School of Natural Resources and Environmental Studies

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Author: search.filters.author.Opiyo, Mary A.

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    Spawning interactions between hatchery-reared and wild naturalized rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) in high-altitude tropical streams, Kenya
    (Wiley, 2022-07) Njue, Justus N.; Ngugi, Charles C.; Mucai, Muchiri; Opiyo, Mary A.
    Rainbow trout (Oncorhynchus mykiss) is among the most widely translocated fish species in the world. The current study evaluated the spawning interactions between naturalized and wild rainbow trout from two high-altitude second-order streams, in Kenya. Data on total length, weight, condition factor, fecundity, fertilization, egg diameter and fry survival were collected on spawning rainbow trout between March and December 2021. Length–weight relationship showed parabolic equations as W = 0.0144L2.900, W = 0.0069L3.0285 and W = 0.00027L3.175 for wild fish stock, hatcheryreared and wild × hatchery-reared rainbow trout, respectively. Total fecundity differed significantly among the hatchery-reared, wild fish and the cross of the two (p < 0.05). The fertilization rate showed significant differences (p < 0.05), with no discernable difference observed between the hatchery-reared and crossed (wild × hatchery-reared). There was a positive correlation among the total fecundity to female egg weight, female body weight, fertilization rate and eyed egg survival in all the populations. Relative fecundity was significantly different among the three groups of fish (p < 0.05), but the differences between the hatchery and the crossed (wild × hatchery-reared) fish showed no significant differences. We recommend the use of crossed (wild × hatchery-reared) populations for fry production for use in aqua-culture as they presented the highest fecundity and gave the best outcome of fry with high survival.
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    Different levels of probiotics affect growth, survival and body composition of Nile tilapia (Oreochromis niloticus) cultured in low input ponds
    (Elsevier, 2019) Ngugi, Charles C.; Karisa, Harrison Charo; Jumbe, James; Opiyo, Mary A.
    A 7-month experiment was carried out to determine the effects of different levels of probiotics (baker’s yeast (Saccharomyces cerevisiae) and Bacillus subtilis) on Nile tilapia (Oreochromis niloticus) reared in low input ponds. Monosex male fingerlings (40 g) were randomly distributed into 28, 1.25 m3 net cages at 50 fish m−3 and 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: Diet 0 (control); Diet 1–3 were supplemented with S. cerevisiae at 2 g kg −1 (Diet 1); 4 g kg−1 (Diet 2) and 6 g kg −1 (Diet 3) whereas Diet 4–6 were supplemented with B. subtilis at 5 g kg−1 (Diet 4); 10 g kg−1 (Diet 5) and 15 g kg−1 (Diet 6). Higher final weight (255.31 ± 3.19), Specific Growth rates (SGR) (0.77±0.01) and better Feed Conversion Ratio (FCR) (1.61 ± 0.02) were recorded in fish fed on Diet 2 followed by fish fed on Diet 5. Fish fed on probiotic- supplemented diets had significantly better growth, nutrient utilization and FCR compared to fish fed on the control diet (P < 0.05). Probiotic supplementation significantly affected the body composition of the fish (P < 0.05). S. cerevisiae led to significantly high protein (86.06%) at 4 g kg−1 (Diet 2) (P < 0.05) while B. subtilis led to significantly higher protein (89.40%) at 5 g kg−1 (Diet 4) (P < 0.05). Crude lipid and ash content were significantly lower in the fish fed on probiotic supplemented diets (P < 0.05) compared to the control. This study has demonstrated that the application of probiotics in diets of Nile tilapia in low input ponds promotes growth and enhances body composition. The two probiotics have got different effects depending on the level of application. S. cerevisiae exhibited the best performance at 4 g kg−1 while B. subtilis had the best performance at 10 g kg−1
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    Dietary administration of probiotics modulates non-specific immunity and gut microbiota of Nile tilapia (Oreochromis niloticus) cultured in low input ponds
    (International Journal of Veterinary Science and Medicine, 2019) Ngugi, Charles C.; Jumbe, James; Opiyo, Mary A.; Charo-Karisa, Harrison
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