Fish age
Age determination
Method to estimate age
Theory
click to edit
Anatomical structure.
-Also known as hard part analysis
-Number of spacing and annual marks on a part of the animal that is retain throughout its life
Empirical methods
Recapture the populations at set intervals
Length frequency distribution-
-Lengths are taken from a large random sample of a population
-Number of individuals caught are plotted against length
-The resulting plot should reveal clusters indicating year classes, beginning with year zero.
Scale
Spiny-ray fishes.
Soft-rayed fishes
Otolith
Sagittal otolith bones (sagittae) –middle ear behind and to the sides of the brain
Also part of the balance and hearing systems for fish.
Regular/periodic annuli
Produce a series of periodic lines.
Used to estimate age and growth.
Random annuli
Produce disturbance lines
In general, denser or thicker layers of material are formed during periods of fast growth and less dense, thinner layers are formed during periods of slower growth.
Method to estimate age.
Tag-recapture studies; marking
Back-calculation
Marginal increment analysis
Radiometric/isotope analysis
Biological- parasitical, morphological, genetic marks.
Chemical- immersion, injecting, tattoing, feeding
Physical –internal and external tags