Why Do Fish Grow Forever?

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Why Do Fish Grow Forever?

• Rainer Froese
• Institute of Marine Science
• Kiel, Germany
• rfroese_at_ifm.uni-kiel.de

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Overview

• A look at longevity
• A look at growth
• Discussion

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Longevity in Fish

• Maximum age on record for a species
• Used for
• r versus K strategists
• proxy for natural mortality
• 1 of 5 criteria to estimate resilience

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Taylor 1958

• Longevity as age at 95 of Linf
• A95 3 / K
• 353 species with longevity and VBGF from FishBase

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Longevity vs Taylors 3/K
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Longevity vs Temperature
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Longevity vs Maximum Length
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Longevity vs Age at Maturity
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Empirical Equations
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Longevity vs Environment
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Longevity vs Habitat
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Nice Paper

• Submitted to CJFAS
• REJECTED
• Too narrow

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Longevity vs Trophic Level
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Longevity vs Trophic Level
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Why Do Fish Grow Forever?

• Textbooks
• Lagler et al. (1977)
• "...birds and mammals have to expand part of
  their caloric intake for the maintenance of body
  temperature and in supporting themselves fish in
  contrast are poikilotherms and get such support
  from the surrounding water."
• Fishes living in a fluid medium that supports
  them mechanically can continue growth throughout
  their lives...
• Fish are far superior in protein-building than
  domestic live-stock

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Alternative Hypothesis Assumptions

• Access to food is not different among the
  considered groups
• Adult size has evolved to best fit the respective
  niche
• Animals strive to reach adult size as fast as
  possible

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Alternative Hypothesis

• Fish growth is limited by the need to extract
  oxygen from water
• Fish grow as fast as they can, but it takes them
  forever to reach maximum size
• Size at maturity is less then maximum size
  because they can not afford to wait forever
• Fish need longer than air-breathers to reach size
  at maturity

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Facts

• Relative size at maturity (Lm / Lmax)
• Fish 0.44 (n530, 95 LCL 0.421, UCL0.451)
• Marine mammals 0.76 (n9, LCL0.716, UCL0.803)
• birds? reptiles?
• Relative age at maturity (tm / tmax)
• Fish 0.24 (n229, LCL0.224, UCL0.253)
• Marine mammals 0.13 (LCL 0.0913, UCL 0.198)
• Birds need 0.05 (LCL0.0364, UCL0.0695)

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Whale shark vs Fin whale

• The largest fish, the Whale shark (Rhincodon
  typus) needs about 9 years to reach maturity at
  about 5.5 m and 750 kg, and about 60 years to
  reach a maximum length of 14 m and 12 tons.
• The fin whale (Balaenoptera physalus) needs about
  7 years to reach maturity at a size of about 20 m
  and about 36 tons, with a maximum size of about
  25 m and 70 tons.

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Whale shark vs Fin whale
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White shark vs Killer whale

• The Great white shark needs 36 years to reach a
  maximum size of 7.2 m and 3.4 tons females take
  about 12 years to reach maturity at 4.5-5 m and
  about 0.8 tons weight.
• Killer whales (Orcinus orca) reach maturity in
  6-10 years at 5-6 m length and about 1.8 tons
  weight, with the typical size of about 7 m and
  3.8 tons reached a few years later.

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Great white shark vs Killer whale
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Conclusion

• Fish clearly lack behind the growth performance
  shown by marine mammals and birds.
• Their relative size at first maturity is
  significantly lower than in birds and mammals,
  yet they take relatively longer to reach that
  size.
• Gills suck

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Thank You