The Effect of Starvation and Refeeding Periods on Iono-osmoregulation of 2+ Caspian Trout

Effects of different nutritional conditions on iono-osmoregulation in juvenile of Caspian trout (Salmo trutta caspius) parrs were studied. Following adaption to the new environment, 750 Caspian trout parrs (12.5±1 g) were kept under the treatments of six weeks of full feedings (FFF), three weeks of feeding-three weeks of starvation (FS), six weeks of starvation (SSS), two weeks of feeding-two weeks of starvation-two weeks of re-feeding (FSF) and three weeks of starvation-three weeks of re-feeding (SF). Fish were fed with rainbow trout commercial feed three times a day up to satiation. There was no significant difference in serum sodium, chloride, potassium and magnesium between treatments, but serum osmolality decreased from 299 mOsmolkg-1 in FFF to 286 and 271 mOsmolkg-1 in FS and SSS (P <0.05), and re-feeding, after starvation periods, compensated the osmolality reduction to the similar levels in FFF. Five days after transferring the parrs to Caspian Sea (salinity: 13 gL-1), serum magnesium reached to 3.55 and 3.40 mEqL-1 in FS and SSS respectively (P <0.05), in comparison to FFF group (2.36 mEqL-1). Serum potassium showed also irregular significant difference between treatments (P <0.05), while chloride and sodium presented no significant difference. Serum osmolality levels increased to a maximum of 415 mOsmolkg-1 in FS and were decreased to a minimum of 306 mOsmolkg-1 in SSS (P<0.05), compare to FFF (366 mOsmolkg-1). We concluded that starvation has negative effects on ion regulatory capacity of Caspian trout parrs and although re-feeding can increase this capacity but effects of long period starvation cannot be compensated.