Abstract
The effects of different water salinities on the number and area of chloride (mitochondriarich) cells and on plasma glucose level in Sparidentex hasta were studied. Fish were exposed to a salinity of 5, 20, 40, and 60 ppt for 14 days. The group kept at 40 ppt was considered as the control. Samples were collected at 6 and 12 h and on days 1, 2, 7, and 14 of exposure. The results of this study revealed changes in the plasma glucose level and in the number and area of chloride cells in S. hasta associated with water salinity variations. It can be concluded that S. hasta has a wide tolerance towards salinity changes in the environment, which is provided by the mechanisms of osmoregulation and the involved organs, mostly by gills.
Highlights
Life in two environments with different chemical compositions and osmotic pressures and movements between them require a specific compromise and physiological and tissue adaptations for maintaining homeostasis and normal life functions
By the end of the adaptation period, the fish were assigned to 12 tanks (15 fish per tank) with the volume of 300 L filled with water with different salinity levels of 5, 20, 40, and 60 ppt for 14 days (3 tanks per each salinity level)
At 24 h, the glucose level decreased significantly in the treatment of 5 ppt compared to the control group (P < 0.05)
Summary
Life in two environments with different chemical compositions and osmotic pressures and movements between them require a specific compromise and physiological and tissue adaptations for maintaining homeostasis and normal life functions. Some hormonal and enzyme mechanisms, as well as tissue modifications, especially in gills, can be used to regulate osmotic stress for overcoming various stress conditions [Baldisserotto et al, 2007]. Gill epithelium consists of different cells, the most important of which are mucosal, squamous, and chloride (mitochondria-rich) cells. Depending on the salinity of the environment, the gill epithelium pumps salt against the osmotic concentration outside or inside the body, which is an activity performed by most of chloride cells [Khuder et al, 2016]. Gills play an important role in keeping ion and acid-base equilibrium in both fresh-water and saline-water environments [Evans et al, 2005]. When moving from fresh water to saline water, euryhaline fish have to change their gills from an ion absorption structure to a secretory structure [Marshall et al, 2002]. The increase in the size and number of chloride cells is one of effective mechanisms of resistance to salinity variations [Uchida et al, 1996]
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