Fish Marking

1. Fish Marking Not in your textbook!

2. Reasons for marking fishes • To identify stocks • To assess stock size • To assess growth and mortality rates Mark must have minimum interference with biology of fish while having maximum utility

3. Requirements of the mark • 1) persist for life of fish • 2) not interfere with behavior • 3) not make fish more vulnerable to predators • 4) not tangle with weeds or nets • 5) easy to apply (minimize equipment, stress to fish) • 6) applicable to broad range of sizes

4. More requirements • 7) variable to allow distinctive marking of groups • 8) not create health hazard • 9) easily detected in field by untrained people • 10) inexpensive, easy to obtain • 11) minimum confusion in reporting • 12) remain unaffected by preservatives • 13) no effect on growth or survival of fish

5. Selection considerations • 1) length of time • 2) skill of personnel • uniform application, minimum disturbance • 3) species to be tagged • 4) means of recovery • commercial or sport fishery (incentive) • 5) concurrent marking programs

6. Types of marks • 1) tags • 2) fin clipping • 3) branding • 4) dye • 5) tattooing • 6) subcutaneous injection • 7) genetic

13. Determining the Age of Fish

14. Useful fish structures In temperate regions, fish growth is seasonal. Changes in growth rate are recorded in the growth of hard structures in fishes. These structures can be used to determine fish age.

15. Scales

16. Otoliths

17. Fin rays/spines

18. Cleithra

19. Vertebrae

20. Various useful structures

21. Various useful structures

22. Back calculation Growth of fish scale is proportional to growth of fish length Length at each age can be determined from scale, if fish length is known