Calcein Mark Retention in Chinook Salmon and Steelhead Fry in Artificial and Natural Rearing Environments

摘要

Hatchery Chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss fry were marked with calcein dye to determine its efficacy for identifying fish after release into the stream environment. The effects of the dye treatment on growth and survival of marked fish and the retention of the marks over time were evaluated in the presence and absence of sunlight. Minimal differences in growth were observed between marked and unmarked Chinook salmon, and there was no difference in the total length of marked and unmarked steelhead at the conclusion of the study. Calcein marking had no effect on survival of Chinook salmon or steelhead fry during the 8-week experiment. The calcein mark rapidly lost its intensity over time in Chinook salmon and steelhead. Steelhead fry were marked and reared in three light treatments to directly evaluate whether sunlight exposure affected calcein retention. After 28 d, steelhead exposed to sunlight had no visible calcein marks, whereas those held in covered tanks had 100% mark retention. Chinook salmon fry were monitored in stream habitats after release into the stream environment. No marks were visible 8 months after release. These observations demonstrate reduced calcein mark retention in fish exposed to natural sunlight. Calcein mark retention differed between Chinook salmon and steelhead. Because externally visible calcein marks have a finite life span in the presence of sunlight, calcein use in long-term fish-marking projects will be limited.