Research Article Stocking Density Induced Stress on Plasma Cortisol and Whole Blood Glucose Concentration in Nile Tilapia Fish (Oreochromis niloticus) of Lake Victoria, Kenya Elija Odhiambo , 1 Paul O. Angienda, 1 Patrick Okoth , 2 and David Onyango 1 1 Department of Zoology, Maseno University, Kisumu, Kenya 2 Department of Biological Sciences, School of Natural Sciences, Masinde Muliro University of Science and Technology, Kakamega, Kenya Correspondence should be addressed to Elija Odhiambo; elija.odhiambo@gmail.com Received 16 November 2019; Revised 16 April 2020; Accepted 19 June 2020; Published 17 July 2020 Academic Editor: Jo o Pedro Barreiros Copyright © 2020 Elija Odhiambo et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 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 > F crit � 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. e 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. e 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. 1. Introduction Fish and fisheries play an important role in addressing nutritional and livelihood food security, especially of the poor in the developing countries [1]. Globally over 2 billion people get at least 20% of their animal protein intake from fish [2, 3]. Nile tilapia (Oreochromis niloticus)are among the most important warm water fishes used for aquaculture production [4] and only the second most popular farmed fishes after Carps [3, 5, 6]. ey are recognized as one of the most important species in tropical and subtropical aqua- culture [2, 5, 7]. Nile tilapia have a mild white flesh that appeals to customers, making them economically important fish [8] and the most desired by Lake Victoria Community [9]. It is also an important fish model for studies on social stress due to overcrowding [10]. Stocking density is considered a key factor in deter- mining the productivity of fish aquaculture systems [11]. Crowding is judged as one of the most influential stressors affecting fish physiology and, thus, the status of well-being in aquaculture [12], and it is a common husbandry practice in aquaculture [13, 14]. High stocking density negatively affects both fish growth and feed utilization [1, 15]. High stocking densities have been shown to reduce feeding activity and growth rates in Coho Salmon (Oncorhynchus kisutch) and rainbow trout (Oncorhynchus mykiss) but have a positive Hindawi International Journal of Zoology Volume 2020, Article ID 9395268, 8 pages https://doi.org/10.1155/2020/9395268