EFFECTS OF PROBIOTICS ON GROWTH, FLESH QUALITY AND HEMATOIMMUNOLOGICAL STATUS OF CULTURED NILE TILAPIA (Oreochromis niloticus) IN KIRINYAGA COUNTY, KENYA
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Date
2026-08
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Abstract
Nile tilapia (Oreochromis niloticus) culture in Kenya is mainly conducted in low input
ponds where supplementary feed is given alongside pond fertilization. Excess nutrients in
the culture water in form of nitrogen (N) and phosphorus (P) may make the culture
environment susceptible to invasion by disease-causing microorganisms. In the recent past,
probiotics have received much attention as a new strategy in fish health management and
have been documented to improve fish growth performance and immunity in fish cultured
in recirculating systems. However, their effect in tilapia cultured in low input ponds is still
relatively unknown. In this study, monosex O. niloticus fingerlings with a mean weight of
39.75 ± 0.05 g were randomly stocked at 50 fish m-3 in 1.25 m3 cages in low input earthen
ponds. The fish were fed twice daily at 3% body weight on seven isonitrogenous (28%
crude protein) diets supplemented with either Saccharomyces cerevisiae (1×1010 CFU g-1)
or Bacillus subtilis (1×109
CFU g-1) at different levels as follows: No probiotic (Diet 0); S.
cerevisiae at 2 g kg−1 (Diet 1), 4 g kg−1 (Diet 2) and 6 g kg−1 (Diet 3); and B. subtilis at 5 g
kg−1 (Diet 4), 10 g kg−1 (Diet 5) and 15 g kg−1 (Diet 6) for a period of 7 months. The fish
were sampled monthly for weight and length measurements. Hemato-immunological
parameters were determined by blood sampling and hematological analysis for red blood
cells, white blood cell and haemoglobin counts. Blood serum assay was conducted using
commercial enzyme-linked immunosorbent assay (ELISA) kits to determine the serum
protein, albumin, globulin levels and lysozyme activity. Microbiological samples were
analyzed through sub-culturing to obtain pure cultures on nutrient media and enumerated
through standard methods. Results of the trials indicated that the highest performance was
achieved with Diet 2. The highest final weight (255.31 ± 3.19 g), Specific growth rates
(SGR) (0.77±0.01% day-1) and feed conversion ratio (FCR) (1.61 ± 0.02) were recorded in
fish fed Diet 2. This was followed by fish fed Diet 5. Results of growth performance
analysis indicated that fish fed on probiotic-supplemented diets had significantly better
growth, nutrient utilization and FCR than fish fed on the control diet (P < 0.05). Probiotic
supplementation significantly affected the body composition of the fish (P < 0.05).
Saccharomyces cerevisiae at 4 g kg-1 (Diet 2) led to significantly high protein (86.06%) (P
< 0.05) while B. subtilis at 5 g kg-1 (Diet 4) led to significantly higher protein (89.40%) (P
< 0.05). Crude lipid and ash content were significantly lower in the fish fed probioticsupplemented diets (P < 0.05) compared to the control. Results of hemato-immunological
analysis indicated that haemoglobin (Hb), red blood cells (RBC), white blood cells (WBC),
serum protein, albumin, globulin and lysozyme activity were higher in fish fed on
probiotic-supplemented diets and lower in the control group (Diet 0). Probiotic
significantly affected hemato-immunological parameters (P < 0.05). Fish fed on probioticsupplemented diets retained the probiotics in their guts and had lower microbial load in
their muscle (P < 0.05). This study shows that incorporation of probiotics in diets of Nile
tilapia in low input ponds promotes growth performance, enhances body composition,
improves immunity and manipulates gut microbiota of fish. The two probiotics differ in
effect at different levels of application. Probiotic S. cerevisiae exhibited the best
performance at 4 g kg-1 while B. subtilis had the best performance at 10 g kg-1. Probiotics
are therefore recommended for use in low input fish culture systems for better nutrient
utilization, higher yields and improved fish health for increased aquaculture production.