Age and Growth of Chamelea Gallina From the Algarve Coast (Southern Portugal): Influence of Seawater Temperature and Gametogenic Cycle on Growth Rate

The age and growth of Chamelea gallina from the Algarve coast (southern Portugal) were estimated using three methods: (1) counting of external shell rings; (2) examination of shell microstructure (acetate peels); and (3) length–frequency distribution analysis. The Von Bertalanffy growth curves obtained by these methods were, respectively: Lt = 37.55[1 − e−0.71(t + 0.01)]; Lt = 38.95[1 − e−0.47(t + 0.24)]; Lt = 42.15[1 − e−0.32(t + 0.76)]. Based on these results, and taking consideration of the biology of C. gallina along the Portuguese coast, counting of external rings is appropriate for a quick estimate of age, while the use of acetate peels is recommended for the estimation of Von Bertalanffy growth parameters. The analysis of acetate peels showed that periods of major growth occurred between December and July. Slower growth periods were registered at the beginning of autumn, especially in October, when all individuals of the population showed narrow growth increments associated with a cleft in the shell ventral margin. This slowing of the growth rate appears to be related to a decrease in seawater temperature. The gametogenic cycle may also influence growth rate, which decreased after spawning (September to November) and increased with the onset of gametogenesis (November).