Length-Weight Relationships and Monthly Variations in Body Weights and Condition Indices of Two Clam's Species; Venerupis aurea and Tapes decussata in Lake Timsah, Egypt

Document Type : Original Article

Author

Zoology Department, Faculty of Science, Fayoum University, 63514 Fayoum, Egypt

Abstract

Both Venerupis aurea and Tapes decussata are commercially exploited bivalves, and their populations
have been severely declining in Lake Timash (Suez Canal, Egypt). Weight-length relationships and
monthly changes in body weights and condition in relation to water temperature and gonadal cycle
were studied for the two bivalves in this lake. All regressions between body weight and shell length
showed higher determination coefficients (R2). Total weight and shell weight of the two clams
increased isometrically with length in most months. Both flesh weight and dry flesh weight indicated
negative allometric and isometric relationships to length in most monthly samples of V. aurea and T.
decussata, respectively. Body condition was evaluated through three condition indices (CI). Results
showed that digestive gland weight of the two species is a good index for body condition. Variations in
body weights and the condition indices showed no clear seasonal pattern. Changes in gonad weight and
condition indices did not appear to be related to temperature fluctuation. However, temperature
correlated negatively with flesh weight of V. aurea (R=-0.617, P<0.05) and T. decussata (R=-0.826
P<0.0005). Although a non-significant correlation was observed between gonad weight and body
condition, a clear decline of CI1 and CI2 was found during spawning periods of the two clams. The
highest CI3 value of 3.63 in August 2004 for V. aurea and of 3.45 in November 2004 for T. decussata
occurred as a prelude to major spawning.

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