Growth rate variability and lipofuscin accumulation rates in the blue crab Callinectes sapidus

Abstract

To better understand growth and age-pigment (lipofuscin) accumulation rates of the blue crab Callinectes sapidus under natural conditions, juveniles (33 to 94 mm carapace width) were reared in outdoor ponds for over 1 yr. Growth rates, measured by carapace width, during summer and fall exceeded all those reported in the literature; the initial carapace width of 59 ± 14 mm (mean ± SD) increased to 164 ± 15 mm within a 3 mo period. No growth occurred during winter months (Novem- ber to April) at low water temperatures. Growth rates of crabs in ponds were substantially higher (von Bertalanffy growth parameter K = 1.09) than those of crabs held in laboratory environments, and than rate estimates for natural populations of mid-Atlantic blue crabs. Model comparisons indicated that seasonalized von Bertalanffy growth models (r 2 > 0.9) provide a better fit than the non-seasonalized model (r 2 = 0.74) for pond-reared crabs and, by implication, are more appropriate for field popula- tions. Despite growth rates that varied strongly with season, lipofuscin (normalized to protein con- centration) accumulation rate was nearly constant throughout the year. Although the lipofuscin level in pond-reared crabs was significantly correlated with size (carapace width), it was more closely cor- related with chronological age. Lipofuscin accumulation rates were also similar to those observed for laboratory-reared crabs, despite very large differences in growth rates and temperature regimes. The constancy of normalized-lipofuscin accumulation rates of blue crabs across seasons and environmen- tal conditions suggests that lipofuscin concentration can be a more robust indicator of age than cara- pace width alone.