Factors affecting the production of daily growth increments in the otoliths of fishes
Creators: name: Campana, Steven E.
Publisher: name: University of British Columbia
Year: 2010

description: Otolith growth in young fishes occurs with a circadian periodicity, resulting in a concentric growth record of calcareous material. The resultant sequence of daily growth increments is often punctuated by prominent checks (discontinuities). Yet little is known of those variables that may control or modify the production of one increment per day and/or checks. The objective of this thesis was threefold: 1) to assess the influence of some environmental variables on daily increment production 2) to develop a mechanism and explanation for check formation 3) to interpret the otolith microstructure of wild fishes in terms of knowledge gained from the first two objectives. The influence of light and temperature on daily increment formation was the subject of the first experiment. Tetracycline injected into juvenile starry flounders (Platichthys stellatus) was incorporated into the periphery of the sagittal otoliths within 24 h. The resulting band, visible under ultraviolet light, was used as a dated mark on the otolith growth increments. This technique was used to verify that increments were laid down on a daily basis, both in field and laboratory environments. Sub-daily increments were visible in otoliths of fishes reared under most environmental conditions. The production of daily increments in juvenile starry flounders preconditioned to a natural environmental regime was unaffected by photoperiod or temperature fluctuation, suggesting the presence of an internal circadian rhythm. Juvenile steelhead trout (Salmo gairdneri) and starry flounders were reared 64-76 d under various experimental feeding regimes to determine if feeding periodicity influenced the production of daily growth increments on the otoliths. Both species produced daily increments when fed thrice daily, daily or once every three days, as well as through 26-32 d of starvation. Daily growth increments were also deposited in vateritic ("crystalline") otoliths, which comprised 27% of the trout sagittae sampled. Feeding frequency affected increment appearance and the incidence of subdaily increments in trout, but not in flounders. The difference in effect was probably due to the higher metabolic rate of trout. Increment deposition in all flounders was far more variable than in trout, and some flounders apparently ceased increment formation altogether. Since the results of the first two experiments were apparently contrary to some previous studies, I suspected that age may interact with light and/or temperature to influence otolith growth. Plainfin midshipman, Porichthys notatus, were reared in the laboratory under three environmental regimes to determine the influence of certain variables upon otolith growth increment formation. Both larval and juvenile midshipman were used to test diel cycles and constant conditions of light and temperature. In the absence of a diel photoperiod, daily growth increments were not formed upon hatch. However, after an acclimation period of 2-3 wk, an endogenous circadian rhythm became evident, resulting in daily increment production. With increasing age, the influence of light as a zeitgeber decreased, while daily increments became more prominent in all environments. Temperature fluctuation affected increment appearance, but did not entrain increment deposition. Periods of stress can disrupt daily growth increment formation on a fish otolith, producing a check (discontinuity). Calcium-45 was used to monitor calcium deposition on the sagittae of coho salmon, Oncorhynchus kisutch, during periods of check formation. "5Ca deposition on the otolith continued for 12 hr after transfer from a5Ca water. When stress was applied during fl5Ca immersion, tt5Ca deposition was reduced. However, stress applied immediately after transfer from a5Ca water had no effect on U5Ca deposition. Stress indirectly disrupted *5Ca deposition on the otolith through a reduction in branchial uptake of calcium. Check formation was not associated with resorption of otolith calcium. "Lunar" growth patterns have been observed in the otoliths of many marine fishes. I examined the otolith microstructure of juvenile starry flounders sampled from a monitored environment for evidence of lunar periodicity. Three types of biweekly cycles were observed in all of the flounder otoliths; two of the cycles were correlated with a tidal modulation of the environment. Through a multiple regression model, much of the day-to-day variability in daily increment width could be explained by daily variations in temperature, salinity and tidal mixing. My results suggest that a 15-d increment width cycle was entrained by the interaction of a 15-d tidal cycle with temperature and salinity. The same tidal cycle/temperature interaction probably produced a semi-lunar pattern of increment contrast. However, the presence of otolith checks formed at weekly and/or biweekly intervals could not be so explained, although checks were consistently formed on the new and full moons.