Otolith
A recognizable mark is created in the otoliths through subjecting fish to a change in temperature or chemicals. Chemical otolith marking is mostly done by submersion in a chemical solution (strontium chloride, tetracycline, calcein) or through the food provided to fish. Distinct and recognizable patterns appear in the otolith structures by exposing fish to different temperature regimes.
Advantages:
- A large number of fish of any size may be marked within a short time
- The mark is permanent and has little impact on fish health
Disadvantages:
- Detection requires sacrificing fish or recovering carcass for the extraction of an otolith
- Analysis of otoliths is expensive, time consuming, and requires special equipment
- Thermal marking requires precise control of temperature and knowledge of growth patterns at different temperatures