VACCINATION INDUCED REDUCTION IN GROWTH RATE IN SALMON IS NOT MEDIATED THROUGH INCREASED METABOLIC COSTS OR REDUCED METABOLIC SCOPE
Introduction
Reduced appetite/feed intake in the first period after vaccination is a common observation in Atlantic salmon smolt production (Midtlyng et al. 1996; Sørum and Damsgård, 2004; Berg et al. 2006). The reduction in growth is mainly caused by the vaccine itself and not by the anaestetisation and handling (Sørum and Damsgård, 2004) and e.g. Grini et al. (2011) quantified the effect to 0.2% (SGR) during 6 weeks following vaccination at 16 oC and 90-100% DO. The difference between the oxygen consumption rate of a starved and resting fish and the oxygen consumption rate of a maximally active fish is termed the aerobic metabolic scope and is a measure of the capacity for all 'voluntary' activity (e.g. feed intake, digestion and with reference to this project the physiological and immunological response to vaccination). Assimilated oxygen must be partitioned between (among several things) feed intake and growth and a possibly oxygen demanding immune response. An oxygen and energy demanding immune response after vaccination will reduce available oxygen and energy for feeding and growth, as well as reduce the proportion of ingested energy that can be used for growth because of increased metabolic costs of maintenance and activity. We have tested whether vaccination increases the oxygen consumption rate of Atlantic salmon and whether this can explain observations of reduced feed intake and growth after vaccination.
Materials and methods
Unvaccinated Atlantic salmon parr (Salmo salar L.) from the Aquagen strain were transferred to 16 tanks (475L) with approximately 5 kg/tank (fish weight 104-122g) on 9 December 2016. After transfer the temperature was increased with 1 C/day (from 6 oC to12 oC) and for three weeks the fish were trained to a feeding regime of one daily meal (surplus, 2 hours from 1200). After this training period the fish in 8 of the tanks were vaccinated (intra peritoneal injection according to SPC, Aquavac PD7) and the fish in the other 8 tanks sham injected (sterile saline) on the 2nd of January. The fish were starved on the day of vaccination and until the first day after vaccination. The fish were weighed in bulk at the start of the experiment, at vaccination and at termination (22nd of January). Flow through rate in the tanks was 12 l/min, keeping the DO within the range 80-95%. The tanks were continuously illuminated. Oxygen consumption rate was estimated using the tanks as open respirometers, using continuous oxygen readings from the outlets of the tanks.
Results and discussion
Over the 3 weeks following vaccination, average daily growth rate was 2.7 times higher in the sham fish than in the vaccinated fish (1.00 vs. 0.37 percent per day). The oxygen consumption rates over the course of the experiment is shown in Figure 1. Before the day of vaccination, all tanks displayed similar diel patterns in oxygen consumption rate, with a pronounced increase, about 100%, at the onset of feeding, and then a gradual decrease as feeding activity and SDA declined until the feeding session the next day. On the day following vaccination, no food was offered. Both groups then had very similar and stable oxygen consumption rates, reflecting no differences in routine metabolic rates and the absence of feeding activity and SDA of the non-fed fish. As the fish were again offered feed, the pattern from before vaccination was fully reestablished in all sham groups, but much less in the vaccinated groups. The first 10 days the vaccinated fish had a very small VO2 increase during feeding. Thereafter VO2 increase during feeding gradually approached that of the sham fish.
In conclusion, the vaccine did not cause any increase in routine metabolic rate, so arguably the vaccinated fish did not have a reduced aerobic metabolic scope: The hypothesis that reduced appetite and growth of vaccinated fish is a result of compromised metabolic scope was not supported. The vaccinated fish did not have higher routine metabolic costs. The hypothesis that reduced growth of vaccinated fish is a result higher metabolic costs was not supported. The reduced appetite and growth after vaccination is mediated through a different pathway than available aerobic capacity and metabolic costs.
Acknowledgement
This study was sponsored by MSD Animal Health Norge AS
References
Berg A, Rødseth OM, Tangerås A, Hansen TJ. 2006. Time of vaccination influences development of adherences, growth and spinal deformities in Atlantic salmon (Salmo salar L.). Dis. Aquat. Org. 69: 239-248.
Grini, A., Hansen, T., Berg, A., Wargelius, A, Fjelldal PG. 2011. The effect of water temperature on vertebral deformities and vaccine-induced abdominal lesions in Atlantic salmon, Salmo salar L. J. Fish Dis. 34, 531-546.
Midtlyng, PJ., Reitan, LJ., Speilberg, L. 1996. Experimental studies on the efficacy ad side-effects of intraperitoneal vaccination of Atlantic salmon (Salmo salar L.) against furunculosis. Fish Shellfish Immunol. 6, 335-350.
Sørum, U., Damsgård, B. 2004 Effects of anaesthetization and vaccination on feed intake and growth in Atlantic salmon (Salmo salar L.). Aquaculture 232, 333-341.
