Effect of Temperature on Survival of Lost River Suckers with a Natural Infection of Ichthyobodo spp.

Abstract

To compensate for low natural survival of endangered Lost River Suckers Deltistes luxatus, the U.S. Fish and Wildlife Service and the Klamath Tribes have initiated captive rearing programs. We conducted laboratory experiments intended to determine the temperature for optimum growth of juvenile Lost River Suckers; however, due to an unanticipated infection with Ichthyobodo spp., we instead estimated survival in conjunction with temperature and parasite loads. Ichthyobodo spp. are common parasites that infest fish skin and gills; they are known to be present in Upper Klamath Lake and have been found in fish at both the federal and tribal fish‐rearing facilities. All fish held at mean temperatures of 16°C and 19°C survived the entire 65‐d experiment, whereas the median time to death was 27 d at 22°C, 8 d at 24°C, and 7 d at 26°C. Gill samples from all Lost River Suckers tested positive for Ichthyobodo spp. DNA, with a trend toward higher copy numbers in suckers that were held at a mean temperature of 22°C or warmer compared to those held at 19°C or cooler. Fish kept at all temperatures grew slowly. These results suggest that survival of Lost River Suckers with a natural infection of Ichthyobodo spp. was significantly impacted by temperature.

Water and Endangered Fish in the Klamath River Basin: Do Upper Klamath Lake Surface Elevation and Water Quality Affect Adult Lost River and Shortnose Sucker Survival?

“…Average water temperatures in 2017 were the highest we recorded from 2005 to 2020. Survival of juvenile suckers infected with Ichthyobodo spp., a common parasite in Upper Klamath Lake, decreases when temperatures exceed 22°C (Martin et al 2021). Increased temperatures also reduce the amount of available oxygen in the water and can increase the metabolic rates and oxygen consumption of suckers (Clarke and Johnston 1999), possibly making them less resilient to hypoxic events and parasites (Mikheev et al 2014).…”

“…For dissolved oxygen, we used the 96-h median lethal oxygen saturation for LRS juveniles of 20.7% (1.62 mg/L at 20°C; Saiki et al 1999) as our lethal threshold and we used the lowest no-effect level for oxygen saturation of 31.3% (2.1 mg/L at 22°C over 14 d; Meyer and Hansen 2002) as our stress threshold. The water temperature at which mortality increased for parasite-infected suckers (24°C) was used as a stress threshold (Martin et al 2021). An un-ionized ammonia concentration of 0.2 mg/L, which causes swelling of gills, was considered a stress threshold (Lease et al 2003).…”

“…The water temperature at which mortality increased for parasite‐infected suckers (24°C) was used as a stress threshold (Martin et al. 2021). An un‐ionized ammonia concentration of 0.2 mg/L, which causes swelling of gills, was considered a stress threshold (Lease et al.…”