HEMATOLOGICAL AND BIOCHEMICAL PARAMETERS AS ALTERNATIVE MARKERS OF STOCKING DENSITY- INDUCED STRESS IN CULTURED NILE TILAPIA, (Oreochromis niloticus Linnaeus, 1758) UNDER CULTURE CONDITIONS.

Abstract

Fish and fisheries play a significant role in meeting nutritional food security, more so of the poor communities in the low and middle income countries (LMIC).Oreochromis niloticusisone the most valuable warm water fishes used in aquaculture systems. Various stressors trigger specific stress responses in O. niloticus. High stocking density (HSD) causes persistent stress response, which brings about inhibited fish breeding, growth, and decreased immune capacity thus decreased yield. Studies have been done in other regions of the world to evaluate the various hematological and biochemical parameters in O. niloticus as markers of stress, thus this study evaluated four specific parameters and to customize them for use by O. niloticus farmers in the Counties boardering Lake Victoria in Kenya. Two specific objectives were evaluated in this study namely; to determine the relative hematological parameter; erythrocyte count in cultured O. niloticus, subjected to stocking density induced stress and to determine the relative biochemical parameters; plasma cortisol, whole blood glucose, and blood electrolytes concentrations in cultured O. niloticus, subjected to stocking density induced stress. Stocking rates for the aquaria was done by matching all the fish for body weight/standard mass, Mean± SD (15 ± 1 g) thus, 150 g and 300 g of body weight/ 0.05 m3aquarium for low stocking density (LSD) and HSD respectively both in triplicates. The fish were cultured for 21 days following 3 days of acclimatization to the laboratory conditions after being obtained from the University`s fish rearing facility by seining technique. The fish were fed on a carbohydrate based feed of chick mash at 18 % protein supplemented with crushed Rastrineobola argentea to 25 % protein at a feed portion of 10 g/kg of life body weight. Blood samples were drawn using cardiac puncture technique from fish anaestethised with 2 – phenoxyethanol at 0.30 ml.l-1 from each aquarium (n = 5) using a large sieve. Erythrocyte counts (n = 18) were assayed for using hemocytometer. Plasma cortisol concentration (ng/ml) (n =18) levels were assayed for by use of Enzyme-Linked Immunosorbent Assay. Whole blood glucose concentration levels (n = 30) were determined using a hand-held One Touch Ultra glucose meter (MD-300) and test strips. Electrolyte concentrations (n =18) were assayed using Sherwood Flame Photometer 410. Whole blood glucose analysis revealed statistical (P< 0.05) difference in the means in HSD and LSD O. niloticus groups. Mean plasma glucose concentration was statistically significantly (P ≤ 0.01) higher for HSD than LSD O. niloticus groups at mean ± SD, 96.84 ± 5.28mgd-1 and 76.80 ± 5.92 mgd-1respectively. One-way Analysis of Variance (ANOVA) was done on the data collected and comparison of significant differences in means done between LSD and HSD at 0.01%. Plasma cortisol levels revealed statistically (P ≤ 0.01) significant values of HSD at mean ± SD, 6.35 ± 0.89ng/ml and 4.49 ± 1.08 ng/ml respectively. One way ANOVA analysis of the true electrolyte means for the LSD and HSDO. niloticus groups revealed significantly (P ˂ 0.05) higher mean at mean ± SD (1.63 ± 0.18 mmol/l) HSD and (1.11 ± 0.08 mmol/l)LSD for Na+, (0.73 ± 0.03 mmol/l)HSD and (0.42 ± 0.02 mmol/l)LSD for K+ with no statistical (P˂ 0.05) difference at mean ± SD (0.13 ± 0.00)HSD and (0.13 ± 0.00)LSD for Ca++.One-Way ANOVA analysis revealed significant (P ˂ 0.05) difference in the erythrocyte count means in LSD and HSD O. niloticus groups at mean ± SD, 7.01 ± 0.77 x 106 mm-3 and 3.36 ± 0.63 x 106 mm-3 respectively. Overally, the findings of this study demonstrate that high HSD increase erythrocyte count, plasma cortisol, whole blood glucose, and Na+ and K+ concentration in O. niloticus fish indicating a marked increase in stress levels. Elevated erythrocyte count, plasma cortisol, whole blood glucose, and Na+ and K+ concentrations can be used as alternative biomarkers for acute stress in O. niloticus produced under aquaculture systems. The findings of this study can help improve aquaculture practices on management of chronic stress in O. niloticus and related Cichlids under industrial aquaculture production through timely diagnosis and deployment of appropriate mitigation measures.