Interactive effects of dietary protein and live bakery yeast, Saccharomyces cerevisiae on growth performance of Nile tilapia, Oreochromis niloticus (L.) fry and their challenge against Aeromonas hydrophila infection |
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| Authors: | Mohsen Abdel-Tawwab |
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| Institution: | (1) Department of Fish Biology and Ecology, Central Laboratory for Aquaculture Research, Abbassa, Abo-Hammad, Sharqia, 44662, Egypt |
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| Abstract: | Yeasts used as a probiotic in fish diets could stimulate fish resistance against bacterial infection and could enhance the
activities of digestive enzymes in fish guts. In addition to yeast importance, dietary protein is another important part in
fish diets that should be carefully optimized to meet fish requirement. It is proposed that the yeast supplementation may
enhance the dietary protein turnover and reduce the protein requirement for fish. Therefore, the interactive effects of dietary
protein and yeast levels on the growth performance of Nile tilapia, Oreochromis niloticus (L.) fry and their challenge against Aeromonas hydrophila infection was evaluated. In the present study, ten experimental diets were formulated to contain either 35% or 45% crude
protein (CP). For each protein level treatment, bakery yeast (Saccharomyces cerevisiae) was supplemented at 0.0, 0.50, 1.0, 2.0, or 5.0 g/kg diet. Fish (0.25–0.48 g) were distributed at a rate of 25 fish per
140-L aquarium. For each diet, triplicate aquaria were fed twice a day, 5 days a week for 12 weeks. Fish growth and feed utilization
were significantly affected by either dietary protein or yeast levels alone, while no significant effect of their interaction
was observed. The highest fish growth was obtained at 1.0–5.0 g yeast/kg diet at both protein levels; however, the fish performance
at 45% CP was better than that fed on 35% CP diets. The optimum feed conversion ratio (FCR) was obtained when fish fed on
1.0–5.0 and 2.0–5.0 g yeast/kg diet at 35 and 45% CP, respectively. The cumulative fish mortality, after interperitoneal injection
with A. hydrophila for 10 days, and bactericidal activity was significantly higher in fish fed 35% CP diets than those fed 45% CP diets. Both
variables decreased significantly with the increase in yeast levels. The lowest bacterial count and bactericidal activity
were obtained in fish fed 5.0 g yeast/kg diet irrespective to dietary protein levels. It could be concluded that the inclusion
of live bakery yeast in practical diets could improve the growth performances, feed utilization, and physiological status
of Nile tilapia fry and their challenge against A. hydrophila infection. Moreover, fish performance when fed 45% CP diet was better than those fed 35% CP diet. Based on these results,
the most suitable yeast level for maximum Nile tilapia growth was determined to be 2.0 g yeast/kg diet with 45% CP diet; however,
this level was recommended to stimulate their productive performance and enhances their resistance against A. hydrophila infection. |
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