Abstract
To better understand the reliability of fin clipping as an external mark for early-summer (<100 mm TL) age-0 Northern PikeEsox lucius, we experimentally evaluated fin regeneration following complete excision of a pelvic fin over 98 d. The Northern Pike were also marked with a unique visible implant elastomer tag to allow for repeated measures of individuals. Survival, growth, and fin regeneration were evaluated among three treatment groups to determine whether the fish that received a fin clip following anesthetic (n = 17) differed from those that were fin-clipped without anesthetic (n = 17) and unclipped control fish (n = 10). The fish were distributed proportionally by treatment group between two outdoor rearing tanks, but one of the rearing tanks experienced a mortality event from an unknown source. Consequently, the evaluations were based on the 25 surviving Northern Pike, with treatment-specific sample sizes of seven fish for both the control and nonanesthetic treatments and 11 fish from the anesthetized treatment group. Despite the mortality event in one of the two rearing tanks, survival was similar among the three treatment groups when the rearing tanks were evaluated independently and pooled rearing-tank data revealed no difference in growth rates between fin-clipped and unclipped control fish for TL and weight. By day 46, the clipped fin had regenerated to approximately 80% the length of the unclipped counterpart and by the end of the study many of the clipped fins were nearly indistinguishable from the unclipped fins. This represents the fastest age-0 esocid fin regeneration reported. The results from this study demonstrate that marking early-summer age-0 Northern Pike during the growing season with pelvic fin clips is likely inappropriate for mark-recapture studies that span beyond 3 months. The use of fin clips on age-0 Northern Pike should be restricted to shorter-term studies, or an alternative marking technique should be adopted for the reliable identification of the fish.