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Bioenergetics
budgeting the fires of lifeK. Limburg lecture notes
Fisheries Science
Reading
: Adams, S.M., and J.E. Breck. 1990. Bioenergetics.
In C.B. Schreck and P.B. Moyle, editors. Methods for FishBiology. AFS Books, Bethesda, MD.
Giovanni di Paolo (
th^ cent.),
for Dante’s Divine Comedy
What is bioenergetics?
The study of the processing of energyby living systems,
at any level of
biological organization.
In fisheries science, we typically
- consider the bioenergetics of individuals• use this to develop budgets for populations• make projections about fish production in particularareas (e.g., Lake Ontario salmon production) Fish bioenergetics is a subset of a much broader fieldcalled
ecological energetics
Lake B
Lake A
June 1
June 1
Sept 1
Sept 1
Why would growth be different?
Review: the first two Laws of Thermodynamics1. Energy and matter cannot be created
or destroyed, but they can be changedfrom one form to the other
Any transformation of energy or matterresults in some loss of “useful” energy –in other words, no energetic process is100% efficient
(entropy, the tendency toward disorder, is like an‘energy tax’)
Source: Dodson, 1998
10
Hypothetical energy flow through a food chain
Energy budgets:
- are like bank accounts: inputs (like deposits),outputs (like withdrawals), storage (like yourbank balance), and growth (like interest)- has to balance!
Inputs = Outputs + Growth
- should always use the same units (likecurrency)- examples of typical units: calories or joules[energy], carbon, or even biomass (grams)
Energy budget for a fish:
Consumptionor ration (C)
metabolic costs (M)
excretion
(U)
fecal egestion (F)
What is left over?
Writing the simplest form of the energy budget:
C = M + G + U + F
Energy
food
= Energy
metab.
growth
Energy
excreted
egestion
assimilated
unassimilated
Growth (G) is often separated (for adults) intosomatic and reproductive components:
G = G
S
R
Gives you your S
t
Gives you S
t-
t
time t-
t^
time t
time t+
t
S
t
Next time interval: S
t-
t
=
A very commonly used model is one developed byMalcolm Elliott and Lennart Persson (and described inyour reading, p. 397-399)
t k
t k
t
t
t^
e
t k e S S C
1
)
(
C
t^
= consumption rate, mg
food
/g
fish
, within period t
S
t^
= weight of stomach contents, mg
food
/g
fish
, in period t
k = the
gut evacuation rate, time
t = the time interval between measurements
The parameter
k
(gut evacuation rate) can be
estimated experimentally, or else by using datafrom a time in the field measurements when fishare not feeding (and so food is only passingthrough the guts).
k = (1/
t) ln(S
t’
/S
t”
)
where t’ and t” mark the beginning and end of anon-feeding time period.
3530252015105 0 6:00 AM Try the example in Box 12.1 (p. 399) in the reading!
12:00 PM
6:00 PM
12:00 AM
6:00 AM
mg/g
Gut contentsC_t
Elliott and Persson’s model works best when:1. Fish feed continuously during daylight2. Amount of food varies during sampling period3. Exponential digestion rate/evacuation rate (k)4. Fish consume large number of small prey items
The Various Components of
Metabolism
Standard metabolism•^
closest approximation of basal rate
-^
fish should be quiet, unstressed, notswimming, not feeding or digesting
Routine metabolism•^
routine activity of a non-feeding fish
-^
typically measured in an aquarium or othercontrolled space
C =
M
+ G + U + F
Metabolism, continued.
Active metabolism•^
additional metabolic cost of activity(swimming)
-^
will be a function of swimming speed
-^
also whether metabolism is aerobic oranaerobic:
1 mole of glucose (C
H 6
12
O
) = 686 kilocalories (kcal) 6
Aerobic respiration: consumes the glucose, produces36 moles of ATP, equivalent to 262.8 kcalAnaerobic: produces only 3 moles, equiv to 21.9 kcal
Metabolism, continued.4.^
“Feeding metabolism”•^
energy used to digest food
-^
called “heat increment” or “specificdynamic action” in Animal Science (SDA– term used by lots of fisheriesbiologists)
Source: Diana 1995
Can vary quite abit, depending onitems in the diet
Metabolism is affected by two major factors:BODY SIZE (weight) and TEMPERATUREWeight effect:The bigger the fish, the lower its specificrespiration rate (that is, R/g)
R
W
k
“is proportional to”
“k” variesbetween 0.4 to0.8,determinedexperimentally(allometricrelationship)
Temperature effect:
Most fishes are both ectothermic (body Tcontrolled externally) and poikilothermic(body T varies)Q: what are the antonyms to those terms?Exceptions: tunas and some sharksGeneral relationship of standard metabolicrate (M
) to temperature (T) iss^
M
s^
= a e
mT
(T is taken to be the ambient watertemperature)
M
s^
= a e
mT
Taking the natural log transform of this gets you
ln(M
) = ln(a) + mTs^
Temperature is a very powerful controller of growth.Most fish have an optimal temperature for growth.
Finally, a fish’s metabolic rate is also affected by itsactivity, and this is also described by an exponentialfunction of the form
e
gS
where S = swimming speed and g is an experimentallydetermined constant.
We can put all of this together in a single equation:
M
standard + active
= W
k^
mT
gS
Weight
Temp
Swimming
Energetic losses due to egestion, excretion, andSDA are often modeled as constant fractionsof the energy taken in (consumed)
F = k
• C 1
U = k
2
• C
SDA = k
3
• C
Better understanding of complete energy budget:
G = C – {M + (F+U+SDA)}
Measured in lab,or estimatedwith models andfield observation
power andexponentialfunctions ofW, T, andS(wimming)
C = M + G + U + F Constantproportions of C
How have bioenergetic models
been used in fisheries?
Control of sea lamprey will result ina 5% increase in lake trout survivalHow much willrainbow smeltmortalityincrease?Calculate increase in trout biomass,then use bioenergetics to calculateincrease in consumption of rainbowsmelt
Sea Lamprey Control and Lake Trout
Rainbow smelt mortality willincrease by 3 percent
(La Bar 1993)
