Stocking Density Induced Stress on Plasma Cortisol and Whole Blood Glucose Concentration in Nile Tilapia Fish (Oreochromis niloticus) of Lake Victoria, Kenya

Abstract

Effects of high stocking densities (HSDs) were evaluated for Nile tilapia fish (Oreochromis niloticus) under culture to determine its influence on plasma cortisol and whole blood glucose concentration. Plasma cortisol levels (ng/ml) were assayed by Enzyme-Linked Immunosorbent Assay (ELISA). Whole blood glucose levels were determined using a hand-held one touch ultraglucose meter (MD-300) and test strips. Plasma cortisol and whole blood glucose level determinations were replicated three times for O. niloticus reared under both low stocking densities (LSD) and HSD. One way Analysis of Variance (ANOVA) was performed on the data collected, and comparison of significant differences in means was carried out between LSD and HSD at 0.01%. Plasma cortisol levels revealed statistically (P≤0.01) significant values of HSD at 6.32 ± 1.06 ng/ml than in LSD at 4.62 ± 1.58 ng/ml for the O. niloticus groups studied. Whole blood glucose analysis revealed a statistical (P<0.05) difference in the means in HSD and LSD O. niloticus groups (F(df,1; 8) = 7.946 > Fcrit = 4.414; P=0.01). Mean plasma glucose concentration was statistically (P≤0.01) higher for HSD than LSD O. niloticus groups at mean ± SD, 96.84 ± 5.28 and 76.82 ± 5.92, respectively. The findings of this study demonstrate that high stocking densities increase both cortisol and whole blood glucose concentration in tilapia fish, indicating a marked increase in stress levels. Elevated plasma cortisol and whole blood glucose concentration can be used as biomarkers for acute stress in O. niloticus produced under aquaculture systems. The findings of this study can help inform policy on the management of stress caused by overstocking of O. niloticus and other related Cichlids under industrial aquaculture production.

Effects of Garlic Allium sativum Powder on Nutrient Digestibility, Haematology, and Immune and Stress Responses in Eurasian Perch Perca fluviatilis Juveniles

“…At 1, 6, and 24 h post-stress, blood serum cortisol was lower in all of the garlic groups compared to the levels in the control grpi. High-density stocking [ 95 ], handling [ 27 ], heat stress [ 96 ], and low water pH [ 66 ] have been reported to increase levels of cortisol and glucose in fish. The inclusion of 2 mg nano selenium and 2 ppm garlic extract reduced blood plasma cortisol and glucose in grass carp ( Ctenopharyngodon idella ) under stocking density stress [ 97 ], while 200 ppm of a mixture of garlic and labiatae essential oil (Delacon, Austria) (PHYTO diet) reduced blood serum cortisol after 2 h overcrowding stress but did not show any effect on blood glucose ( p > 0.05) in European sea bass [ 84 ].…”

Haematological and serum biochemical reference values of snow trout, Schizothorax labiatus habiting in river Sindh of Indian Himalayan region

“…Most pathological alterations mainly appear in the serum before the occurrence of any disease and hence can be used as disease‐diagnosing techniques (Tripathi, 2003). Serum glucose, cholesterol, urea, uric acid and protein contents act as indicators of nutritional status (Garcia‐Rodriguez et al ., 1987) and glucose is believed to perform a significant role during secondary stress in fishes (Barton & Iwama, 1991; Odhiambo et al ., 2020). A significant alteration in the level of serum biochemical parameters has been reported by many workers in the past and suggested that the values of glucose, serum protein, albumin, globulin and enzymatic activities in the blood plasma are designated as specific indicators of sympathetic activation during stress conditions (Adham et al ., 1997; Lermen et al ., 2004; Santos & Pacheco, 1996; Svobodova et al ., 2001; Velisek et al ., 2009).…”

An Assessment of the Risk Factors Associated with Disease Outbreaks across Tilapia Farms in Central and Southern Zambia

“…This result is in contrast to studies that have demonstrated that fish reared in high stocking densities (>8 fish/m 2 ) are susceptible to high mortalities. High stocking densities have been shown to reduce feeding activity and growth rates in farmed fish as well as increase the level of metabolites, such as urine and faeces, in pond water [30]. Accumulating metabolites change water quality, subjecting fish to chemical stressors in addition to the chronic stress caused by social dominance [31,32].…”