Development of the salmon louse Lepeophtheirus salmonis and its effects on juvenile sockeye salmon Oncorhynchus nerka

Abstract

Responses of sockeye salmon Oncorhynchus nerka during infection with Lepeophtheirus salmonis were assessed in controlled laboratory trials. Juvenile salmon were exposed to 100 copepodids fish −1 (Trials 1 and 2) or 300 copepodids fish −1 (Trial 3) at mean weights of approximately 40, 80 and 135 g, respectively. Infections occurred on all salmon in all trials, and mean abundances (infection densities) ranged between 3. At attachment sites on gills, we observed hyperplasia of basal epithelial cells and fusion of secondary lamellae occasionally associated with a cellular infiltrate. At attachment sites on fins, partial to complete skin erosion occurred, with limited evidence of hyperplasia or inflammation. Scale loss and abrasions coincided with pre-adult lice around 20 d post infection (dpi). Plasma osmolality was significantly elevated in exposed fish in Trials 1 (21 dpi), 2 (15 and 36 dpi) and 3 (20 dpi), whereas haematocrit was significantly depressed in exposed fish in Trials 1 (21 and 28 dpi) and 3 (20 dpi). Plasma cortisol was significantly elevated in exposed fish at 20 dpi (Trial 3). Physiological changes and mortality were related to the intensity of infection and became most prominent with pre-adult stages, suggesting patterns of infection and response in sockeye salmon similar to those reported for Atlantic and Chinook salmon.KEY WORDS: Sockeye salmon · Salmon lice · Physiology · Histopathology · Host response · SusceptibilityResale or republication not permitted without written consent of the publisher

Comparative transcriptomics of Atlantic Salmo salar, chum Oncorhynchus keta and pink salmon O. gorbuscha during infections with salmon lice Lepeophtheirus salmonis

“…Here, the consequences of elevated infection densities on chum and Atlantic salmon were reflected in elevated plasma cortisol (chum), reduced weight gain (chum), and reduced hematocrit (chum and Atlantic). Hematocrit reduction in exposed chum and Atlantic salmon and no significant effect in pink salmon confirms previous observations in these species, and this reduction was also noted in sea trout S. trutta , and in sockeye salmon O. nerka infected by lice [4, 22, 48, 49]. In these studies, the reduced hematocrit was related to infection intensity and possibly indicative of a microcytic anemia induced by lesions in the skin caused by feeding parasites, leading to fluid loss.…”

Sea lice, sockeye salmon, and foraging competition: lousy fish are lousy competitors

“…However, it is not known how or whether parasite exposure fits into the long-term decline of sockeye productivity. Direct mortality of juvenile sockeye from C. clemensi infection has not been estimated, but it is likely very low; in a laboratory setting, L. salmonis infection does not cause direct mortality except at extreme abundances not seen in wild fish (Jakob et al 2013). Because Pacific salmon experience high mortality during their early marine life (Bax 1983;Parker 1968) and early marine growth is crucial for survival (Beamish et al 2004;Farley et al 2007;Moss et al 2005), any impact of C. clemensi on sockeye population dynamics is probably indirect, by modulating competition or predation.…”

“…These high mortality rates of fish in the absence of pathogens make it difficult to understand the implications of pathogen infection on fish populations. Consequently, studies restricted to direct effects on survival or physiology (e.g., Jakob et al 2013) are only tangentially relevant for fish populations because they ignore how pathogens interact with other processes that can lead to high mortality, such as competition and predation.…”

Reduced growth in wild juvenile sockeye salmon Oncorhynchus nerka infected with sea lice

“…While direct mortality from sea lice is probably very low for O . nerka (Jakob et al ., ), the indirect effects of louse parasitism on these fish are unknown apart from an association with reduced competitive ability in highly infected fish (Godwin et al ., ). Oncorhynchus nerka are of particular interest because of their iconic status, their importance to fisheries (FAO, ), and their complex multi‐host dynamics with sea lice; C .…”