Physiological, biochemical and morphological indicators of osmoregulatory stress in `California' Mozambique tilapia (Oreochromis mossambicus×O. urolepis hornorum) exposed to hypersaline water

Abstract

SUMMARYThe salinity tolerance of the `California' Mozambique tilapia(Oreochromis mossambicus × O. urolepis hornorum), a current inhabitant of the hypersaline Salton Sea in California, USA, was investigated to identify osmoregulatory stress indicators for possible use in developing a model of salinity tolerance. Seawater-acclimated (35 g l–1) tilapia hybrids were exposed to salinities from 35–95 g l–1, using gradual and direct transfer protocols, and physiological (plasma osmolality, [Na+],[Cl–], oxygen consumption, drinking rate, hematocrit, mean cell hemoglobin concentration, and muscle water content), biochemical(Na+, K+-ATPase) and morphological (number of mature,accessory, immature and apoptotic chloride cells) indicators of osmoregulatory stress were measured. Tilapia tolerated salinities ranging from 35 g l–1 to 65 g l–1 with little or no change in osmoregulatory status; however, in fish exposed to 75–95 g l–1 salinity, plasma osmolality, [Na+],[Cl–], Na+, K+-ATPase, and the number of apoptotic chloride cells, all showed increases. The increase in apoptotic chloride cells at salinities greater than 55 g l–1, prior to changes in physiological and biochemical parameters, indicates that it may be the most sensitive indicator of osmoregulatory stress. Oxygen consumption decreased with salinity, indicating a reduction in activity level at high salinity. Finally, `California' Mozambique tilapia have a salinity tolerance similar to that of pure Mozambique tilapia; however, cellular necrosis at 95 g l–1 indicates they may be unable to withstand extreme salinities for extended periods of time.

Prolonged apoptosis in mitochondria-rich cells of tilapia (Oreochromis mossambicus) exposed to elevated salinity

“…The prolonged time-course of apoptosis in MRC is supported by an earlier electron microscopy study that showed that tilapia MRC apoptosis is signiWcantly increased several days after transfer from FW to SW (Wendelaar Bonga and Van Der Meij 1989). In addition, our results agree with a previous study that predicted that tilapia increase apoptosis by two-to threefold several days after acute salinity stress for every 20-30 g/l increase in salinity (Sardella et al 2004b).…”

Tilapia (Oreochromis mossambicus) brain cells respond to hyperosmotic challenge by inducingmyo-inositol biosynthesis

“…In contrast, tilapia transferred to 60 ppt salinity were able to return to lower plasma osmolality values following 24 h exposure (Sardella et al, 2004). The present study and others clearly demonstrate that fish are able to tolerate much larger deviations from the plasma osmolality set point than their mammal counterparts (Evans and Claiborne, 2006).…”

“…This increase has not been previously documented in other work performed in tilapia (Kammerer et al, 2010;Sardella et al, 2004). However, Kammerer et al (Kammerer et al, 2010) observed significantly increased opercular ventilation at 3 h and a significant increase in respiration at 24 h in tilapia that were acutely exposed to 25 ppt salinity challenge.…”

“…Surprisingly, we found that plasma osmolality in chronic acclimation was maintained at elevated levels (~475 mOsm kg -1 ) for 24 h without mortality. Sardella et al (Sardella et al, 2004) reported that Mozambique 'hybrid' tilapia kept at 95 ppt salinity for 5 days following transfer maintained an elevated plasma osmolality of ≥450 mOsm kg…”

Effect of different levels of salinity on gill and kidney function in common carpCyprinus carpio(Pisces: Cyprinidae)

“…The increase in plasma Na + content as found in the current study is a common response of stenohaline species to salinity challenges (De Boeck et al 2000;Eckert et al 2001;Tam et al 2003;Benli & Yildis 2004). These increases could be the consequence of increase in Na + -K + ATPase, which is a good indicator of an osmoregulatory challenge, such as seen in euryhaline fish (Sardella et al 2007). The significant increase in plasma Na + and Cl − observed at salinities of 9 and 12 g/l suggests that the tolerance limit to salinity in common carp is around these values, as in salinity of 15 g/l all fish died (unpublished data).…”