Yellowtail kingfish
Scientific name: Seriola lalandi
Tolerance to acute CO2 exposure
The live transport of fish in enclosed systems exposes the fish to elevated dissolved carbon dioxide (CO2) levels (termed hypercapnia) due to the CO2 excreted by respiration. The high solubility of CO2 means that the blood and water CO2 concentrations are closely correlated. When the partial pressure of CO2 in blood rises, body tissues become acidified through the formation of carbonic acid, which in turn causes a variety of physiological problems, including red blood cell swelling and reduced muscle and nerve performance.
We undertook a study to measure the effect of acute hypercapnia on yellowtail kingfish juveniles, so that we could gain a better understanding of this species' ability to cope with live transport from the hatchery to fish farms. In the first trial, a live transport event was simulated where the CO2 concentration was varied. During commercial transports, the CO2 concentration varies depending on fish acitivity, water temperature and degassing/aeration efficiency.
As has been observed from commercial transports, the juveniles coped well with the simulated transport , despite being exposed to relatively high concentrations of CO2. Commonly measured physiological stress indicators such as blood glucose and lactate levels, and muscle pH and lactate levels did not greatly vary between transported and control individuals during the simulated transport or subsequent recovery.
A second trial was undertaken to measure the effect of CO2 concentration on blood physiology parameters. The blood is useful for studying the effects of hypercapnia as it transports gases within the body and regulates the acidifying effects of CO2 by changing buffering capacity. Fish were exposed to three levels of CO2 for 5 hours. The CO2 levels represented a low, moderate and high degree of hypercapnia. The degree of red blood cell swelling and blood haemoglobin concentration were measured. The more swollen a red blood cell and the lower the haemoglobin concentration, the more difficult it is for the fish to transport oxygen.
The above figure shows that after 5 hours exposure,the moderate and high CO2 concentrations caused a lowered haematocrit, indicative of red blood cell swelling. Mean cell haemoglobin concentration (MCHC) decreased mid-way through the simulated transport in the moderate and high CO2 concentrations, indicative of a reduced blood oxygen carrying capacity. The effects of CO2 exposure were not evident 1.5 days after the simulated transport.
In summary:
- Yellowtail kingfish juveniles cope well with acute exposure to fluctuating and elevated CO2 concentrations.
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This research was funded by the NZ Foundation for Research Science and Technology, and was carried out during my employment at the NIWA Bream Bay Aquaculture Park. I was supported by a NZ Tertiary Education Commission Bright Futures Doctoral Scholarship.
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This research has been published and is available as follows:
Moran, D., Wells, R.M.G., Pether, S.J., (2008). Low stress response exhibited by juvenile yellowtail kingfish (Seriola lalandi Valenciennes) exposed to hypercapnic conditions associated with transportation. Aquaculture Research, 39:1399-1407.
doi: 10.1111/j.1365-2109.2008.02009.x ------- get PDF of paper