Fish Age + Growth + Causes of Death

how to age fish

shark vertebrae (count)

bones

scales (not accurate, only good for young fish)

otoliths

basically any bony part

counting via otolith

count the rings

lay down ring every year of life dependent on feeding (grow diff during diff szns), harder for tropical fish b/c less seasonality

width between rings can tell you about the year OR about fish that migrate (also chemical signatures of where they were)

von Bertalanffy indeterminate growth equation

L(t) = L(8) (1-e^-k(t-to))

L = length

L (8) = asymptotic or max L

t = time

e = natural log

k = rate constant

von Bertalanffy growth model

length vs age

fewer large fish b/c they’re all being caught by recreational + commercial fishes, growth rate slows @ maturity, every fish has a unique growth curve + life expectancy (short-lived fish grow more slowly?)

allometric growth

y = weight

a = constant

x = length

b = slope

length vs weight

much less variation, very accurate estimate at weight if measure the length

causes of death

natural mortality (m), accident (episodic events), fishing

natural mortality (m)

predation, accident, starvation, opportunistic pathogens/disease, senescence

senescence

semelparous species

die after reproducing, overproduction of steroids + cortisol

accident

episodic events

pathogens

not common in sharks or natural environment, common in aquarium fish (marine ex: blacksmith)

hyperadrenocorticism

degenerating internal organs