EFFECTS OF FISH TRANSPORT ON CORTISOL AND GLUCOSE LEVELS OF RAINBOW TROUT (Oncorhynchus mykiss, W.)  

Stress has two different effects on fish and these are grouped into direct and indirect effects. Cortisol and glucose changes and haematological values are included into the direct stress effects (Tapia et al., 2012). Fish transport is an important process in fish farming and it causes acute stres on fish (Abreu et al., 2008). The aim of this study is to inform comparison of cortisol and glucose levels of fish which were transport from commercial fish farm to research laboratory conditions and control group. Rainbow trout were transported from the commercial farm to the research laboratory. After transportation, the fish were examined as clinical findings and stres response parameters blood glucose and plasma cortisol were examined for each fish sample. The fish were firstly anesthetized with cloves oil (75 mg/L for 15 min.) and then the body weights of the fish were measured. For control group, the study was carried out at the field conditions and these fish were not transported. For plasma cortisol analysis, 1 ml of blood was collected from the caudal vein of the fish samples. The blood lettig from the fish was taking within 30 sec. because of cortisol level rising related stress. 20 µl of blood sample was used for glucose level determination. The glucose levels were measured by using glucose meter during the sampling. For cortisol analysis, the blood was taken into the eppendorf tubes containing EDTA and then the samples were allowed to clot for 2-3 h on the ice. After clotting, the upper part of the clotting blood was removed by using a micropipette and stored until analysis. The cortisol levels were determined by using ELIZA method which was done by a private laboratory. The results of both cortisol and glucose levels were evaluated according to Iwama (2004). The mean fish weights were 160 g. Plasma cortisol analyses showed that the levels changed from 5.0 µg/dL to 9.9 µg/dL and blood glucose levels were 3.16 mmol/L . Plasma cortisol levels of the control group was 0.5 µg/dl and blood glucose levels of the group were 3.12 mmol/L. Iwama (2004) reported that plasma cortisol levels and blood glucose levels of trouts were >4-200 µg/L and >5 mmol/L under stress conditions, respectively. Plasma cortisol levels of the fish which were transported were from 5.0 5.0 µg/dL to 9.9 µg/dL. and the results of the control fish were 0.5 µg/dL. In conclusions, plasma cortisol levels of the transported fish were higher than the control fish group. These results may be indicator that the transported fish were under the stress; however, blood glucose levels of both control and transported fish were not indicated stress conditions.

Abreu J. S. de, A. I. Sanabria-Ochoa, F. O. Gonçalues, and E. C. Urbinati. 2008. Stress responses of juvenile matrinxă (Brycon amazonicus) after transport in a closed system under different loading densities. Ciĕncia Rural, Santa Maria, 38: 1413-1417.

Iwama K. G., 2004. Stress in fish. Fish Biol. Fisheries. 8: 35-36.

Tapia P.J., M. C. Puebla, and A. Muňoz, E. Rojas, C. M. Marchant, M. A. Cornejo, and M. Futagawa. 2012. Evaluation of the cortisol stres response in a marine perciform fish, the San pedro Oplegnathus insignis. North American Journal of Aquaculture, 74: 438-442.