Age, Growth, and Mortality of Fish. Age and growth studies can be used to determine – maturity –...

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

many fishesmany fishescatfish, common carpsuckers, sturgeongoosefishes, skates (marine)pikesyellow perch, smallmouth basspaddlefish

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