Infections by Renibacterium salmoninarum and Nanophyetus salmincola Chapin are associated with reduced growth of juvenile Chinook salmon, Oncorhynchus tshawytscha (Walbaum), in the Northeast Pacific Ocean

Abstract

We examined 1454 juvenile Chinook salmon, Oncorhynchus tshawytscha (Walbaum), captured in nearshore waters off the coasts of Washington and Oregon (USA) from 1999 to 2004 for infection by Renibacterium salmoninarum, Nanophyetus salmincola Chapin and skin metacercariae. The prevalence and intensities for each of these infections were established for both yearling and subyearling Chinook salmon. Two metrics of salmon growth, weight residuals and plasma levels of insulin-like growth factor-1, were determined for salmon infected with these pathogens/parasites, both individually and in combination, with uninfected fish used for comparison. Yearling Chinook salmon infected with R. salmoninarum had significantly reduced weight residuals. Chinook salmon infected with skin metacercariae alone did not have significantly reduced growth metrics. Dual infections were not associated with significantly more severe effects on the growth metrics than single infections; the number of triple infections was very low and precluded statistical comparison. Overall, these data suggest that infections by these organisms can be associated with reduced juvenile Chinook salmon growth. Because growth in the first year at sea has been linked to survival for some stocks of Chinook salmon, the infections may therefore play a role in regulating these populations in the Northeast Pacific Ocean.

Effect of Nanophyetus salmincola and Bacterial Co‐Infection on Mortality of Juvenile Chinook Salmon

“…Our results support a previous study that showed encysted N. salmincola metacercariae can increase mortality from a marine bacterial infection in juvenile Chinook Salmon (Jacobson et al 2003). Few studies have investigated co-infection effects of digenean metacercariae and bacterial infections on fish despite the common cooccurrence of these pathogens in juvenile salmonids (e.g., Sandell et al 2015) and other fishes (e.g., Xu et al 2007). Most studies involving larval digenean bacteria co-infection in fish have shown that increased mortality or bacterial invasion occurs when fish are concurrently challenged with cercariae and bacteria (e.g., Bolbophorus spp.…”

“…Macroparasites typically have an aggregated distribution in the wild, with few to no parasites in the majority of hosts and high parasite intensities in a small percentage of hosts (Lester 1984;Ferguson et al 2011a). For example, mean N. salmincola intensities in wild juvenile Chinook Salmon caught off the coast of Oregon and Washington ranged from 18 to 73 metacercariae, but these fish included a small proportion (∼5%) of individuals with intensities exceeding 200 metacercariae (Jacobson et al 2008;Sandell et al 2015). Thus, it is possible the effects of co-infection on mortality occur only in the heavily N. salmincola-infected proportion of the out-migrating population.…”

“…Studies on the pathogenicity of N. salmincola suggest that physical damage from cercarial penetration and migration can cause mortality in salmon fry exposed to a high number (e.g., 200 cercariae) at a time (Baldwin et al 1967); if exposed over a period of time, however, the cercariae will encyst as metacercariae without lethal effects (Millemann and Knapp 1970). Nonetheless, field and laboratory studies indicate that encysted N. salmincola metacercariae can have negative, sublethal effects on swimming ability (Butler and Millemann 1971;Ferguson et al 2012), growth (Sandell et al 2015), osmoregulation enzymes (Ferguson et al 2012), and immune function and disease resistance of juvenile salmonids when challenged with the marine bacteria Vibrio anguillarum (Jacobson et al 2003).…”

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

“…Investigations into the effects of pathogens on the growth of fishes are scarce, with little research having been performed on salmonids (Speare et al ., ) or outside of the laboratory (Sandell et al ., ). For salmonids and other teleosts, body growth can be inferred from their otoliths, the calcified structures in the inner ear whose incremental depositions are proportional to changes in fish length (Campana & Neilson, ; Campana, ).…”

Myxobolus arcticus and Parvicapsula minibicornis infections in sockeye salmon Oncorhynchus nerka following downstream migration in British Columbia

“…In western North America, infections are widespread among Pacific salmon in fresh water and in the ocean (Banner et al 1986, Meyers et al 1993, Kent et al 1998 and also in cultured salmon (Evelyn 1993). The bacterium has frequently been detected in juvenile Pacific salmon in fresh and coastal waters of the western USA (Sanders et al 1992, Arkoosh et al 2004, Van Gaest et al 2011, Sandell et al 2015. The mean prevalence of R. salmoninarum in juvenile Chinook salmon from 12 coastal locations ranged from 10 to 68% (Arkoosh et al 2004).…”