Length-Weight Relationship and Distribution of Tympanotonus Fuscata (Mollusca: Potamididae) in Brenu Lagoon, Ghana

Abstract

A total of 1894 specimens of Tympanotonus fuscata were obtained by random sampling with Ekman grab from Brenu Lagoon to determine the size distribution of the organism as a result of perceived human predation on the resource in the area. Samples of the edible snail were col-lected monthly from November 2003 to October 2004, and the physico-chemical parameters de-termined for the entire study period. Variations were observed in the quarterly mean density (numbers/cm3) of the snails in all the four sampling stations A to D with values ranging from 18.67±4.81 to 99.00±17.80 at station A, 21.67±7.06 to 29.33±4.41 at station B, 21.70±10.50 to 71.70±12.30 at station C and 9.67±7.22 to 41.30±5.70/ cm3 at station D. There were patchy distri-butions of the snail in the lagoon at replicate stations which might be due to the variation of physical conditions in the water. The height-weight relationship of the snail indicates negative allometric growth with high individual variability and the body weight was most closely related to the shell height (R² = 0.89). The snails in Brenu Lagoon were not growing to the large size this was observed in size frequency distribution. The modal size class was 1.5 – 1.9 cm. The domination of smaller snail size could be due to human predation pressure on the larger snails and or the effect of physical and chemical factors that prevail in Brenu Lagoon.