Effect of temperature on critical oxygen tension (Pcrit) and gill morphology in six cyprinids in the Yangtze River, China

We evaluated the hypoxia tolerance capacities of fish in response to a range of temperatures which they often experience in aquaculture. We selected six cyprinids in the Yangtze River that were closely related in their phylogeny and widely used in the Chinese aquaculture industry as experimental animals: juvenile qing bo Spinibarbus sinensis, Chinese bream Parabramis pekinensis, grass carp Ctenopharyngodon idellus, big head carp Aristichthys nobilis, silver carp Hypophthalmichthys molitrbc and common carp Cyprinus carpiovar Jian. We measured individual metabolic rate (MO2) and calculated the routine metabolic rate (RMR), Q(10) and critical oxygen tension (P-crit) after two weeks of acclimation at either 10, 15, 20, 25 or 30 degrees C. Gill morphology was also examined. A variety of P-crit responses was observed: the P-crit increased (qing bo), decreased (Chinese bream and grass carp) or was conserved (big head carp, silver carp and common carp) with increasing acclimation temperatures (10 - 30 degrees C). Apparent thermal-induced gill remodeling was found in three (grass carp, big head carp and silver carp) of the six cyprinids studied, with common carp also exhibiting some degree of gill structure modification. RMR was positively correlated with P-crit at temperatures ranging from 10 to 30 degrees C in qing bo and big head carp; however, such significant correlation was not found in the remaining cyprinids, possibly due to their gill remodeling potential during thermal changes and thus an increased lamellar surface area at higher temperatures.