The composition of Zostera capricorni seeds: a seasonal natural food of juvenile Penaeus esculentus Haswell (Penaeidae: Decapoda)

Abstract

Seeds of Zostera capricorni, which are selectively eaten by Penaeus esculentus during the November-December fruiting period, contained 10% protein, 3% lipid and 60% digestible carbohydrate (dry weight), the remainder being fibre and ash. The protein was characterised by a high proportion of arginine (29%), but its composition was otherwise unexceptional. Neutral lipids comprised 82% of total lipid, mostly as sterol, sterol ester, diacylglycerol and triacylglycerol; phosphatidylinositol was the principal phospholipid (14%), followed by phosphatidylethanolamine (4%) and phosphatidylcholine (<2%). There was a range of saturated fatty acids from C 14 to C 24, but most were C 16 and C 18. Nearly all the monounsaturated fatty acid was C18:1 n − 9, and only C 18 polyunsaturated fatty acids were detected. Most of the pigment was chlorophyll a or b, but 20 μg/g was carotenoid. A natural food budget was calculated, incorporating prey animals and Zostera in the proportions normally eaten. Total ash-free protein was 66%, lipid 13% and carbohydrate 21%; without the Zostera seeds the carbohydrate was only 11%. The seeds appear to be selected because they exude some attractant and are readily available in quantity. The main nutritional benefit appears to be in their energy content, although they may contain some unidentified beneficial component found only in plants.