Physiological responses to salinity stress in the Managua Cichlid,<i>Cichlasoma managuense</i>
Chunxiang Ai, Xifei Chen, Ziqing Zhong, Yunxia Jiang
Abstract
The present study was designed to examine the physiological responses of juvenile managua cichlid, Cichlasoma managuense under short-term salinity stress, that is transferring C. managuense from freshwater to brackish water of salinity 0 (control group), 3‰, 6‰, 9‰, 12‰ or 15‰ for 48, 96, 144 and 192 hr respectively. The results showed that gill Na+/K+-ATPase (NKA) activity revealed a decreased (48 hr), increased (96 hr) and then slightly decreased (144 hr, 192 hr) response with increasing salinity and the lowest NKA level was consistently detected at 9‰ salinity treatment; gill Ca2+/Mg2+-ATPase (CMA) activities in all salinity treatments were significantly higher than that of the control group (p < .05) before 144 hr; the RNA/DNA ratio was significantly reduced when exposed to high salinities (≥9‰), suggesting growth inhibition; serum cortisol level gradually decreased at low salinities (up to 6‰) but dramatically increased at high salinities of 12‰ and 15‰; and both serum glucose/lactic acid levels and heat shock protein 90 (HSP90) level in liver/muscle were decreased at the salinity between 9‰ and 6‰ but increased at the salinity between 12‰ and 15‰, which was a U-shape response curve. Taken together, our data suggest that C. managuense can adapt well at salinity up to 0‰–9‰ and high salinity may cause detrimental effects.