Physiological and Behavioural Responses of Largemouth Bass Yearlings (Micropterus salmoides) to Hypoxia at Summer and Winter Temperatures

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Li, Vera
Fish , Biology
The main objective of this thesis was to determine the metabolic and behavioural outcomes from hypoxia exposure to largemouth bass (Micropterus salmoides) yearlings when acclimated to either winter (5°C) or summer (20°C) temperatures. This was achieved by exposing largemouth bass to varying levels of hypoxia and subsequently quantifying metabolites, in addition to observing behavioural patterns. The critical partial pressure of oxygen was also determined for fish at both temperatures. Hypoxia experiments revealed that metabolite concentrations increased or decreased significantly compared to control values as hypoxia levels intensified at 20°C, however there were minimal changes for fish at 5°C. More specifically, end product concentrations of lactate increased, while substrate concentrations of ATP, PCr and glycogen decreased and glucose concentrations did not change significantly at 20°C. It was also found that the magnitude of change was greater for fish at 20°C, indicating the impact of hypoxia is greater at warmer temperatures. In addition, it was noted that hypoxia experiments performed at either identical percent oxygen saturation (%) or identical dissolved oxygen (mg/L) resulted in very similar metabolite trends at both temperatures. In terms of behaviour, ventilation rates increased significantly and peaked at 2mg/L for largemouth bass at 20°C, however there was no change for fish at 5°C. There were also more instances of aquatic surface respiration with increasing hypoxia for fish at 20°C, but nearly no attempts at 5°C. Critical partial pressure of oxygen (Pcrit) values were calculated to be 1.36 ± 0.02 mg/L (16% oxygen saturation) for 20°C and 0.77 ± 0.04 mg/L (5% oxygen saturation) for 5°C fish respectively. The Pcrit levels corresponded to the hypoxia levels that initiated changes in metabolite concentrations at each temperature, thus indicating that largemouth bass undergo anaerobic metabolism. This study shows that the overall impact of hypoxia on largemouth bass yearlings was much greater in warmer water. These results indicate that hypoxia may become a very important physiological stress on younger life stages of fish as water temperatures increase with climate change.
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