The Effects Of Diel-Cycling Hypoxia Acclimation On The Hypoxia Tolerance,Swimming Capacity And Growth Performance Of Southern Catfish (Silurusmeridionalis Chen)

To investigate the effects of diel-cycling hypoxia acclimation on the hypoxia tolerance, swimming and growth performance of juvenile southern catfish, we initially measured the critical oxygen tension (Pcrit), oxygen thresholds of aquatic surface respiration (ASR) and loss of equilibrium (LOE) of diel-cycling hypoxia-acclimated (15d,7:00-21:00, dissolved oxygen level (DO)=7.0±0.2mg L-1;21:00-7:00, DO=3.0±0.2mg L-1) and non-acclimated (15d, DO=7.0±0.2mg L-1) southern catfish at25℃We then measured the critical swimming speed (Ucrit) and metabolic rate (MR) of hypoxia-acclimated and non-acclimated fish (under both hypoxic and normoxic conditions). The feeding rate (FR, feeding efficiency (FE) and specific growth rate (SGR) of fish in hypoxia-acclimated and non-acclimated groups were also measured.The results as follows:1. The Pcrit, ASR and LOE of hypoxia-acclimated fish were1.24±0.18(23.02±1.98torr),0.28±0.03and0.03±0.01mg L-1, respectively, which were significantly lower than those of non-acclimated fish (1.62±0.10(28.94±2.12torr),0.35±0.01and0.09±0.01mg L-1, respectively.2. Hypoxia acclimation resulted in a significantly higher Ucrit when the individuals swam in hypoxia. The Ucrit, maximum metabolic rate (MMR) and metabolic scope (MS) of both the hypoxia-acclimated and non-acclimated fish all decreased with the decrease of DO. However, the Ucrit, MMR and MS decreased by31,43and54%, respectively, in non-acclimated fish, whereas these values decreased by15,28and29%, respectively, in hypoxia-acclimated fish, which suggests that hypoxia-acclimated fish were less sensitive to the DO decrease.3. The FR, FE and SGR all decreased by21,20and45%, respectively, in the hypoxia-acclimated group compared to the non-acclimated group. The indications as follows:1. Diel-cycling hypoxia acclimation improved the hypoxia tolerance and aerobic swimming performance of southern catfish, whereas impaired the growth performance.2. The high hypoxia tolerance and physiological plasticity to hypoxia-acclimated southern catfish may be related to its lower maintenance energy expenditure, sit-and-wait lifestyle and bottom-dwelling living environment condition (usually facing oxygen fluctuation). The growth performance of so-called’visceral type’fish species, such as southern catfish, are more sensitive to hypoxia compared to other fish species because of their high peak post-prandial metabolic rate, which may be restrained by the limited aerobic metabolic scope in hypoxia.