The effects of temperature and dissolved oxygen on fish respiration determined by enzymatic and organismal techniques
Type of DegreePhD Dissertation
School of Fisheries, Aquaculture, and Aquatic Sciences
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One of the greatest threats to freshwater biodiversity is anthropogenic alteration to habitat. Temperature change is one of the most important anthropogenic impacts, especially for ectotherms that experience the effects of temperature fluctuations more intensely than their endothermic counterparts. Fish biodiversity in Alabama is nearly unrivaled, and to maintain diversity in these systems impacted by anthropogenic stressors, management decisions must be well-informed. Successful management and/or policies are based on information from all relevant aspects of ecosystems, and to that end, in this study I use both game and non-game fish to quantify performance, hypoxia tolerance, and oxygen regulation across a temperature range. I use multiple metrics (metabolic rate, critical oxygen level [DOcrit], and regulation index [RI]) to examine temperature effects at the organismal level and use respiratory enzyme assays to quantify thermal performance at the enzymatic level. In addition, I examine the same organismal level metrics in my examination of a potentially compounding stressor: glochidia infestation. Additional stressors may exacerbate temperature fluctuation effects, and a naturally-occurring stressor for some fish species is as a host for parasitic mussels. In an effort to quantify this possible glochidia-induced stress, juvenile bluegill Lepomis macrochirus and largemouth bass Micropterus salmoides were infested with glochidia and monitored for 11 weeks. At the whole-organism level, metabolic rates were affected by temperature in all non-game species, but temperature effects on DOcrit and RI varied. When significant, DOcrit increased with temperature while RI was inversely related to temperature. No significant effect of glochidia infestation was found for either gamefish species. At an enzymatic level, enzyme optima and performance were quantified for game and non-gamefish. Performance of enzymes and optimum temperatures varied among species. These results emphasize that fully-informed and comprehensive management decisions must consider the variable responses to temperature fluctuations across fish genera (including potential mussel hosts). Further, multiple physiological metrics provide a more complete picture, and therefore need to be considered when assessing fish thermal performance.