Changes in chloride cell morphometry in response to various salinities in common carp, Cyprinus carpio

Objective: The aim of the present study was to assess effect of salinity on number and size of chloride cells (mitochondria rich cells or MRCs) and their relation to osmoregulatory ability in fresh water (FW) fishes. Method & Materials: Eighty common carps, Cyprinus carpio (800-1000 gr in body weight) were obtained from Shahid Malaki fish farm in Ahwaz and were maintained under lab conditions for adaptation for 30 days and were fed with commercial pellets. They were introduced from fresh water to different salinities of 3, 6, 9 and 12 ppt, respectively with 3 ppt increase daily. When they were reached final salinity, they were adapted to 14 additional days. Some fishes were kept in FW as control. At the end of the period, 5 fish per salinity were killed by destruction of the brain and the second gill arch from right side were dissected and fixed in the buffered formalin following standard methods for 24 h. Paraffin sections of 5 μm thickness were prepared and stained in haematoxilin and eosin. Observations were made with light microscope. Results & Conclusion: After 14 days adaptation to different salinities (0, 3, 6, 9, 12 ppt), diameter and density of MRCs were investigated. Interlamellar MRC diameter and density showed a direct relation with salinity. MRCs in the gill are important in maintaining ionic balance in the fish. Different species have been reported to deploy a range of strategies in hyperosmotic conditions. For example beluga (Huso huso) and Siberian sturgeon (Acipenser baerii) presented a proliferation of branchial MRCs while in Adriatic sturgeon (A. nacarii) a reduction in number of MRCs recorded. In the present study, fishes exposed to isosmotic and hyperosmotic media presented an increase in diameter and density of interlamellar MRCs. It was observed that MRCs of the FW and brakish water adapted common carp were located all over the gill lamellae (lamellar MRCs). Also in this study, there were no significant difference in the density and diameter of MRCs in the lamellar area. Some investigators recorded the similar results in juvenile brook trout, Salvelinus fontinalis and juvenile Gulf of Mexico sturgeon Acipenser oxyrinchus, respectively.

Keywords:

salinities , osmoregulation , Chloride cell , Cyprinus carpio