Abdelghany, A.E.
Abstract:
Purified diets were formulated and fed to seven groups of Nile tilapia, Oreochromis niloticus fingerlings for 12 weeks. Six of the formulated diets contained 5 or 50 mg/kg of ascorbic acid equivalent supplied either by L-ascorbic acid (AA), L-ascorbyl-2-sulfate (AS) or L-ascorbyl-2-polyphosphate (APP). The seventh basal diet was ascorbate-free and served as the control. The results demonstrated that feed efficiency and growth parameters of fish fed diets APP5, AS5, AA5 or AA50 were statistically similar to the same parameters of the control diet. The study indicated that diets supplemented with 5 or 50 mg/kg of ascorbic acid in the form of APP or AS were more effectively utilized as sources of vitamin C than equimolar AA in promoting growth, improving food efficiency, increasing nutrients retention and preventing scurvy in Nile tilapia. Fish fed the ascorbate-free diet and the diet containing 5 mg AA/kg exhibited external signs of scurvy at the last growth period of the experiment. Diets containing 5 mg/kg of ascorbic acid from AS or APP provided some growth with no overt signs of scurvy indicating that this concentration of AS and APP might be near the minimum requirements for the species. Diet supplemented with 50 mg ascorbic acid equivalent from APP/kg was the most efficient diet having significantly (P<0.05) the lowest value of the amount of dietary protein necessary for 100 g weight gain (DPI), the highest values of feed efficiency ratio (FER), and the highest values of nutrients retention (of protein (PRV), fat (FRV), ash (ARV) and gross energy (ERV)) among the other diets. Fish received that diet (APP50) had significantly (P<0.05) the highest weight gain and protein gain in tissues among the other fish groups. The increase in feed efficiency and growth parameter values of fish received diet APP50 over the values of same parameters of diet AA50 were calculated as percentages and the results were as follows: 36.2% for weight gain, 40.9 for protein gain, 53.3% for FER, 58.1% for PRV, 34.9% for FRV, 57.4% for ARV and 51.9% for ERV. Diet containing 50 mg APP/kg was followed in order by diet supplemented with 50 mg ascorbic acid equivalent from AS/kg. Diet AS50 had statistically comparable (P>0.05) values of weight gain, protein gain and FRV to same parameters of APP50 diet. The increase feed efficiency and growth parameters values of fish received diet AS50 over the values of same parameters of diet AA50 were calculated as percentages and the results were as follow: 27.9% for weight gain, 27.9% for protein gain, 18.2% for FER, 17.9% for PRV, 19.2 for FRV, 8.9% for ARV and 18.2 ERV. The percentages of moisture, protein, and ash in whole fish at the end of the study had no significant (P>0.05) differences between groups whereas lipid percentages were significantly (P<0.05) lower in all the tested groups comparing to that of the control fish group. Increasing the level of ascorbic acid equivalent from 5 mg to 50 mg/kg diet from APP, AS or AA reduced the percent fat in Nile tilapia bodies. These results indicate that all the tested vitamin C sources were effective in inducing lipolysis in Nile tilapia tissues.
(Central Laboratory of Aquaculture Research, Abbassa, Abohamad, Sharkia, Egypt)
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