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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