Efficacy and practical limitations of calcein as a marking agent in Lake trout (Salvelinus namaycush) exposed to sunlight and frozen sample storage

Abstract

Marking and tagging fish is an important tool used in fisheries management. Calcein has shown potential as a marking agent for fish, but it is limited in field applications by sunlight degradation. In this study, three experiments were conducted to determine the long-term retention, effect of sunlight exposure, and the effect of freezing on calcein marks in unprocessed Lake trout Salvelinus namaycush samples. In experiment one the duration of calcein mark retention in Lake trout reared indoors was measured over a 1200-day period. Calcein marks were present throughout the 1200-day study in the head-jaw and caudal fins, however marks were not observed in otoliths or scales. Experiment two shows that sunlight had an adverse effect on mark retention over a period of 630 days. Fish reared in sunlight lost their markings in most tissues by day 150, but the parasphenoid and vertebrae retained markings throughout the study. Fish reared indoors in this study retained their calcein mark, although the percentage of fish with identifiable marks declined. In experiment three, the presence of calcein marks was evident throughout the experimental period, however freezing reduced mark intensity significantly in otoliths (P < 0.05) at day 30, 90, 180, and 270 post freezing compared to non-frozen Lake trout samples. No significant differences in reduced mark intensity (P> 0.05) by freezing occurred in the head-jaw, dorsal, caudal, or anal fins, and body scales, but variation increased across all tissues. No calcein marks could be observed in otolith and scale samples stored frozen for 36–72 months in experiment 1 and 2. This study found that sunlight exposure and extended frozen storage present limitations in calcein related research, however the parasphenoid and vertebrae were less affected by these two variables. These results provide useful information on the applicability and limitations of calcein in management settings and show that the parasphenoid is an excellent location for mark detection.