Effect of stocking density on the expression of glucose transporter protein 1 and other physiological factors in the Lake Victoria Nile tilapia, Oreochromis niloticus (L.)

Abstract

Fish farmers have a tendency of employing high stocking density (HSD) as a means of increasing productivity. However, HSD is a chronic stressor that is likely to lower profitability of fish farming if not implemented properly. HSD induces stress which in turn elevates sequentially the levels of plasma cortisol and glucose. The resultant glucose is distributed to various tissues by glucose transporter protein (GLUTs) to restore normalcy. GLUT 1, transmembrane protein found in erythrocytes, is responsible for import and export of glucose in red blood cells. However, knowledge on how chronic stress impact glucose and GLUT 1 protein in fish subjected to HSD is still unclear. In this study, effect of HSD on the expression of GLUT 1 in Nile tilapia was investigated in an attempt to elucidate the role of GLUT 1 in glucose metabolism during chronic stress. Fish were reared for 4 weeks at 1.5 and 4.5 kg/m 3 for low stocking density (LSD) and HSD, respectively. Four physiological parameters were determined from the blood samples obtained from fish at the end of experiment. At p \ 0.05, there were significant differences between fish reared at HSD and LSD in plasma cortisol level (72.1 ± 5.9 ng/ml and 37.5 ± 4.6 ng/ml); blood glucose level (136.00 ± 1.3 mg/dL and 70.2 ± 1.0 mg/dL); erythrocytes count (7.2 ± 0.5 9 106 mm -3 and 2.1 ± 0.4 9 106 mm -3 ); and plasma GLUT 1 level (1.40 ± 0.17 rbi and 0.81 ± 0.07 rbi), respectively. HSD induced elevation of plasma cortisol level, blood glucose level, erythrocytes count and GLUT 1 level. These elevated physiological factors and particularly GLUT 1 can be used as a cellular stress biomarker in fish farming and aquaculture.

Establishment of a non-invasive method for stress evaluation in farmed salmon based on direct fecal corticoid metabolites measurement

“…A C C E P T E D ACCEPTED MANUSCRIPT 14 L.), Nile tilapia, white sturgeon (Acipenser transmontanus), and rainbow trout (Oncorhynchus mykiss) [28][29][30][31][32]. Hormone concentrations could be very different between species.…”

How Different Stocking Densities Affect Growth and Stress Status of Acipenser baerii Early Stage Larvae

“…GLUT1 is responsible for the import and export of glucose into red blood cells. The effect of high density has been studied in Nile tilapia, Oreochromis niloticus, demonstrating an increase in glut1 expression, which can be used as a cellular stress biomarker in aquaculture [28]. The glut2 gene codes for the sodium-independent glucose transporter (GLUT2), and a significant increase in the number of glut2 mRNA copies in response to acute and chronic hypoxia has been demonstrated in liver of European seabass, Dicentrachus labrax, by Terova et al [29].…”

Physiological stress biomarkers reveal stocking density effects in late larval Delta Smelt (Hypomesus transpacificus)

“…Commonly applied methods used in density studies include assessments of parameters involved in aquaculture production and nutritional status (mortality, body condition factor, food intake, food conversion rate, growth, and size variation), health condition (blood parameters, fin damage, gill condition, and spleen condition), as well as stress indicators (cortisol and glucose concentrations, and elevated oxygen consumption) (Ellis et al, 2002;North et al, 2006). Some endpoints, such as those involved in aquaculture production, nutritional status, health condition, and behavior can take longer to manifest and are thus predominantly applied to experiments lasting several weeks to months (Adams et al, 2007;Aketch et al, 2014;Alanärä and Brännäs, 1996;Boujard et al, 2002;Brown et al, 1992;de Oliveira et al, 2012). In contrast, other parameters involved in the immediate stress response, e.g., cortisol levels and gene expression, change rapidly and can be used to determine short term stress and stress recovery at time points ranging from several hours to a few days (Caipang et al, 2008a, b;Fast et al, 2008).…”

“…On the other hand, high stocking densities can also result in an increase in stress levels due to intraspecific competition. Studies on different species and different experimental settings have indicated that both high and low stocking densities can cause severe stress in fish (Aketch et al, 2014;Alanärä and Brännäs, 1996;Brown et al, 1992;Costas et al, 2008;Jørgensen et al, 1993).…”