Expression of Plasma Glucose Transporter Protein 1 (Glut 1) Induced by Chronic Stress in Nile Tilapia (Oreochromis Niloticus Linnaeus 1758) Reared at High Stocking Density

Abstract

High stocking density (HSD) has been found suitable to overcome the problem of land shortage, and it has the desirable effect of increasing fish production hence a potential profit , maker. However, HSD isa chronic stressor that reduces growth 0 rates; increases immunosuppression and susceptibility to diseases; and may lead to stock loss. HSD is likely to lower profitability of fish farming if not implemented properly. Stress elevates plasma cortisol levels, which in turn promotes carbohydrate metabolism leading to high blood glucose levels. Glucose, the cellular biofuel, is transported to various tissues by glucose transporter protein (GLUTs) in order to maintain normalcy. GLUT 1 is located in erythrocyte membrane and has high preference for glucose, and is thus responsible for transport of glucose in Erythrocytes. However, knowledge about how glucose relates to GLUT 1 protein in fish subjected to HSD is still unclear. Therefore, this study examined the effect of HSD on the plasma levels of GLUT 1 protein in Nile tilapia. Fish were reared for 28 days at l.5 kg/ m3 and 4.5 kg/m ' for low stocking density (LSD) and HSD respectively. Cortisol levels were measured by competitive ELISA. Blood glucose level, haemoglobin concentration (Hb), and haematocrit (Hct) were also measured. Erythrocytes count and differential leukocyte count were determined by haemocytometer. GLUT 1 levels were determined by SDS-PAGE and Western blot. HSD fish had high cortisol level, glucose level, Hb, Hct, erthrocyte count, neutrophils, and Monocytes (p < 0.05). HSD individuals had lower lymphocyte numbers compared to LSD individuals (p < 0.05). Significantly higher GLUT 1 levels were detected . - in HSD individuals ( x±SEM = 2.0±O.22) compared to LSD individuals ( x±SEM = O.25±O.06), p < 0.05. This data point to the fact that HSD induces chronic stress that interferes with the normal physiology of fish. The result from this study also shows that HSD heightens expression of GLUT 1 protein in blood, and as such the level of GLUT 1 can be used as a stress indicator in fish farming.