Caracteristicas poblacionales de Ampullaria scalaris d'Orbigny, 1835 (Mollusca, Gastropoda, Ampullariidae) en las Canteras de Los Talas (Berisso, Buenos Aires)
Population characteristics of A-scalaris Dorbingny, 1835 (Mollusca, Gastropoda, Ampullariidae) in the quarries of Los-Talas (Berisso, Buenos-Aires Province, Argentina).
MARTIN, S. M.
Natl. Univ. La Plata, Fac. Ciences Nat. & museo La Plata, Cic., Paseo Bosque,RA-1900 La Plata,Argentina
This work is focused in the analysis of biological parameters of the freshwater
snail Ampullaria scalaris d'Orbigny, 1835 from the quarries of Los Talas
(District of Berisso, Buenos Aires province, 34-degrees 53' South Latitude and
57-degrees 54' West Longitude). The collects were made during the period from
march of 1986 to january of 1988. These were made calculus of lineal regression,
coefficient of correlation; K factor of condition and an analysis of the modal
value of weights according to the sex.
By means of histograms were established the variations produced in this population at the level of length frequencies according to the sex and milimetric classes, monthly.
The conclusions arrived in this work, in agreement with the order of the treated subjects are the following ones. The relative growth between the total length of the shell and the total weight, has a high correlation for the two sexes. The factor K mean or condition, increases his value in all the individuals of greatest lengths, in males as in females. In the percentages of males and its proportion in relationship to the length, the proportion 1:1 was observed monthly in great part of the population. The frequency variation of the weight/sex function is of unimodal character and the mode is situated in the lesser weight class, which coincides with the lesser length individuals of this population. The length structure of this population and its anual evolution analysis, evidentiates that there exists one mayor group representated (30-35 mm). The juvenile class (5-15 mm) has an sustantial increase during the months of march to april, which indicates to us that these specimens are products of the massive ovipositions of november, december and january. The evolution of the length structure of A. scalaris demonstrates the life cycle is anual.
Studies on Neotropical Fauna and Environment, 28(4): 223-231. 1993.