Comparing Field Based Temperature Standards to Laboratory Derived Standards for Bluehead Sucker, Flannelmouth Sucker and Roundtail Chub larvae

Authors: Darian Woller, Tawni Riepe, Dana Winkelman

Year: 2024

Abstract

Identifying temperature tolerance ranges is important when assessing risks that impact fish survival. The Colorado Water Quality Control Commission recommends the use of two acute temperature tests when determining temperature criteria to protect aquatic life: incipient lethal temperature tests (ILT) and critical thermal tests (CT) in a controlled laboratory setting. Laboratory-based ILT and CT tests require a static acclimation temperature where fish are hatched, reared, and held at for 14-30 days. However, these laboratory methods do not accurately represent the stream temperature conditions fish encounter in their natural environment, which can affect temperature tolerance. We suggest applying laboratory-based ILT and CT temperature tests in a more biologically appropriate context by using field collected fish and weekly average temperature (WAT) to represent their recent history of temperature exposure instead of the standard acclimation temperature used in laboratory tests. Our study evaluates field derived ILT and CT using the WAT exposure history for three species on the western slope of Colorado: the Flannelmouth Sucker (Catostomus latipinnis), Bluehead Sucker (Pantosteus discobolus), and Roundtail Chub (Gila robusta). Field trials were conducted in the summer of 2024, with larvae collected from Roubideau Creek in a mobile laboratory using stream water. Temperatures were manipulated to assess both ILT and CT. Laboratory trials were conducted at the Colorado Parks and Wildlife toxicology laboratory following standard CT protocols, using larvae that were raised in the laboratory. Flannelmouth Sucker acclimated at 16ºC had a CTMin of 7.2 ± 0.5ºC and a CTMax of 32.6 ± 0.4ºC. Field collected Flannelmouth Sucker with a WAT of 16.7ºC had a CTMin of 8.9 ± 1.4ºC and a CTMax of 32.2 ± 1.8ºC. Bluehead Sucker acclimated at 18ºC had a CTMin of 7.2 ± 1.6ºC and a CTMax of 32.1 ± 2.4ºC. Field collected Bluehead Sucker with a WAT of 16.7ºC had a CTMin of 7.9 ± 0.9ºC and a CTMax of 33.6 ± 0.7ºC. Field collected Roundtail Chub had a CTMin of 7.0 ± 0.2ºC and CTMax of 33.6 ± 0.44ºC with a WAT of 20.9ºC; currently there is no laboratory CT data for Roundtail Chub larvae. Larvae were tested at UILT treatments of 28.0ºC, 27.7ºC, 26.1ºC, 25.7ºC, and 19.4ºC for seven days. Preliminary UILT results suggest that mortality was highest at the warmest temperatures (28.0ºC, 27.7ºC, and 26.1 ºC) with the lowest mortality occurring near the WAT of 20.9ºC. Ultimately, our findings should address whether field or laboratory methods should be used when developing temperature standards.