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Carbohydrate Utilization and Digestibility by Tilapia, Oreochromis niloticus x O. aureus, Are Affected by Chromic Oxide Inclusion in the Diet^1,2,3,

Department of Marine Food Science, National Taiwan Ocean University, Keelung, Taiwan 202, Republic of China

A 12-wk feeding trial was conducted to study the influence of chromic oxide (Cr₂O₃) on carbohydrate utilization and digestibility by tilapia, Oreochromis niloticus x O. aureus. Two levels of chromic oxide (0.5 and 2%) were each incorporated into diets containing glucose or starch. Chromic oxide was added at 0 or 8 wk. The diets were fed to triplicate groups of fish weighing 1.11 ± 0.05 g. Fish fed the starch diet had greater (P < 0.05) weight gain, feed efficiency ratio, protein efficiency ratio, protein deposition and digestibility of protein, lipid, carbohydrate and dry matter than fish fed the glucose diet irrespective of the time and level of chromic oxide supplementation. Fish fed the glucose diet with 0.5% chromic oxide had higher weight gain, feed efficiency ratio, protein efficiency ratio and protein deposition than fish fed the glucose diet with 2% chromic oxide. The ingredient digestibility estimated using 0.5% chromic oxide as the marker was greater than that estimated with 2% chromic oxide. Higher phosphofructokinase and lower glucose-6-phosphatase activity was found in fish fed the starch diet than in fish fed the glucose diet regardless of the time and level of chromic oxide inclusion. Fish fed the glucose diet with 0.5% chromic oxide had higher phosphofructokinase activity and lower tissue chromium concentration than fish fed the glucose diet with 2% chromic oxide irrespective of chromic oxide inclusion time. These data suggest that the level of chromic oxide in the diet alters glucose utilization by tilapia and affects nutrient digestibility by tilapia. The time of chromic oxide inclusion had no effect on carbohydrate utilization and digestibility.

KEY WORDS: • carbohydrate • fish • tilapia • chromic oxide • digestibility

¹ Presented in part at the EIFAC Workshop on Methodology for Determination of Nutrient Requirements in Fish, June 29–July 1, 1993, Eichenau, Germany [Shiau, S. Y. & Liang, H. S. (1993) Effects of chromic oxide in diet as the apparent digestibility measuring index on carbohydrate utilization in tilapia. Proceedings of EIFAC Workshop (abs.)].

² Supported by a grant from the National Science Council of the Republic of China, grant number NSC 82-0409-B019-04.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence and reprint requests should be addressed.

Manuscript received 24 May 1994. Revision accepted 25 August 1994.