Torbjørn Einar Åsgård

Determination of digestibility of commercial salmon feeds

The aim of the study was to develop an applicable method for determination of the digestibility of nutrients in commercial feeds. Leaching of markers and dry matter (DM) were compared between a commercial extruded feed containing La 2 O 3 , the same commercial feed coated with oil and other additional markers, and the commercial feed that had been ground and re-pelleted with water, marker and a crude alginate binder. Two markers, Y 2 O 3 and Cr 2 O 3 , were added in both the coated and the moist feeds. The optimal inclusion level of binder and water to minimize the leaching of DM from the moist pellet was determined in a preliminary study. The lowest leaching of DM was achieved with the inclusion of 2% alginate and 35% water. Added markers tended to be less homogeneously included in the coated feed than in the moist feed, and the markers leached relatively more than the DM from the coated feed. Apparent digestibility coefficients (ADCs) of DM, fat, nitrogen (N), energy, organic matter (OM), and phosphorus (P) in the commercial dry feed and the moist feed were compared in two experiments with Atlantic salmon. Differences between the ADCs in the two experiments were observed for N and P. The ADC estimates of the moist feed were slightly lower than those of the dry feed for all nutrients. Similar ADC estimates for each nutrient were obtained for all markers, except for Y 2 O 3 which produced a slightly higher ADC for N than did La 2 O 3 . By using the moist feed method recommended from this study, a difference of about 1.4% units in ADC of energy and of 0.8% units for N between the original and the modified test feed was demonstrated. This means the error of ADC estimates is low compared to using fixed digestibility coefficients for each of protein, fat and carbohydrate, a method that has been employed for declaration of commercial fish feed. Further development of the method is discussed.

Effects of a temperature shift on seawater challenge test performance in Atlantic salmon (Salmo salar) smolt

Abstract Seawater tolerance of Atlantic salmon ( Salmo salar ) smolts acclimated at 8°C in fresh water was tested in seawater challenge tests at 2°C, 5°C, 11°C, 14°C and 17°C, and compared to a test at 8°C. Two tests were used, a 24-h, 35‰ and a 24-h, 40‰ salinity test. In 35‰ salt water, there were no differences in plasma Cl − concentrations in the range 5–14°C (mean values 140–144 mM). An increase in plasma Cl − level was found at 2°C and 17°C (mean values about 155 mM). The mean Cl − concentration at 8°C in 40‰ test was 10 mM higher than that at the same temperature in 35‰ salinity. An increase in plasma Cl − level was found when the temperature shifted from 8°C to either 5°C or 14°C (mean values 171 mM), and an even larger increase was recorded at 2°C (mean value 209 mM, 75% mortality) and 17°C (mean value 194 mM). The results indicated that smolt had the ability to hypoosmoregulate over a wide range of temperatures when transferred to full-strength sea water. However, differences from the acclimation temperature larger than 4–6°C are not recommended, especially when the seawater temperature is lower than in fresh water. The use of a higher salinity than that of full-strength sea water may give a more comprehensive picture of the hypoosmoregulatory ability of smolts, and may possibly be used to distinguish differences in hypoosmoregulatory capacity of smolts not readily obtained from tests in full-strength sea water.

Molecular and physiological responses to long-term sublethal ammonia exposure in Atlantic salmon (Salmo salar)

The objective of this study was to determine the underlying physiological and molecular responses to long-term sublethal ammonia exposure in Atlantic salmon (Salmo salar) parr. Previous studies have predominately focused on mechanisms during acute, short-term exposure. For that purpose Atlantic salmon parr were exposed to four ammonia concentrations between 4 and 1800 μmol l(-1) total ammonia nitrogen (TAN), and subjected to two feeding regimes for 15 weeks. Elevated environmental ammonia and full feeding strength caused an initial increase in plasma ammonia levels ([T(amm)]) after 22 days of exposure, which thereafter declined and remained similar to the control animals towards the end of the study. On the other hand, a progressive decrease in plasma urea levels was evident throughout the entire exposure period and depended on the concentration of environmental ammonia, with the largest decrease in urea levels observed at the highest ammonia concentrations (1700 and 1800 μmol l(-1) TAN). We hypothesized that the successful adaptation to long-term elevated ammonia levels would involve an increased capacity for carrier-facilitated branchial excretion. This hypothesis was strengthened by the first evidence of an up-regulation of branchial transcription of the genes encoding the Rhesus (Rh) glycoproteins, Rhcg1 and Rhcg2, urea transporter (UT) and aquaporin 3a (Aqp3a), during long-term exposure. Of the Rhesus glycoprotein (Rh) mRNAs, Rhcg1 was up-regulated at all tested ammonia levels, while Rhcg2 showed a concentration-sensitive increase. Increased transcription levels of V-type H(+)-ATPase (H(+)-ATPase) were observed at the highest ammonia concentrations (1700 and 1800 μmol l(-1) TAN) and coincided with an up-regulation of Rhcg2 at these concentrations. Transcription of UT and Aqp3a was increased after 15 weeks of exposure to low ammonia levels (470 and 480 μmol l(-1) TAN). A significant increase in brain glutamine (Gln) concentration was observed for full fed Atlantic salmon after 22 days and in fish with restricted feeding after 105 days of exposure to 1800 and 1700 μmol l(-1) TAN, respectively, without any concomitant decrease in brain glutamate (Glu) concentrations. These results suggest that Gln synthesis is an ammonia detoxifying strategy employed in the brain of Atlantic salmon parr during long-term sublethal ammonia exposure. Full feed strength had an additive effect on plasma [T(amm)], while the restricted feeding regime postponed the majority of the observed physiological and molecular responses. In conclusion, Atlantic salmon parr adapts to the long-term sublethal ammonia concentrations with increased branchial transcription levels of ammonia and urea transporting proteins and ammonia detoxification in the brain.

Changes in protein abundance in the vertebral columnof Atlantic salmon (Salmosalar) fed variable dietary P levels

Previously we have applied a comparative 2DE-approach to investigate the proteome of Atlantic salmon (Salmo salar) with vertebral deformities (Pedersen et al., 2011). This work lead to the identification of a new interesting candidate for the process that leads to fused vertebrae; matrilin-1. This finding was further confirmed by real-time PCR analysis and immunohistochemistry, and illustrates the strength of applying a non-hypothetical approach towards identifying new markers for bone development.