The effect of allostatic load on hypothalamic–pituitary–interrenal (HPI) axis before and after secondary vaccination in Atlantic salmon postsmolts (Salmo salar L.)

Abstract

The experiment consisted of three experimental groups; 1) "vaccine and stress", 2) "stress and vaccine" and 3) control. All groups have previously been vaccinated 6 months prior to the start of the experiment. At the start of the experiment the "vaccine and stress" group was vaccinated with Pentium Forte Plus for the second time (25.02.2008), and then given a daily stressor (crowding stressor, 267 kg m-3 in 15 min) for a period of four weeks. The "stress and vaccine" group was given a similar daily stressor for four weeks, and then vaccinated for the second time. The control group was neither stressed nor vaccinated a second time. The results indicates that a fish in the "stress and vaccine" group enters an allostatic overload type 2 due to oversensitivity to ACTH, a reduced efficient negative feedback system, with elevated baseline levels of plasma cortisol, and reduced immune response with pronounced effects on the wellbeing of the animal. The "vaccine and stress" group entered an allostatic overload type 1 response, with oversensitivity to ACTH and transient reduced efficient negative feedback system, but at the end of the experiment the fish had recovered. This study shows that if plasma cortisol becomes elevated prior to vaccination it could instigate an allostatic overload type 2 with dire consequences on animal welfare. To reduce the risk of compromising the animal welfare during commercial vaccination of salmon one propose to grade the fish minimum a week prior to vaccination, or grade simultaneously with vaccination. This could reduce the overall allostatic load during handling and vaccination, and secure a healthy fish, with intact immune response and improved animal welfare.3

Salinity effects on plasma ion levels, cortisol, and osmolality in Chinook salmon following lethal sampling

“…Stress has been linked to increased plasma Mg 2+ concentration over time in anaesthetized rainbow trout (O. mykiss) when MS-222 was used following a stressor (being lifted out of the water for 20 seconds) (Soivio et al, 1977). Similar link between plasma cortisol and Mg 2+ has also been shown in Atlantic salmon following daily crowding stress for 4 weeks with a subsequent vaccination (Iversen and Eliassen, 2014). Iversen and Eliassen concluded that fish who may have entered an allostatic overload type 2 became oversensitive to ACTH, reducing efficient negative feedback system and elevating base-line level of plasma cortisol.…”

Cohabitation With Atlantic Salmon (Salmo salar) Affects Brain Neuromodulators But Not Welfare Indicators in Lumpfish (Cyclopterus lumpus)

“…In domesticated mammals, an injection of ACTH has shown an increased cortisol response in animals reared in poor conditions or subjected to repeated stressors. Similarly, Iversen and Eliassen (2014) showed that salmon that were stressed daily over a 4-week period became oversensitive to ACTH, regardless of whether the fish were vaccinated before or after applied stressor. One can only speculate how the Model treatment triggered the HPI axis in a single individual.…”

“…To avoid stress during handling, fish were quickly hand netted from the experimental tank to a 30 L tank with 5 mg L –1 of cortisol blocking metomidate (Aquacalm™, Western Chemical Inc, Ferndale, United States). This concentration causes rapid anesthesia and stops further increase of plasma cortisol ( Iversen et al, 2003 ; Iversen and Eliassen, 2014 ). Fish were moved back to their respective tanks after the measurements were done.…”

“…To investigate treatment impact on the HPI-axis feedback system, a stimulation and suppression test using adrenocorticotropic hormone (ACTH) and dexamethasone (DEX), respectively, was conducted in accordance with the previous study by Pottinger and Carrick (2001) , with some minor modifications as described in Iversen and Eliassen (2014) .…”

Ensuring Sustainable Development of Aquaculture by Enhancing the Natural Immunity of Fish

“…Managers have different important points to consider before applying vaccination: biological species characteristics of cultured objects; the real status of the immune system of objects of cultivation; the production cycle and life cycle of the cultivated species on the fish farm; features of the seasonal diseases in a fish hatchery; technology of fish farming processes; abiotic characteristics of the aquatic environment (distribution and fluctuation of temperature, salinity, etc. ); stressing factors; feeding / nutritional characteristics and monetary benefits [7].…”