Fish Conservation and Management

CONS 486

Fish metabolismReading - Diana Ch. 3

Fish metabolism topics• Metabolism

– Aerobic vs anaerobic

– Standard vs active

• Role of temperature

– Temperature preferences

• Scope for activity

– Optimal temperature

– Decline in scope and scope reaching zero

• MAJOR THEME ALERT! Linking science and management

Major theme: Linking science to conservation & management

• Harvest regulations

• Managing fisheries & habitats

• Protecting populations & habitats

• Restoring populations & habitats

• Fisheries exploitation data

• Applied life history data

• Human dimensions: socio-economic data

• Physiology

• Behaviour

• Population ecology

• Ecosystem ecology

• Habitat data (limnology, oceanography)

• Life historyBasic science

Applied science

ManagementConservation

Conservation Physiology• Is an emerging scientific discipline

• Conservation focuses on understanding biology that relates to natural resource use, protection, sustainability

• Physiology focuses on understanding the mechanisms of how organisms work

• Defined as “An integrative scientific discipline applying physiological concepts, tools, and knowledge to characterize biological diversity and understand responses to environmental stressors”

• We’ll work through some examples today!

Recommended read!

http://faculty.forestry.ubc.ca/hinch/Cooke_etal_2012_PhilTransRoyalSocB.pdf

Metabolism introduction• Energy: the ability to do work!

• Metabolism: chemical reactions that convert stored energy into usable energy

• Energetics: the study of the processes involved in energy conversion

publicdomainpictures.net

Metabolism introduction• For fish, metabolism can be energetically costly!

– Highly variable between species & age classes

– Strong role of environmental conditions especially temperature

• Metabolism can cost between 8 and 100% of ingested energy

– Often even this is not enough and additional body energy reserves are required

• Goal of today: to overview this process and examine the factors that contribute to this variation

A Tale of Two Types of Metabolism

Aerobic, and its evil twin, anaerobic

Aerobic metabolism• Aerobic metabolism: conversion of glucose (from stored

energy in the body) in the presence of oxygen into carbon dioxide, water and energy

C6H12O6 + 6O2 >> 6CO2 + 6H2O+ ATP + heat

• Adenosine triphosphate (ATP) temporarily stores energy

– ATP circulated to tissues or organs for immediate use or stored

• This reaction is not 100% efficient and heat is also produced as waste

When do fish use aerobic metabolism?• Primarily used during routine feeding and swimming

activities

• For fish, “red” muscle is involved in aerobic metabolism

– tiny amount of muscle compared to body mass!

• This reaction can continue indefinitely as long as oxygen and glucose are present

Red muscle

White muscle

View of one side of a yellowfin in cross-section

Shadwick R E , and Syme D A J Exp Biol 2008;211:1603-

1611

©2008 by The Company of Biologists Ltd

Anaerobic metabolism• Takes place when fish need energy but blood O2 is limited

• Glucose is still converted to ATP, but oxygen is not needed!

• BUT this is much less efficient than aerobic metabolism

– 13X less energy produced

– Produces a byproduct known as lactic acid

– Lactic acid accumulation can have long-term effects including swimming impairment and mortality

– Oxygen is required to eliminate lactic acid

Cooke et al. Proc Royal Soc B 2012

- critical level- could result in death

Take-home points

- Different types of fishing gear cause different levels of anaerobic activity

- Some gears may cause fish to be so hyperactive that they may not be able to recover if released

When do fish use anaerobic metabolism?

• For fish, “white” muscle is involved in anaerobic metabolism

• But only used in occasional situations

– Burst swimming, e.g., predator avoidance

or migration through hydraulic barriers

– Feeding

Why have fishes evolved musculature containing so much white muscle??

CON - It is energetically costly to maintain.PRO – ‘insurance policy’

Standard vs active

• Two extremes when describing aerobic metabolic rates for fish are:

• Standard metabolism: the rate of energy use by fasting fish at rest

• Active metabolism: the rate of energy use that a fish can sustain as a result of swimming activity

– Standard is a component of this

Swim tunnels used to measure metabolic and cardiac performance

• Metabolic rates are related to swimming activity in an exponential fashion

– If you log transform this, it becomes linear

(Figure 3.3 Diana)

• Anaerobic (burst) swimming is costly!

• E.g., consumption of 10mg O2 by juvenile sockeye (50 g, 16 cm)

– No swimming (standard met.): 3 h

– Max sustained (active met.): 15 min

– Max burst (max anaerobic met.): 20 sec.

(Figure 3.9 Diana)

160

128

80

32

cm/s

• Standard metabolic rate increases with weight

• But when considering it as ‘per unit of weight’, it declines

(Figure 3.10 Diana)

Temperature affects metabolic rate!

• Ectotherms: body temperature is controlled by external temperatures, as opposed to an endotherm)

• Poikilotherms (or heterotherms): body temperature varies, as opposed to a homeotherm

• Most fish have body temperatures that are same as water temperatures

• A few fish species (e.g. sharks and tunas) can generate heat and store it (endothermic poikilotherms)

(Figure 3.8 Diana)

• Relationship between metabolic rates and temperature (10 g sockeye, 150 g bass)

• Standard metabolism increases in an exponential fashion with temperature

• Active metabolic rate also increases (but not necessarily exponentially) to a max value at intermediate temperatures, then declines

• The difference between the active rate and the standard rate is known as the scope for activity (Fry 1947)

Scope for Activity

Temperature (C)

standard metabolism

activemetabolism

Where is scope greatest?-15 C sockeye, 30 C bass-we call these temperatures the ‘optimum’ or Topt

Why does scope decline above certain temperatures?

• ↑ temp becomes stressful to fish and it can reduce scope

• The ability of water to hold O2 is reduced at high temperatures

– Yet standard metabolic rate is increasing therefore fish must ventilate to increase O2 uptake

• Stress metabolites and enzymatic dysfunction at warm temperatures:

– Can diminish heart function

– Limit amount of oxygenated blood that can circulate, reducing scope

• Total metabolic demand of fish can actually exceed the aerobic scope for activity

• Supplementary energy provided anaerobically (but recall that this is inefficient and produces toxic byproducts!)

Why did those curves differ between species?

• Need to consider ‘thermal guilds’

– Sockeye are coldwater fish with a narrow temperature ranges (stenotherm)

– Bass are warmwater fish with broader temperature ranges (eurytherm)

• Evolutionary trade-off between scope and survival

– Sockeye adapted to grow best at only cool temps but have high scope whereas bass can survive across a broader range of temps but have lower scope

Farrell et al. 2009 CJZ

Area under the curve represents ‘aerobic scope’

Optimum and Critical temperatures• Temperature where scope is greates enables fish to aerobically swim

their fastest for prolonged periods of time (Topt)

– Often fish survive and grow best at these temperatures because it is most efficient for pursuing prey and escaping predators!

• Fish would die if metabolic rates were continually out of the scope range (approaching or at ‘critical temperatures’ - Tcrit)

Standard metabolism

Activemetabolism

Temperature

Eliason et al. 2011 Science

Scope and migration temperature for several sockeye populations in Fraser watershed

-Smoothed curves are estimated aerobic scopes-Histograms are temperature frequencies encountered during up-river migration

Take home point – Topt from lab experiments coincides with most frequently encountered river temperaturesWhat are the implications?

Note how Topt and Tcrit varies among populationsNote that Weaver has lowest Topt and Tcrit

Ae

rob

ic s

cop

e a

tT o

pt

Sockeye populations with harder migrations have higher scopes

Linking science and management

• How can we use ‘Scope’ in management?

• A sustained high temperature event occurred in the Fraser River in 2004

– DFO reported mass mortality for migrating sockeye salmon particularly in Weaver stock (> 80% mortality)

– Weaver sockeye have one of the lowest Tcrit (~20 C)

– Weaver sockeye encountered several days > 20 C

• Aerobic scope could help to forecast potential migratory mortality arising from high temperatures – Used to reduce level of fishery to ensure adequate numbers of fish are allowed to

reach spawning grounds assuming large numbers may die enroute if Tcrit is expected to be surpassed