VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

TECHNIQUES TO STUDY AGE AND GROWTH OF FISHES

AIM: To determine the age and growth of fishes

• The determination of fish age and growth is fundamental in fisheries biology and management. Such age-determined parameters as mortality and growth underlie the population dynamics models used in fishery analyses. Age studies can furnish other basic data such as stock, age structure, age at first maturity, spawning frequency, individual and stock responses to changes in the habitat, recruitment success, etc. Age and growth data also permit the determination of population changes due to fishing rates.

Age can be determined by one or more of the following methods:

• Anatomical method: Counting the regular growth marks formed in hard parts such as scales, otoliths, vertebrae, spines and tail bones.
• Length-frequency analysis: monitoring the progression through time of the identifiable modes in size classes.
• Direct estimate: through direct measurements of growth rate of specific specimens extrapolated to the stock as a whole. Marking and subsequent recapture of fish, or monitoring the growth of captive fish of known age are two direct estimation methods.