Effect of Pelvic Fin Ray Removal on Survival and Growth of Bull Trout

Abstract

Fin rays offer a viable alternative to scales and otoliths for determining ages of threatened salmonids, but information on potential side effects from their removal is limited. We conducted a laboratory study to assess the effects of removal of three pelvic fin rays on the survival and growth of two age-groups of bull trout Salvelinus confluentus (age 3: 209–298 mm standard length [SL]; age 4: 294–362 mm SL). Survival was similar between fin-ray-excised fish (≥73%) and control fish (≥69%) at each stage during the 169-d study (P > 0.85). Survival was also similar within age-3 (fin ray excision: ≥39%; control: ≥30%; P > 0.42) and age-4 bull trout (fin ray excision: ≥94%; control: ≥94%; P > 0.86), although a bacterial coldwater infection disproportionately caused higher mortality in age-3 fish for both test groups. Growth also did not differ between treatment and control groups of either age-3 or age-4 fish (P > 0.38). The fin excision wound was completely healed in 56% of treatment fish by day 33 and in 96% by day 126. Excised fin rays regenerated at the rate of 0.25% per day in 92% of treatment fish, attaining nearly one-half (42%) of the estimated total length by the end of the study; 90% regeneration was predicted to occur in about 13 months. Results suggest that removal of pelvic fin rays for aging is probably not deleterious to bull trout over the size range examined.