Portal de Periódicos da CAPES

Age and Shell Growth in the Freshwater Snail, Goniobasis proxima (Say)

1967; University of Notre Dame; Volume: 78; Issue: 1 Linguagem: Inglês

10.2307/2423381

1938-4238

Alan E. Stiven, Clarence R. Walton,

Fish Biology and Ecology Studies

To determine predictive relationships among size, growth, and age in the gastropod, Goniobasis proxima, field growth experiments were conducted in a small stream during the early fall of 1964. The relationship between growth per month (Y) and initial shell width (X) was given by log Y = 0.0422 0.1641 X. Using this equation and an estimated asymptotic shell width of 6.25 mm, an equation relating age and cumulative shell growth was ascertained to be of the form S 6.25 4.25 e-'0.1221 t where S equals shell width in mm and t is age in months. On the basis of a prior marking experiment and the size-age equation, maximum longevity under natural conditions was estimated to range from three to four years. A weight-size equation (log Y 6.937 + 0.412 X) was also developed where Y equals weight (live) in mg and X equals shell width. Consequently, with these last two equations it is possible to estimate both the age and weight of a snail from its shell width. INTRODUCTION The freshwater snail, Goniobasis proxima (Say) (Family Pleuroceridae), exists in relatively high and stable densities in shallow streams in the Piedmont of North Carolina (Foin and Stiven, 1966). Because of these high densities and subsequent ease of sampling, this species and its habitat provide an ecological system amenable to an investigation of the factors regulating population distribution and abundance. Little ecological work has been done on the pleurocerids, and virtually nothing is known of the population dynamics of Goniobasis proxima and the impact of the dense Goniobasis populations on the stream community. Goodrich carried out an extensive analysis of shell description, taxonomy, and geographic distribution of this group over a 40-year period and much of his bibliography is given by Rosewater (1959). Some ecological work has been done by Dazo (1962), principally on the natural history of G. livescens and Pleurocera acuta in Michigan. One of the most important prerequisites to population research is accurate fundamental life history knowledge, particularly aging criteria, which are mandatory in assessing age-specific mortality and a necessary first step in the construction of both actuarial and ecological life tables. This study, therefore, is concerned with the establishment of an aging criterion through the analysis of the size-age-growth relationship in a natural population of G. proxima. METHODS STUDY AREA Field growth experiments were conducted from 1 September to 1 November 1964 in Fern Spring, located on the southeastern lower