Brankica Djordjevic defended her PhD thesis on December 15th 2009

Ane Gro Siri Skjelfjord

Physiological and genomic responses in salmonids with special emphasis on welfare and novel feed ingredients

There is a lack of research techniques that comply with welfare issues and allow long-term physiological and transcriptome monitoring in live fish. The aim of this work was to validate cannulation techniques and global gene expression analysis to be utilized as a standard tool in nutrition and welfare based studies in salmonid fish (Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss)).

Blood vessel cannulation enables repeated blood sampling from the same free swimming individuals; it reduces the required number of fish and also the statistical effect of variation between individuals. The recovery pattern after application of either dorsal aorta (DA) or hepatic portal vein (HPV) cannulation techniques was evaluated in Atlantic salmon. Both methods involve several procedures that are known to stress the fish, such as handling, sedation and surgery, in addition to isolating the fish in individual tanks. The recovery was assessed by measuring changes in circulating plasma cortisol, blood pH, haematocrit (Hct), partial pressures of carbon dioxide (pCO2), electrolytes (Na+, K+, Cl-) and glucose in whole blood. The results confirmed a relatively fast recovery pattern, within 24-72 hours (h), of all variables, after implanting the cannulae.

Thereafter, dual cannulation (HPV and DA) was performed in rainbow trout, following the hypothesis that lipids could undergo hepatic modification immediately after absorption and transport by the HPV. Two experimental diets were also compared one of which contained substitution of fish meal by corn gluten meal and the other contained only fish meal. Lipid content, free fatty acids (FFAs) profiles and relative lipid class composition did not show any significant difference between DA and HPV at any postprandial time. Only few plasma FFAs were affected by different diets but did not differ between DA and HPV. These results demonstrated that in rainbow trout, postprandial uptake and modification of lipid classes and FFAs was different compared to amino acids. No significant differences between HPV and DA lipid levels raised following hypotheses: 1) circulating lipid levels and composition are tightly controlled by regulating the uptake or release of lipids from adipose and hepatic tissue in order to balance the absorption from a meal; 2) the secondary system/lymphatics has a role in lipid uptake and transport; 3) the lipid absorption and metabolism in rainbow trout is too slow and therefore the plasma reflects a steady state.

Furthermore, the differences in postprandial plasma lipid content, FFAs and free amino acids (FAAs) profiles in fish fed diets with proteins of different origin in either DA-cannulated repeatedly sampled or in uncannulated terminally sampled Atlantic salmon were investigated. No lipid postprandial alterations in DA-cannulated fish were tracked, which indicated that cannulation might not be the tool of choice to follow postprandial changes of lipids unless combined with radioactive tracers. On the other hand, FAAs postprandial changes followed in DA-cannulated fish provided more information on the dynamics of nutrients' uptake compared to limited data from terminally sampled uncannulated fish. In DA, the maximum postprandial concentration peak of essential AAs (EAAs) was detected later than for non-essential AAs (NEAAs) (6 vs 3 h, respectively). The individual EAAs showed a similar postprandial pattern; however, the different diets resulted in different starting values, kinetics of absorption and level of maximum concentration after feeding.

Finally, global gene expression analyses were used to assess the immunostimulant candidate lentinan, a beta-glucan from the mushroom Lentinula edodes. Rainbow trout, fed with lentinan-supplemented (L) and control (C) diets were injected with bacterial lipopolysaccharide (LPS), an inflammation inducing agent. Genomic tools used here (salmonid 1.8 k cDNA microarray in combination with the real-time qPCR) permitted the identification of differentially regulated splenic molecular pathways in L and C. Results from this study suggested that lentinan prevented acute and potentially dangerous effects of LPS but did not suppress inflammatory responses in general. Lentinan decreased the expression of genes involved in leukocyte recruitment. In addition, it lowered the expression of IFN-related and TNF-dependent genes and genes involved in MHC class I antigen presentation.

Updated: 23.12.09
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