Retention and Nonlethal External Detection of Calcein Marks in Rainbow Trout and Chinook Salmon

Abstract

An osmotic induction method was used to apply calcein marks to Chinook salmon Oncorhynchus tshawytscha and the Kamloops strain of rainbow trout O. mykiss (both migratory strains used for stocking into tributaries of Lake Superior). Preliminary exposure to a saline solution followed by immersion in a 0.5% calcein solution encouraged rapid infusion of calcein into fish tissues. Four-month-old Chinook salmon were exposed to a 1.5% or 5.0% salt solution to evaluate tolerance of different salinities and effects on mark intensity and retention. Rainbow trout were marked at three ages (2 weeks, 3.5 months, and 16 months posthatch) to evaluate the effects of age at treatment on mark intensity and long-term retention (a 5.0% preliminary salt bath was used). External detection of marks in scales, head, and fin rays was accomplished with a hand-held detector. The marking technique we used was well tolerated by both Chinook salmon and rainbow trout, and marks persisted into adulthood for rainbow trout treated at 3.5 months posthatch or later. The 5% salt concentration resulted in the persistence of more intense marks than did the 1.5% salt concentration. We demonstrated the potential applicability of calcein marks for instream population studies of migratory or anadromous species treated as fry or for studies involving release of post-fry-stage migratory or anadromous fish intended for recapture as adults.