Changes in the Condition Index and Chemical Contents of Venerupis (decussata decussate L.) from the Egyptian Coastal Waters.

Abstract

Changes in the condition index and chemical contents of adult and young aged exotic Manila Venerupis (decussata decussata L.) have been studied. Animals were collected monthly from El-Mex Bay during the period from April 1993 to April 1994. Monthly variations in total lipid, phospholipid, triglyceride, free fatty acids (FFA), phosphorus, potassium and magnesium were determined in animals of different sizes. Their average values being; 20.93%, 10.54%, 1.04%, 1.26%, 4.23 mg/g, 3.26 mg/g and 1.71 mg/g dry weight for the corresponding parameters respectively. Mostly, there was a fall in the condition index associated with considerable rise in total lipid and their constituents (Phospholipid, FFA and triglycerides). Venerupis tissues are of extremly high lipid and relatively high phospholipids, it constitutes about 49% of the roe lipid comparing to about 6% FFA and 5% triglycerides and consequently low cholestrol content. It has very low Iodine value, mostly within the average of 27.8 to 31.85, and is characterized by low density and low unsaturated lipids.

Fluctuations in the lipid content of the animals followed the relative change in food intake throughout the year and the state of maturation. A marked reduction in lipid and some of its constituents was associated with lowering temperature in winter, as the result of the reduction in feeding activity. The major period of spawning occurred from June through September, and is accompanied by lipid metabolism.

P and K were found to promote the growth rate and increased with increasing the condition index and showed high bioaccumulation rate, in contrast to Mg.