The Israeli Journal of Aquaculture Bamidgeh 56(1), 2004, 51-58.

SHORT COMMUNICATION

CHANGES IN BLOOD ION LEVELS AND MORTALITY RATES IN DIFFERENT SIZED RAINBOW TROUT (ONCORHYNCHUS MYKISS) FOLLOWING DIRECT TRANSFER TO SEA WATER


Ali Turker1, Sebahattin Ergun2 and Murat Yigit2*

1 Department of Aquaculture, Faculty of Fisheries, Ondokuz Mayis University, Sinop 57000, Turkey

2 Department of Aquaculture, Faculty of Fisheries, Canakkale Onsekiz Mart University, Canakkale 17100, Turkey


(Received 11.6.03, Accepted 9.8.03)


Key words: blood ion, mortality, rainbow trout, adaptation to sea water


Abstract


Plasma ion values and mortality rates were compared for 450 rainbow trout (Oncorhynchus mykiss) of three sizes following direct transfer from fresh water to Black Sea water of about 18 ppt. In fish of 14.290.30 g, plasma Na+, Cl- and K+ levels significantly (p<0.05) rose above initial values five days after the transfer and peaked at 178.65.66, 153.90.14 and 1.140.04 mM/l, respectively. In 20.450.48 g fish, these values also rose significantly, reaching 172.44.24, 151.86.65 and 0.980.04 mM/l by day 5. In fish of 29.910.99 g, however, plasma Na+ and Cl- concentrations peaked 19 days after transfer, reaching only 165.56.43 and 142.98.34 mM/l, while plasma K+ reached its highest concentration of 1.020.06 mM/l on day 12, All three concentrations dropped to near initial values on day 26. In all groups, the plasma Ca2+ level rose significantly (p<0.05) above the initial value five days after transfer and then declined while the plasma P5+ concentration dropped on day 5, reaching a minimum on day 12 and recovering the initial level on day 26. The lowest mortality (8.01.89%) was recorded in the 30 g group, followed by 19.30.94% and 24.70.94% in the 20 g and 14 g groups. The failure of the smallest fish to adapt after direct transfer to sea water was likely due to excessively high plasma Na+ and Cl- concentrations and tissue dehydration, indicating that fish of 30 g best adapt to a seawater environment of 18 ppt.

* Corresponding author. Fax: +90-286-2180543, e-mail: muratyigit@comu.edu.tr
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