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Two feeding experiments were conducted to assess the quantitative cholesterol requirement of the juvenile prawn, Penaeus japonicus. The prawns were fed casein‐based (experiment 1) and casein‐ or crab protein‐based (experiment 2) diets with or without supplemental cholesterol. The daily increases in quantities of body cholesterol (mg kg−1prawn day−1) at maximum growth and dietary cholesterol intake over a 40‐day feeding period were determined. Prawns fed 5 g kg−1supplemental cholesterol, regardless of protein sources, gave the highest weight gain. Body retention efficiencies of dietary cholesterol (cholesterol retained × 100/cholesterol intake) vary among prawns fed 5 g kg−1supplemental cholesterol (diets 3, 5 and 7) but dietary cholesterol requirements expressed as mg kg−1body weight (BW) day−1were not significantly different (180 to 200 mg kg−1BW day−1). Based on dietary cholesterol requirement, the optimum dietary cholesterol levels for the juvenile prawns were estimated in relation to feeding levels. When feeding levels were 3%, 5% and 7% of body weight, optimum dietary cholesterol levels were 5.0 to 6.0, 3.6 to 4.0, and 2.6 to 2.9 g kg−1of dry diet, respectively. The present study showed the advantages of determining daily cholesterol requirement (mg kg−1BW day−1) at maximum growth through a factorial method in determining optimum dietary cholesterol levels in P. japonicus.

The utilization of oleic acid as an energy source and the effects of oleic acid levels and/or dietary soy bean lecithin (SBL) on oleic acid utilization, growth and survival, and lipid class and fatty acid compositions of freshwater prawn, Macrobrachium rosenbergii(de Man), juveniles were determined.

An attempt was made to measure the apparent digestibility (AD) of cholesterol and fatty acids using 5aL‐cholestane as a marker (cholestane‐method) using tilapia. Oreochromis niloticus, and the freshwater prawn, Macrobrachium rosenbergii, as test animals. The results were compared with those obtained by the Cr2O3‐method. Casein‐based test diets containing 0.3% levels of cholestane and chromic oxide as markers were prepared for determination of AD of dietary cholesterol and fatty acids. After 2 weeks of acclimation, the test animals, tilapia (average 3.0 g wet weight) and freshwater prawn (average 0.5 g wet weight) were fed the test diets for 1 week, and faecal samples were collected over 6 subsequent days. Lipids in the diets and faeces were extracted with chloroform‐methanol and saponified with 10% KOH in methanol. Gas‐liquid chromatography (GLC) on 1.5% OV‐17 of the unsaponifiable matters afforded the quantities of 5aL‐cholestane and cholesterol, whereas that on 5% Shinchrom E‐71 of the saponifiable matters provided the quantities of fatty acids. Chromic oxide was determined by a wet‐digestion method. In tilapia, the AD of cholesterol determined by cholestane‐ and Cr2O3‐methods were 78.1% and 73.5%, respectively. The AD of individual fatty acids differed with the types of fatty acids, but those of fatty acids determined by the two methods in this study were similar, except for a slightly higher value of several fatty acids such as 16:1 in the cholestane‐method than in the Cr2O3‐method. This indicates that 5α‐cholestane as well as Cr2O3can be conventionally used as a marker for determining AD of fatty acids and cholesterol. The cholestane‐method is advantageous as it permits parallel analysis of cholesterol (or fatty acids) and 5α‐cholestane by GLC using small amounts of faecal sample. The cholestane‐method was also useful for analysing digestibilities of cholesterol and total lipids in freshwater prawn. However, slight differences between the cholestane‐ and Cr2O3‐methods were observed in the AD of several fatty acids such as 14:0 and 16:1.