The Effect Of Temperature On Critical Oxygen Tension (P_crit) And Gill Morphology In 6 Carps

To investigate the temperature effect on RMR, P_crit and gill morphology in junvenile Spinibarbus sinensis, Parabramis pekinensis, Ctenopharyngodon idellus, Aristichthys nobilis, Hypophthalmichthys molitrix and Cyprinus carpiovar Jian. We firstly randomly allocated fishes at 5 rearing temperatures (10℃,15℃,20℃,25℃,30℃) for 2 weeks. Then determined RMR by using sealed respirometry, calculated P_crit by"two-line"regression method. The second gill arch from the right hand side of 3 fish from species at each rearing temperature was carefully dissected out, rinsed and fixed for later scanning electron microscopy. We hope that our study could explore the hypoxia tolerance mechanism in warm water carp from different vertical habitants and provide practical information for protection of fish resources in the Three Gorges reservoir region.The results are:1. Effect of temperature and genus on RMRTemperature and genus together have significant effect on RMR in juvenile carps ( interaction effect P<0.05). The RMR of all experimental species elevated along with rearing temperature (10℃,15℃,20℃,25℃,30℃). The magnitude and rising pace was in accordance with species characteristics. At most rearing temperature, there were significant differences in RMR among species (P<0.05); only at 25℃, all except Aristichthys nobilis reached to a similar zone in RMR level. Put the genus factor aside, temperature has profound effect on RMR within species (P<0.05), the effect was represented in different patterns.2. Effect of temperature and genus on P_critTemperature and genus together have significant effect on P_crit in juvenile carps (interaction effect P<0.05). At each rearing temperature, genus has significant effect on P_crit (P<0.05), two levels were revealed: at most temperature groups (10℃, 15℃, 20℃,25℃), the P_crit of Aristichthys nobilis, Hypophthalmichthys molitrix and Cyprinus carpiovar Jian were significant lower than that of Spinibarbus sinensis, Ctenopharyngodon idellus and Parabramis pekinensis. P_crit value of all species reach a similar level at 30℃, except Spinibarbus sinensis. Within species, the temperature effect on P_crit represented 3 types: Temperature had significant effect on P_crit in Spinibarbus sinensis, Parabramis pekinensis and Ctenopharyngodon idellus (P<0.05). With ascending temperature, Spinibarbus sinensis had its P_crit increased from 17.05±1.25 (torr) to 24.82±1.80 (torr); the P_crit values of Parabramis pekinensis and Ctenopharyngodon idellus decreased from 29.20±4.33, 21.70±2.51 to 16.70±0.91, 15.37±1.09, separately. Hypophthalmichthys molitrix and Cyprinus carpiovar Jian'P_crit values showed a firstly increased, then dropped pattern, with a peak P_crit values at 20℃. Though temperature had significant effect on P_crit in Aristichthys nobilis (P<0.05), its P_crit changing type was similar to Hypophthalmichthys molitrix and Cyprinus carpiovar Jian's, of which was not affected by temperature change.3. Effect of temperature on gill morphology in carps.We first found that the gill plasticity existed in Ctenopharyngodon idellus, Aristichthys nobilis, and Hypophthalmichthys molitrix due to temperature changes. At lower temperature, the lamellae were embedded with a large interlamellar cell mass (ILCM), resulting in a sausage-like morphology. As temperature went higher, through a apoptosis and cell cycle arrest process, the gills transformed into'normal'gills with protruding lamellae. However, Spinibarbus sinensis, Parabramis pekinensis and Cyprinus carpiovar Jian didn't have such gill remodeling potential.In conclusion:1. The RMR in carps elevated along with rearing temperature grew; the magnitude and rising pace was in accordance with species characteristics. Most carp's RMR reached a similar zone at 25℃, which suggested 25℃might be the optimal temperature for warm water carps.2. The P_crit responses towards temperature varied among species, which revealed 3 patterns: increasing, decreasing and being conservative along with temperature elevation. The wild distribution has no relation with P_crit.3. The gill plasticity has no relation with P_crit. The oxygen acquisition and ion endogenous balance trade off might be the driven force of gill remodeling.