Confirmation of daily increment deposition in otoliths of young razorback suckers

Increments were deposited in otoliths of laboratory-reared razorback suckers (Xy- rauchen texanus) just after hatching in either fluctuating (16 degreesC +/- 2.5 degreesC) or constant (16 degreesC) temperature treatments. Otolith increment counts of fish reared in fluctuating temperature were similar to the post hatch age of fish up to 49 days old and should be a reliable predictor of age. Otolith increment counts of fish reared in constant temperature underestimated age of fish up to 49 days old by 4 to 7 days. Total length of fish and otolith size (lapillus diameter) were similar among fish reared in constant or fluctuating treatments. Minimal variation of otolith increment counts and age estimates between readers suggests multiple counts may be unnecessary Validation of patterns of regular increment deposition in otoliths of wild-caught razorback sucker larvae and early juveniles allows estimation of hatching dates and subsequent growth rates. Such information could be used to manage river flows and floodplain habitat critical to the survival and recovery of this endangered species.