P27Solustri

" CONTRIBUTION TO THE KNOWLEDGE OF SOME BIOLOGICAL
PARAMETERS OF Nassarius mutabilis (L.) IN THE MIDDLE ADRIATIC SEA "

Nassarius mutabilis (L.) is a gasteropod primarily carnivorous, feeding especially on dead animals, which lives on backdrops of thin and sandy-muddy bottoms, in depths ranging between 5 and 15 meters. This species, being very abundant particularly in the Middle Adriatic Sea, during the months from October to June is object of seasonal fishing from numerous small scale fishing agents. This period coincides with the reproduction of this species which occurs between the end of the winter and the spring. In spite of its great economic importance, N. mutabilis (L.) is a species still little known from the biological point of view, compared to other congeneric species, like for instance Nassarius reticulatus (L.). The present study is aimed to contribute to the knowledge of the biology and biometry of this neogastropod, through the analysis of the data obtained from around 2300 samples, with size (height of the shell) comprised in the range of 9-30 mm and originating from sampling which took place in two years, with the use of different instruments (dredge and traps) in the Middle Adriatic Sea. For each sample we have measured: the maximum height and the maximum diameter of the shell, the total fresh weight and the fresh weight of the meat. With these data we have therefore calculated the regression equations of the Height/Diameter_MAX, Height/Weight_TOT and Height/Weight_MEAT parameters. Besides, for the different seasons taken in examination, and for different depths, we have calculated the frequencies of length separately for males and female, classified through visual analysis of the sexual secondary characters. From the obtained results it has emerged that female have a greater average size than males, and that this difference is more marked in the winter and spring seasons, particularly for samples deeper than 10 meters, while during the summer season the size distributions are more homogeneous.