Evaluation of methodology for measuring standard metabolic rates of crayfishes using the red swamp crayfish Procambarus clarkii (Girard, 1852) (Decapoda: Astacidea: Cambaridae)

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Abstract
The importance of energy budgets in understanding the ecology, conservation and production of crayfishes has long been recognized. Standard metabolic rate (SMR) estimates the minimum metabolic rate required for basic maintenance of an organism while at rest, and is a critical parameter for investigating energy balance and metabolism. Estimating SMR involves quantifying oxygen uptake under specific conditions. Standard methodology for estimating SMR has been described and evaluated for fishes, but not thoroughly investigated for crayfishes. We adapted a recommended protocol developed for fishes in order to determine appropriate methodologies for measuring SMR in crayfishes. Study animals consisted of 18 individuals of Procambarus clarkii (Girard, 1852) collected in Alabama, USA. Respiration rates were measured using an optical respirometry system (Loligo Systems®; Viborg, Denmark) and intermittent respirometry techniques. Crayfish respiration stabilized the morning after initiation of the trial indicating that a 12 h overnight period was sufficient to acclimate crayfish to respirometry chambers. After 12 h of daylight, respiration of acclimated crayfish typically exhibited a short spike when lights were turned off, indicating data collected within ~2 h following a light change should be excluded from the dataset used to calculate SMR. When calculating SMR, a quantile approach was typically more appropriate than the mean of the lowest normal distribution approach. SMR calculated during the day was only marginally higher than SMR calculated during the night, indicating that SMR can be estimated during either period if shelters are provided in the respiration chambers. Due to the wide diversity of crayfish species and ranges, our recommendations may not be appropriate for every crayfish species or subpopulation. The recommendations can serve, however, as a valuable starting point and the described methodology provides a standardized approach for determining appropriate protocols to measure SMR of crayfish species of interest.

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