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This study assessed the physical characteristics, faecal, ammonia and phosphorus waste production rates of mixtures of groundnut, cottonseed, copra and soybean meals as a replacement for fishmeal in Nile tilapia diets. Six experimental diets were formulated such that the oilseed mixtures contributed 80% of total dietary protein. A fishmeal-based diet served as the control. The diets were randomly assigned in triplicates to the experimental tanks, containing 15 juvenile tilapia with a bulk weight of ~1 kg. Ammonia and phosphorus excretion rates of the diets were monitored at 3-hour intervals over 24 h. The pellet characteristics, faecal and nutrient waste production were assessed. The control diet recorded a mean bulk density of 376.00 ±5.19 g L-1 which was lower than the oilseed-based diets which ranged from 550.67 ± 3.06 g L-1 to 614.27 ± 2.08 g L-1. There was a positive correlation (p < 0. 0001; r = 0.93) between the sinking rates of pellets and their bulk densities. The oilseed-based diets recorded 4-45% higher faecal matter production compared to the control diet. Fish fed Diet 3 had the lowest Total Ammonia-nitrogen (TAN) excretion rate of 106.14±1.95 mg kg-1 while the control diet recorded the highest TAN excretion of 162.31 ±4.39 mg kg-1. Accumulated dissolved phosphorus was 64.52-74.09% lower in the oilseed-based diets compared to the control. [ABSTRACT FROM AUTHOR]

The yeast Saccharomyces cerevisiae is one of the commonest probiotics incorporated in aquafeeds. An 84-day feeding trial was conducted to evaluate the effects of varying dietary inclusions of S. cerevisiae, 0% (control), 3% (YF3), 5% (YF5), and 7% (YF7), on growth, stress tolerance, and disease resistance in juvenile (body mass ~ 21 g) Nile tilapia (Oreochromis niloticus). Fish were randomly distributed in groups of 20 into 12 1-m3 hapas and fed isoenergetic (~ 17 kJ g−1 gross energy) and isonitrogenous (~ 300 g kg−1 crude protein) diets at 3% of their bulk weight daily. Specific growth rates were significantly higher for the yeast-fed fish (0.77-0.78% day−1) than for the control fish (0.60% day−1) and resulted in significantly higher mean final weights for the yeast-treated groups. Protein and lipid retention efficiencies were also significantly higher in the yeast-fed fish than in the control group. In subsequent stress challenge trials, the yeast-fed fish had greater tolerance to acute heat as well as hypoxia exposure than the control fish. Survival rates of the yeast-treated groups following sudden exposure to elevated water temperature (40 °C) ranged from 82.5 to 100% compared to 15% for the control. Mean survival rates following a 24-h hypoxia exposure were also generally significantly higher for the yeast-fed fish. The probiotic groups recorded a relative percent survival (RPS) of 75% after a 14-day Aeromonas hydrophila infection challenge. The results of this study indicate that S. cerevisiae as an additive in Nile tilapia diets has beneficial impacts on growth, stress tolerance, and disease resistance. [ABSTRACT FROM AUTHOR]