Variações no comprimento dos indivíduos de uma população do mexilhão dourado, Limnoperna fortunei (Mollusca: Bivalvia: Mytilidae), ao longo do ano, na Praia do Veludo, Lago Guaíba, Rio Grande do Sul, Brasil

The individual size of Limnoperna fortunei (Dunker, 1857) was evaluated twice a month, for a year, based on samples from Veludo Beach (30o12'35"S, 51o11'68"W) in Guaiba Lake, southern Porto Alegre, Brazil. Physical and chemical data on water quality, such as temperature, transparency, depth, pH, dissolved oxygen, phosphorus, nitrogen, chlorophyll "a", and conductivity were also recorded. Adult samples were collected from underwater "sarandi" branches, Cephalanthus glabratus (Spreng) K. Schum (Rubiaceae), an aquatic macrophyte available at each site. Adults placed on artificial substrates were also checked every six months. Data were analyzed by applying multivariate statistics techniques related to the physical and chemical variables of the water and the density of individuals to estimate the patterns of the individual growth over the year. The adults were separated into three groups according to length classes: G1, G2 and G3 (groups 1 through 3). These three groups are related to the differences in behavior, namely, the ability of locomotion and fixation capacity. Individuals from Group 1 (5 to 7 mm in length) were the most abundant and were present in all the sampled months. Adults from artificial substrates were shown to display significant differences in seasonal growth and faster growth during spring and summer months.