth, sexual maturation and health

Farmed Atlantic salmon (Salmo salar L.) is transferred to sea at different times during the year. Independently of time after sea transfer, the salmon experience a period of low performance, characterized by reduced appetite, feed efficiency, growth rate, condition factor, muscle fat and fat retention during first spring in sea (Paper I). In addition, such low-performing periods may be a predisposing factor for outbreak of diseases, such as infectious pancreatic necrosis (IPN) (Paper III) and heart and skeletal muscle inflammation (HSMI) (Paper IV). The temporary reduction in muscle fat content observed during first spring in sea may indicate a higher demand for available energy than what is obtained from traditional salmon feed. In the present thesis tetradecylthioacetic acid (TTA) is used in both 1+ and 0+ farmed Atlantic salmon, during first spring in sea, to enhance muscle fatty acid oxidation capacity. In contrast to previous studies with TTA in fish feed, the idea with the present work was to use diets supplemented with a low level of TTA and only during short periods, where more energy might be needed.

Dietary supplementation of TTA significantly reduced the frequency of sexual mature 1+ male Atlantic salmon first autumn in sea (Paper II). Compared to control, dietary supplementation of TTA resulted in a three-fold reduction in incidence of sexual mature males (0.6% versus 1.8%). The final body weight was not affected. As muscle fat was reduced by dietary TTA in spring, the effect on maturation is probably a consequence of lower energy status at this time, too low to initiate the maturation process.

In 1+ smolt transferred to sea in spring, a natural outbreak of IPN occurred eight weeks after sea transfer. Relative percent survival for the fish fed TTA in sea water was 70% compared with the un-supplemented groups, significantly reducing mortality from 7.8% to 2.3% (Paper III). Plasma chloride was reduced by dietary TTA and related to increased IPN survival, which may suggest an improved osmoregulatory capacity in fish fed a TTA-supplemented diet. Reduced fat and enhanced beta oxidation rate were further observed in white muscle following administration of TTA, indicating that TTA resulted in a re-allocation of dietary fatty acids from storage to energy producing oxidation. In addition to the effect on survival during the IPN outbreak, TTA was found to significantly reduce mortality during a natural outbreak of HSMI in 0+ smolt. The mortality was reduced from 4.7% in the un-supplemented to 2.5% in the TTA-supplemented groups (PaperIV). Expression of several genes related to lipid metabolism (Peroxisome proliferator activated receptor (PPAR) alfa and beta, carnitine palmitoyl transferase I (CPT K) and acyl-CoA oxidase (ACO)) were higher in ventricles from salmon fed TTA. At the same time, urea content in plasma was found to be lower in fish fed TTA. Taken together, these results indicate that the dietary effect on survival may partly be due to an altered metabolic balance, with better protein conservation due to increased lipid oxidation. In addition, 0+ salmon previously fed a TTA-supplemented diet had a higher growth rate during the disease period, compared to the control.

In conclusion, TTA reveals a range of biological and physiological effects in salmon, resulting in better resistance to diseases such as IPN and HSMI, reduced sexual maturation and similar or better growth performance. The presented thesis may exemplify the importance of developing functional feed ingredients in modern fish farming for achieving better growth, reduced sexual maturation and improved health.

Updated: 11.06.10
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