Impaired compensatory growth following disease exposure in fasting herring

We examined effects of winter fasting and disease exposure on energetics of juvenile Pacific herring in a laboratory. Juvenile herring utilize most on-board energy stores over winter when prey availability is low, putting them in an energetically-sensitive condition in spring. In this low-energy state, juvenile herring may be most susceptible to disease, which is thought to play a part in struggling herring populations. We fasted juvenile herring to simulate winter fasting conditions and exposed them to Icthyophonus hoferi, a highly pathogenic parasite which is ubiquitous in herring populations throughout the NE Pacific. Following exposure, herring were placed in three temperatures and refed to simulate spring feeding conditions. We sampled herring at two intervals over the following two months to examine the energetic toll of Icthyophonus infection. All fasted herring demonstrated a compensatory response in total energy content within a month of re-feeding. Infected herring had an impaired compensatory response, however, that was 20% less than their uninfected counterparts. After one month , infected fish had 7.2% less energy than uninfected fish, which increased to 15% after two months. Impaired energy accumulation resulted in failure to attain lipid stores. We suspect energy was being diverted from storage to contend with infection.