Why Do Fish Grow Forever?

Rainer FroeseInstitute of Marine Science

Kiel, Germanyrfroese@ifm.uni-kiel.de

Overview

• A look at longevity

• A look at growth

• Discussion

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

Taylor 1958

• Longevity as age at 95% of Linf

• A95 = 3 / K

• 353 species with longevity and VBGF from FishBase

Longevity vs Taylor’s 3/K

y = 0.8608x + 0.1983

R2 = 0.6525

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

-0.5 0.0 0.5 1.0 1.5 2.0 2.5

Taylor's maximum age (log; years)

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Longevity vs Temperature

y = -0.0142x + 1.3505

R2 = 0.0702

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1.0

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2.0

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0 5 10 15 20 25 30

Mean annual temperature (degree Celsius)

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Longevity vs Maximum Length

y = 0.6153x + 0.0252

R2 = 0.3714

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1.0

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2.0

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0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Maximum length (log; cm TL)

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Longevity vs Age at Maturity

y = x + 0.61

R2 = 0.674

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2.0

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Age at maturity (log; years)

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Empirical EquationsEquation

Nr

Intercept log

3 / K

log

Lmax

log

tm

T n R2 C.V.

1 0.1983 0.8608 353 0.653 0.2093

4 0.0252 0.6153 353 0.371 0.2814

5 0.6608 0.9277 229 0.680 0.1726

6 1.3505 -0.0142 353 0.070 0.3423

7 0.0096 0.7455 0.1754 353 0.671 0.2039

8 0.3930 0.4163 0.5593 229 0.752 0.1523

9 0.2731 0.8434 -0.0035 353 0.654 0.2084

10 0.3832 0.1893 0.7891 229 0.707 0.1655

11 0.2543 0.6371 -0.0166 353 0.466 0.2597

12 0.2611 0.3740 0.1085 0.5173 229 0.760 0.1501

13 0.0980 0.6849 0.2195 -0.0063 353 0.683 0.2005

14 0.2834 0.3411 0.1126 0.5158 281 0.748 0.1488

15 0.4136 0.4089 0.5513 313 0.744 0.1517

Longevity vs Environment

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Freshwater  Brackish  Marine

Environment

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Longevity vs Habitat

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Deep Demersal Pelagic Reef

Habitat

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Nice Paper

• Submitted to CJFAS

• REJECTED

• Too narrow

Longevity vs Trophic Level

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1.5 2.5 3.5 4.5

Trophic level

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Longevity vs Trophic Level

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Trophic level

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Longevity

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

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

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

Facts

• Relative size at maturity (Lm / Lmax)– Fish 0.44 (n=530, 95% LCL =0.421, UCL=0.451)

– Marine mammals 0.76 (n=9, LCL=0.716, UCL=0.803) – birds? reptiles?

• Relative age at maturity (tm / tmax)

– Fish 0.24 (n=229, LCL=0.224, UCL=0.253) – Marine mammals 0.13 (LCL= 0.0913, UCL = 0.198)

– Birds need 0.05 (LCL=0.0364, UCL=0.0695)

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.

Whale shark vs Fin whale

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0 10 20 30 40 50 60

Age (years)

Len

gth

(cm

)

Fin whale

Whale shark

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.

Great white shark vs Killer whale

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0 5 10 15 20 25 30 35 40

Age (years)

Len

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(cm

)Killer whale

Great white shark

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

Thank You