GILL LICE SALMINCOLA CALIFORINESIS: IMPLICATIONS TO COLORADO FISHERIES MANAGEMENT

Abstract

ABSTRACT GILL LICE SALMINCOLA CALIFORNIENSIS: IMPLICATIONS TO COLORADO FISHERIES MANAGEMENT Gill lice, Salmincola spp., are external parasitic copepods that target many different species of fish across the northern hemisphere. Gill lice limit oxygen exchange through gill filaments on which they are attached and negatively impact fish behavior, immune system function, growth, temperature tolerance, sexual maturation, fecundity, and survival. In Colorado, gill lice were first documented in the early 1900s but were not considered a threat to fish populations until recently. In the early 2000s, gill lice were documented in a Colorado reservoir that subsequently experienced a significant decline in kokanee salmon (Oncorhynchus nerka) populations. This population decline was attributed to gill lice infection coupled with unfavorable environmental conditions.Colorado Parks and Wildlife became concerned by the apparent effects of gill lice on this population and determined that research was warranted to identify and characterize the potential threat that gill lice pose to the state's fisheries. The first priority of my research was to identify which species of gill lice were present in the state and, therefore, identify which host species of fish in the state may be at risk of gill lice infection. In addition to species identification, mapping the current extent of gill lice infection in the state was prioritized. The statewide sampling iii efforts identified one species of gill lice, Salmincola californiensis, which infects Pacific Salmonids of the Oncorhynchus genus. Rocky Mountain Cutthroat Trout (Oncorhynchus virginalis) have been documented as susceptible to S. californiensis; however, no infections were found during statewide sampling efforts. The absence of gill lice infections in Rocky Mountain Cutthroat Trout in the state prompted a susceptibility experiment. I conducted research to investigate gill lice infection and mortality rates between a known gill lice host, Rainbow Trout Oncorhynchus mykiss, and the Rio Grande Cutthroat Trout (Oncorhynchus virginalis virginalis) subspecies of Rocky Mountain Cutthroat Trout. In this experiment, I also examined four distinct habitat types to determine whether habitat influenced infection or mortality in either species. I used a generalized linear mixed-effect model (glmer) in R (version 1.3.1073) to analyze these relationships. Estimated marginal means were used to generate pairwise comparisons for the probability of infection and survival between the two species. I determined that Rio Grande Cutthroat Trout are susceptible to S. californiensis infection and were infected at similar rates to those of Rainbow Trout. I also found that habitat may influence infection rates for both species. Unfortunately, no inferences of infection-causing mortality were possible due to the difficulty in identifying gill lice on decomposed or missing carcasses. The results of this study provide a baseline for gill lice research in the State of Colorado and help to inform fisheries managers of the potential risks associated with S. californiensis infections.