Why Do Fish Grow Forever? Rainer Froese Institute of Marine Science Kiel, Germany

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 A 95 = 3 / K 353 species with longevity and VBGF from FishBase

Longevity vs Taylor’s 3/K

Longevity vs Temperature

Longevity vs Maximum Length

Longevity vs Age at Maturity

Empirical Equations

Longevity vs Environment

Longevity vs Habitat

Nice Paper Submitted to CJFAS REJECTED Too narrow

Longevity vs Trophic Level

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 (L m / L max ) –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 (t m / t max ) –Fish 0.24 (n=229, LCL=0.224, UCL=0.253) –Marine mammals 0.13 ( LCL= , 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

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 m and about 0.8 tons weight. Killer whales (Orcinus orca) reach maturity in 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

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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