Validation of daily growth increments in otoliths to age threespine stickleback ( Gasterosteus aculeatus )

Hypothesis: Threespine stickleback deposit daily growth increments in their otoliths. Organism: Anadromous threespine stickleback (Gasterosteus aculeatus) from Rabbit Slough, Alaska. Methods: We reared stickleback from an in vitro cross for 95 days in a large outdoor pool and analysed the sagittae of specimens from weekly samples. Results: Putative daily growth increments in otoliths were significantly correlated with true age in days (r = 0.97). Other relationships, such as those between age and otolith radius (r = 0.72), and between standard length and number of increments (r = 0.63) or otolith radius (r = 0.51), were also significant though not as strong. Conclusions: These data are consistent with published results for resident freshwater threespine stickleback from Great Britain, a different clade, continent, latitude, ecological system, and fish life history. Ageing young-of-the-year threespine stickleback with daily growth increments in their otoliths thus appears to be possible for distantly related populations with different life histories and locations. Daily growth increments in the otoliths of young stickleback provide a powerful tool for investigating life-history evolution or any subject that employs precise age as a covariate, since age of wild-caught fish can be associated with a suite of fitness measures, phenotypes, or genotypes.