WINSTEAD, C. J.*; CLAUSSEN, D. L.: Cardiorespiratory responses of the Asian prawn, Macrobrachium rosenbergii to temperature and hypoxia

Macrobrachium rosenbergii may experience thermal and hypoxic stresses during their commercial cultivation and during transport of stock or post-harvest animals. We used noninvasive methods to monitor cardiac responses, scaphognathite beating, and activity of juvenile and adult animals subjected to cyclic temperature changes between 20 and 30 C. Half of the prawns were further exposed to moderate hypoxia (2 – 4.5 ppm O₂) during the experimental protocol. Changes in heart width during the cardiac cycle were used to estimate stroke volume and cardiac output. Diastolic heart width exhibited a slight positive allometry with a scaling exponent of about 0.41. Overall, the effects of hypoxia were small and those of activity were inconsistent; however, both temperature and body size had a substantial influence on cardiorespiratory responses. The mean Q₁₀s for heart rate (1.73) were greater than those for scaphognathite frequency (1.53). The Q₁₀ response of heart rate was greater between 25 and 30 C than between 20 and 25 C, and this difference was greater for smaller than for larger prawns. The scaling exponents for heart rate averaged about -0.10. Unlike heart rates, estimated stroke volumes and cardiac outputs did not respond to temperature in a consistent manner, but had mean scaling exponents of 1.09 and 0.99 respectively. Scaphognathite frequency responded to temperature, with scaling exponents of about -0.16. Giant Asian prawns are not overly sensitive to moderate hypoxia, and brief bouts of activity have only a modest impact on their subsequent cardiorespiratory responses. The prawns do not appear to be greatly stressed by temperature changes within the 20 to 30 C range, but their cardiorespiratory responses, especially those of juveniles, are clearly influenced by temperature. �