Variations in gross biochemical composition, energy value and condition index of Tapes philippinarum from the Lagoon of Venice

Gross biochemical composition, energy value and condition index were investigated in two populations of Tapes philippinarum differently exploited by fishing in the Lagoon of Venice during the period July 2000-July 2001. Proteins, lipids, total carbohydrates and glycogen showed similar patterns in clams from all areas, highlighting the importance of the reproductive cycle and physiological features of the species in determining biochemical composition. The influence of environmental conditions and the effects of different fishing impact could also be observed. Carbohydrates exhibit minima in winter and maxima in spring-summer, while proteins have an irregular trend. Lipid seasonal variations are inversely related to glycogen contents; furthermore, lipids are higher in females than in males. Condition index and total energy content were influenced by both endogenous stress and environmental factors. In particular, the condition index, which gives an indication of the general physiological status of the animals, shows highest values in clams from the control area, not affected by fishing.