Age, Growth, and Mortality of Fish

Age and growth studies can be used to determine – maturity – age-related growth rates – survival/mortality rates, longevity – population age structure

Three Approaches to Aging 1. fish held in "confinement" or marked and released at known age and then recaptured primarily “validation” of aging process 2. length frequency assessment through modes in length-frequency distribution typically most valuable for one or two years does not work well in locations that lack well-defined growth seasons or are protracted spawners 3. anatomical approach most common based on calcified structure (hard parts) structures used depends upon species and latitude all are invasive except for scales

Length-frequency Distribution

Spawning biology

many fishes catfish, common carp suckers, sturgeon goosefishes, skates (marine) pikes yellow perch, smallmouth bass paddlefish scale => otolith => spine => fin rays => vertebrae => cleithrum => operculum => jawbone => Aging Fish by Hard Parts

Fish Scale Types

Features of a Ctenoid Scale focus annulus/annuli circulus/circuli ctenii radius/radii exposed portion buried portion edge

Scales may have well-defined annuli in northern U.S. because of defined seasons (at least first several years of life) Scales from fish living at more equatorial latitudes often lack annuli because of extended growing season False annuli can be formed when other stressors become involved, such as spawning, drought, etc.

Collection of Scales often with knife from particular areas on the fish take several because regenerated scales will be missing some annuli

Scale are read; if older and opaque, an impression is made by pressing between plastic or acetate slides Using a microfiche reader, such as in Miller Library

Annulus is actually the result of closely spaced circuli Age-2 White Crappie, collected in fall (just finishing third growing season)

Aging Fish by Scales 1st year growth 2nd year growth 3rd year growth

White Crappie collected in July; Age 5

Regenerated Scale

Otoliths lapillus, sagittus, and astericus - "ear bones" sagittal otolith commonly used for aging Semicircular canals of inner ear

Otolith removal

Used whole or sectioned by saw; sometimes polishing or burning the edge is required Age-6 White Crappie, spring Age-4 WHB, spring

Age-4 Yellow Perch, spring Opercula (singular: operculum)

Age-4 Smallmouth Bass, spring

Cross-section of a lake sturgeon fin ray showing annuli to estimate age (8yrs old).

Otolith and Scale of 5 Yr Brown Trout

What can be learned from aging studies: Comparison of Black Crappie (Pomoxis nigromaculatus) growth in 3 different lakes in South Dakota