Náttúra og náttúrutilfeingi
The fatty acid TTA in a dynamic production of Atlantic Salmon (Salmo salar)
1.8.2009 - 31.12.2017
Stuðul úr Granskingargrunninum:
Nofima Marin gjennomfører et strategisk instituttprogram med tittel OPTIPROD i perioden 2007-2010. Dette er et grunnleggende prosjekt der målsetningen er å bidra med ny og integrert forståelse av vekst hos oppdrettslaks, og kunnskap om hvorledes en dynamisk sammensetning av fôret kan tilpasses ulike fysiologiske og miljømessige forhold for å sikre en optimal og stabil produksjon. Internasjonal samarbeidspartner er IFREMER i Frankrike. Regin Arge har deltatt på dette prosjektet som forsker III siden 2008, men er nå flyttet til Færøyene.
I PhD-arbeidet er det planlagt at Regin Arge vil studere den bioaktive fettsyren TTA (tertradecylacetic acid) som fôrtilsetning til atlantisk laks.
Følgende arbeider er planlagt:
-Bearbeide et dose-respons forsøk.
-Studere om økt energiomsetning hos laks om våren (forårsaket av TTA i fôret) reduserer frekvens tidlig kjønnsmodne 0+ hanner påfølgende høst.
-Studere effekten av TTA på peroksisomal betaoksydasjon og fettsyremetabolisme i hjertet.
-Gjennomføre og modellere utvasking av TTA fra muskel og hjerte.
Forsøk og uttak blir utført på Nofima Marin sin forsøksstasjon på Averøy. Laboratorie-arbeidet vil hovedsakelig bli utført utført på Ås (Nofima Marin).
The project began in 2009. From the employer (Fiskaaling) the student was allocated 1/3 of working hours to the project. This meant that most work was done off-hours/weekends/holidays. In 2016, however, 6 months were used for the project incl. experiments/analyses. 2017 was used for writing while in new working position at new employer (Marine Harvest), but again mostly done off-hours. Thesis was submitted in March 2018 and defence done in May 2018.
Utilisation of fatty acids highly dominates energy metabolism in high performance fish as the Atlantic salmon. It is well established knowledge that feed intake and growth of salmon is highly influenced by water temperature and day length. Another significant factor influencing growth and fat deposition in Atlantic salmon, is the initiation of puberty and the development in sexual maturation. Previous research has shown that maturation in salmon is a complex process depending on different stimuli gained from both external factors like photoperiod and internal factors like age and state of energy reserves. After the maturation process has been initiated during early winter, it has been shown that the availability of appropriate energy reserves during the spring period is a major factor affecting continuance of the maturation process, and low energy or fat levels may arrest further progress. Female salmon are known to invest more energy in the development of gonads than male salmon, hence, females normally mature later in life than males, most often in the autumn after two or more sea winters. The combination of these factors significantly influences the production biology of farmed Atlantic salmon and is the scope of this thesis.
In this thesis tetradecylthioacetic acid (TTA) is strategically used in the test diet to alter the fat accumulation in farmed S0 Atlantic salmon muscle during their first spring at sea (paper I). It is shown that lower fat accumulation in spring leads to reduced incidence of early maturation in male grilse in the succeeding autumn by 1/3 compared to the control group receiving the same feed without TTA supplementation. To describe the decrease of TTA in fish muscle after termination of TTA supplementation in the feed, an elimination model is further developed in this study (paper I). As salmon females normally mature at later life stage compared to males, another experiment with S1 salmon was conducted to investigate possible different responses between the sexes regarding TTA treatments (paper II). It is shown that muscle fat in males and females differed significantly as a response to dietary TTA. The muscle fat content during the first spring was significantly lower in females compared to males. In contrast, during the second spring, fat content was significantly more reduced in males than in females. Condition factor is shown to follow a similar pattern as muscle fat. The results in paper II indicate that the difference in male and female fat accumulation dynamics is related to sex-specific reproduction biology of Atlantic salmon.
To obtain more insight into the response to TTA treatments, a study of the salmon heart was selected due to its characteristics as a highly energy consuming vital organ (paper III). It is shown that fish given TTA supplemented feed had a smaller decrease in heart weight relative to fish bodyweight (CSI) in a period after sea transfer compared to the control. This coincided with lowered condition factor and muscle fat in the treated fish. To examine this further, isolated salmon heart cells were held in culture and pre-stimulated with TTA in order to increase the endogenous concentration of this bioactive component. Radiolabelled fatty acid (FA) was supplemented to culture media to study the effects of endogenous TTA on uptake, incorporation in lipid classes and β-oxidation. It is shown that heart cells receiving 120µM TTA had higher uptake of radiolabelled FA and formation of the β-oxidation products CO2 and other acid-soluble products. The molecular mechanisms underlying this were studied in an additional experiment. Salmon held in tanks on land were subjected to injections of TTA in increasing doses. By using gene expression (real-time quantitative RT-PCR) analyses, it is shown that genes regulating cell growth, peroxisomal FA oxidation, FA elongation and desaturation, were upregulated in the heart of TTA treated fish. In contrast, genes involved in FA transport into the mitochondria were not influenced. Taken together, the findings in paper III show that TTA treatments lead to increased heart size, possibly by increasing the expression of genes regulating heart cell growth and enhanced energy production by stimulation of FA oxidation.
In conclusion, the findings in this thesis demonstrate that TTA in defined doses, without compromising fish growth, may successfully be used strategically during energy demanding periods for the fish. Additionally, TTA reduces incidence of early sexual maturation, increases cardiac robustness and oxidative capacity in farmed salmon. Further, the effect of TTA may be influenced by the sex and size of the fish.
Implementation of the knowledge generated by the work in this thesis has the potential of being beneficial for the salmon farming industry.
Scientific articles, books, thesis etc.
Paper I. Arge, R., Thomassen, M.S., Berge, R.K., Zambonino-Infante, J.L., Terjesen, B.F., Oehme, M. and Rørvik, K-A. (2012). Reduction of early sexual maturation in male S0 Atlantic salmon (Salmo salar L.) by dietary supplementation of tetradecylthioacetic acid (TTA). Aquaculture Research 45, 1–12, DOI:10.1111/are.12036.
Paper II. Dessen, J-E., Arge, R., Thomassen, M. S. and Rørvik, K-A. (2016). Differences in fat accumulation between immature male and female Atlantic salmon Salmo salar after dietary administration of tetradecylthioacetic acid. Journal of Fish Biology 89, 2085–2097. doi:10.1111/jfb.13113
Paper III. Arge, R., Dessen, J-E., Østbye, T-K., Ruyter, B., Thomassen, M.S., Rørvik, K-A (2017). Effects of tetradecylthioacetic acid (TTA) treatment on lipid metabolism in salmon hearts – in vitro and in vivo studies. Journal of Fish Physiology and Biochemistry, https://doi.org/10.1007/s10695-018-0466-4
Ph.d.ritgerð varð vard 4. mai 2018.
Heitið á ritgerðini er: “Tetradecylthioacetic acid (TTA) – A functional feed ingredient for Atlantic salmon affecting early sexual maturation, cardiac robustness and β-oxidative capacity”. Norwegian University of Life Sciences 2018, ISSN 1894-6402, ISBN 978-82-575-1508-9
Storage and access rights til collected data: Nofima AS Postboks 210, NO-1431 Ås Osloveien 1, NO-1433 Ås