Swimming Endurance in Juvenile Chinook Salmon Infected with Salmincola californiensis

Abstract

Juvenile Chinook Salmon Oncorhynchus tshawytscha moving downstream through tributaries of the upper Willamette River basin can spend months in reservoirs created by dams. While residing in the reservoirs, they often obtain heavy infections of the freshwater parasitic copepod Salmincola californiensis. The physiologic effect these parasites have on salmonids is poorly understood. We developed a method to infect juvenile Chinook Salmon in a laboratory with the copepodid stage of S. californiensis. Infected and uninfected fish were subjected to a swimming challenge to ascertain swimming endurance. Severity of gill damage was assessed using a dissecting microscope. Juvenile Chinook Salmon naturally infected with S. californiensis in Cougar Reservoir, Oregon, were also challenged and compared with their lab-infected counterparts. Copepod infection greatly impaired the swimming ability of laboratory fish, and the naturally infected fish were entirely incapable of swimming at low velocity. Chinook Salmon collected in the wild were more heavily infected than the laboratory fish and had trouble surviving collection and transport to our laboratory. The intensity of infection and severity of gill damage were positively correlated with diminished swimming ability, suggesting that heavy infection with copepods impairs gas exchange and osmotic regulation, which likely results in diminished fitness and decreased survival of infected fish.

Laboratory infection rates and associated mortality of juvenile Chinook Salmon (Oncorhynchus tshawytscha) from parasitic copepod (Salmincola californiensis)

“…Here, we report for the first time that these severe changes occur before parasites moult into adults, in agreement with Herron et al., (2018) where severe truncation of the gills was observed without the presence of adult copepods. The copepodid and chalimus stages also caused mortality as their intensity was associated with increased mortality before adult females were observed.…”

“…Sutherland and Wittrock (1985) suggested that truncation of the filaments was due to failure of growth at the infected filaments. However, this profound change occurred within weeks in our study and in the laboratory study by Herron et al., (2018), which is too short of time for normal gill primary filaments to grow to any extent. A more likely cause is direct damage to filaments, including the cartilage support by feeding by the copepods.…”

Hatching and survival of the salmon ‘gill maggot’ Salmincola californiensis (Copepoda: Lernaeopodidae) reveals thermal dependence and undocumented naupliar stage

“…Commonly referred to as ‘gill-maggots’ Salmincola spp. can cause mechanical gill damage, anaemia, increased difficulty with osmoregulation, as well as impair swimming ability (Pawaputanon, 1980; Sutherland and Wittrock, 1985; Herron et al ., 2018). There are indications that S. californiensis may also harbour the pathogenic, and potentially lethal, bacteria Aeromonus salmonicida, which also infects salmonids (Herron-Seeley, 2016).…”

Hiding in Plain Sight: Historical Fish Collections Aid Contemporary Parasite Research

“…californiensis can impair fish condition with substantial gill damage and reductions in swimming ability (Pawaputanon ; Herron et al. ). These infections appear to be common for salmonids in North America's Pacific Northwest reservoirs, with especially high infection prevalence and intensity noted for juvenile spring Chinook Salmon Oncorhynchus tshawytscha (Monzyk et al.…”