Nile tilapia, Oreochromis niloticus (average initial weight, 5.91 ± 0.04 g), were fed
four isonitrogenous and isolipidic diets for 84 days. The diets contained four levels of
yeast extract (CW-I)
rich in nucleotides and β-glucan:
0 (control), 5, 10 and 15 g/kg
diet. Weight gain increased linearly, whereas the feed conversion ratio decreased
linearly with increasing levels of yeast extract. The diet containing 15 g/kg yeast extract
resulted in significantly better (p < 0.05) specific growth rates and protein efficiency
ratios. No significant (p > 0.05) differences were found in dry matter, protein,
lipid or ash contents or in haematocrit, haemoglobin or total protein contents among
the treatment groups. Blood sample profiles showed an increase in white and red
blood cells in fish fed 15 g/kg yeast extract in comparison with the other treatment
groups. The fish fed the diets with 10 and 15 g/kg yeast extract had significantly
higher albumin and globulin levels than the control group, whereas decreased levels
of cholesterol and triglycerides, aspartate aminotransferase and alanine aminotransferase
were noted in fish fed the diet with 15 g/kg yeast extract. Histological analysis
of the liver and intestine in fish fed the control diet showed a slightly abnormal structure
in these organs. Only in fish fed diets supplemented with the highest amount of
yeast extract was the structure of the hepatocytes and villi almost unchanged, which
indicated that the yeast nucleotides could improve hepatic function and promote
liver and gut restoration.