ABSTRACT:These experiments were performed to determine the effects of dietary β-glucan on stress responses of striped catfish (Pangasianodon hypophthalmus). Fish were fed for nine weeks with a diet containing 0 (control), 0.5% (G1), 1% (G2) and 2% (G3 group) β-glucan. Subsequently, stress responses were studied by evaluating serum cortisol and glucose levels following a constant 24 h cold shock (from 28 °C to 15 °C). Serum cortisol and glucose concentrations were measured after cold treatments of varying durations (prior to, and after one, 12 and 24 h of cold shock stress, respectively). No differences in serum cortisol and glucose levels were found between control and β-glucan-treated fish. However, the mortality rate was significantly lowered in cold challenged fish fed appropriate doses of β-glucan (in G1 and G2 vs. G3 and control group). The results of the present study demonstrate that a proper administration of β-glucan in the diet could ameliorate the detrimental effects of a severe stress resulting in a reduction in fish mortality.

Cold-shock stress happens when a fish had been adjusted to a specific water temperature or range of temperatures and is consequently exposed to a rapid drop in temperature, resulting in a cascade of physiological and behavioral responses and, in some cases, death. In the current study, the stress response of striped Catfish (Pangasianodon hypophthalmus) was studied by evaluating serum cortisol and glucose level following an abrupt reduction in water temperature (from 28°C to 15°C) at different time points (prior to, and after 1h, 12h and 24h cold treatment, respectively). Regardless of some mortality occurred in cold challenged fish, none of the physiological parameters changed during evaluation period. The results, suggesting that despite of necessity of cortisol and glucose evaluation in any of stress assessment, yet, due to their high variability in different fish species, additional complementary tests such as measurement of other stress hormones e.g. heat shock proteins as well as blood-cell counts (preferably in chronic experiments) should also be included.