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Bioenergetics: Calculating Energy Values in Food. Introduction. Energy is required by all animals to sustain life Sources : food, natural productivity, body stores (times of environmental stress or feed deprivation)

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  • Energy is required by all animals to sustain life
  • Sources: food, natural productivity, body stores (times of environmental stress or feed deprivation)
  • Lecture objectives: How much energy is needed by aquatic organisms?, How does it varies from terrestrials?, What are the sources, how is energy partitioned for various uses
lecture objectives
Lecture objectives
  • How much energy is needed by aquatic organisms?
  • How it varies from terrestrials?
  • What are the sources?
  • How is energy partitioned for various uses?
  • Lavoisier first demonstrated that oxidation of nutrients was some form of combustion (burning)
  • Rubner (1894) first demonstrated that fundamental Laws of Thermodynamics also applied to intact living animal systems
  • Organic matter  processes  CO2 + H2O + energy (released)
  • Understanding energy transforms is only possible when it is converted from one form to another
  • Energetics is the study of energy requirements and the flow of energy within systems
  • bioenergetics is the study of the balance between energy intake in the form of food and energy utilization by animals for life-sustaining processes
  • processes?: tissue synthesis, osmoregulation, digestion, respiration, reproduction, locomotion, etc.
  • the original energy source for food energy is the sun (See…I knew what I was talking about for once!)
  • energy from the sun is converted by photosynthesis into the production of glucose
  • glucose is the hydrocarbon source from which plants synthesize other organic compounds such as COH, protein, lipids
  • as previously mentioned, one must consider the quality of these sources
  • Animals are not heat engines
  • They can’t use the multitude of sources of energy we have (e.g., flywheels, falling objects, the tide, etc.)
  • Must obtain their energy from chemical bonds of complex molecules
  • How do they do it? In a nutshell, they oxidize these bonds to lower energy states using oxygen from the air
  • Trick: some bonds have more energy than others
  • most aquaculture animals obtain their energy from feeds
  • As mentioned, some bonds have more energy associated with them than others
  • when you have many nutrients comprising a feed, the energy level of that feed can vary substantially
  • availability of energy varies according to feed ingredient and species
  • growth is the endpoint of net energy
glycogen molecule
Glycogen Molecule

major COH storage form of energy

lipid molecule
Lipid Molecule

another major storage form

introduction cont
Introduction (cont.)
  • Energy goes through many cycles and transformations, always with loss of heat
  • can be released at various rates: gasoline can exploding vs. compost pile
  • nutritional energetics involves the study of the sources and transformations of energy into new products (mainly we are concerned with growth or tissue deposition)
  • of all dry matter we consume, 70-90% goes to synthesis of new products
energy forms
Energy Forms
  • Matter and energy are basically the same
  • it is often convenient to consider energy a property of matter (kcal/g feed)
  • nutritive value of food items is often reflected by calories
  • what you are used to seeing in the store is not calories, but kilocalories (kcal’s), or Calorie
  • common form of energy in the cell is ATP
energy forms1
Energy Forms
  • All processes in the animal body involve changes in energy
  • the word “energy” was first introduced in 1807, and defined as “ability to work”
  • found in many forms: heat, kinetic, electromagnetic, radiant, nuclear and chemical
  • for our purposes, chemical energy is the most important (e.g., ATP)
heat energy
Heat Energy
  • The measurement of energy requires converting it from one form to another
  • what we typically measure is heat (why?)
  • according to the first law of thermodynamics, all forms of energy can be converted quantitatively into heat energy
  • heat energy is represented by the various constituents of the diet
heat energy1
Heat Energy
  • however, the body is not a heat engine, heat is an end product of reactions
  • it is only useful to animals to keep the body warm
  • chemical reactions either generate heat (+H) or require heat (- H)
units of heat energy
Units of Heat Energy
  • The basic unit of energy is the calorie (cal)
  • it is the amount of heat required to raise the temperature of 1g of water 1 degree Celsius (measured from 14.5 to 15.5oC)
  • it is such a small unit, that most nutritionists prefer to use the kcal (or 1,000 calories)
  • REM:the kcal is more common (supermarket Calories)
other units of heat energy
Other Units of Heat Energy
  • BTU (British Thermal Unit) = amount of heat required to raise 1 lb of water 1oF
  • international unit: the joule - 1.0 joule = 0.239 calories or 1 calorie = 4.184 joule
  • a joule (J) is the energy required to accelerate a mass of 1kg at a speed of 1m/sec a distance of 1m
energy terms from de silva and anderson
Energy Terms (from De Silva and Anderson)
  • Energy flow is often shown as a diagram: every text has its own idea of a suitable diagram:
energy terms
Energy Terms
  • Gross energy (GE): energy released as heat resulting from combustion (kcal/g)
  • Intake Energy (IE): gross energy consumed in food (COH, lipid, protein)
  • Fecal Energy (FE): gross energy of feces (undigested feed, metabolic products, gut epithelial cells, digestive enzymes, excretory products)
  • Digestible Energy (DE): IE-FE
energy terms cont
Energy Terms (cont.)
  • Metabolizable energy (ME): energy in the food minus that lost in feces, urine and through gill excretion:

ME = IE - (FE + UE + ZE)

  • urinary energy (UE): total gross energy of urinary products of unused ingested compounds and metabolic products
  • gill excretion energy (ZE): gross energy of products excreted through gills (lungs in mammalian terrestrials), high in fish
  • surface energy (SE): energy lost to sloughing of mucus, scales, exoskeleton
energy terms cont1
Energy Terms (cont.)
  • Total heat production (HE): energy lost in the form of heat
  • heat lost is sourced from metabolism, thus, HE is an estimate of metabolic rate
  • measured by temperature change (calorimetry) or oxygen consumption rate
  • divided into a number of constituents
  • as per energy flow diagram 
energy terms total heat production
Energy Terms (total heat production)
  • Basic metabolic rate (HeE): heat energy released from cellular activity, respiration, blood circulation, etc.
  • heat of activity (HjE): heat produced by muscular activity (locomotion, maintaining position in water)
  • heat of thermal regulation (HcE): heat produced to maintain body temp (above zone of thermal neutrality)
  • heat of waste formation (HwE): heat associated with production of waste products
  • specific dynamic action (HiE): increase in heat production following consumption of feed (result of metab), varies with energy content of food, especially protein
energy utilization
Energy Utilization
  • Energy intake is divided among all energy-requiring processes
  • Magnitude of each depends on quantity of intake plus animal’s ability to digest and utilize that energy
  • Can vary by feeding mode: carnivorous vs. herbivorous

From Halver (page 7)

focus gross energy
Focus: Gross Energy
  • Energy content of a substance (i.e., food) is typically determined by completely oxidizing (burning) the compound to carbon dioxide, water and other gases
  • the amount of energy given off is measured and known as gross energy
  • gross energy (GE) is measured by a device known as a bomb calorimeter
gross energy of feedstuffs1
Gross Energy of Feedstuffs
  • Fats (triglycerides) have about twice the GE as carbohydrates
  • this is because of the relative amounts of oxygen, hydrogen and carbon in the compounds
  • energy is derived from the heat of combustion of these elements: C= 8 kcal/g, H= 34.5, etc.
  • typical heat from combustion of fat is 9.45 kcal/g, protein is 5.45, COH is 3.75
available energy
Available Energy
  • Gross energy only represents the energy present in dry matter (DM)
  • it is not a measurement of its energy value to the consuming animal!!
  • the difference between gross energy and energy available to the animal varies greatly for different foodstuffs
  • the key factor to know is how digestible the food item is
  • digestible energy also varies by species
digestible energy
Digestible Energy
  • The amount of energy available to an animal from a feedstuff is known as its digestible energy (DE)
  • REM: DE is defined as the difference between the gross energy of the feed item consumed (IE) and the energy lost in the feces (FE)
  • two methods of determination: direct or indirect
  • by the direct method, all feed items consumed and feces excreted are measured
digestible energy1
Digestible Energy
  • The indirect method involves only collecting a sample of the feed and feces
  • digestion coefficients are calculated on the basis of ratios of energy to indicator in the feed and feces
  • indicator?: an inert indigestible compound added to the feed
  • indicators: natural (fiber, ash) or synthetic (chromic oxide)
de calculations
DE Calculations

Direct Method

Feed energy - Fecal energy

% DE =

X 100

Feed energy

Indirect Method

Feed energy

Fecal indicator


% DE = 100 -


Fecal energy

Feed indicator

metabolizable energy
Metabolizable Energy
  • Even more detailed!
  • Represents DE minus energy lost from the body through gill and urinary wastes
  • More difficult to determine! Why?
  • REM: all urinary wastes in water!!! How do you collect that????

Intake energy - (E lost in feces, urine, gills)

%ME = -------------------------------------- x 100

Feed energy

metabolizable energy1
Metabolizable Energy
  • Use of ME vs DE would allow for a much more absolute evaluation of the dietary energy metabolized by tissues
  • however, ME offers little advantage over DE because most energy is used for digestion in fish
  • energy losses in fish through urine and gills does not vary much by feedstuff
  • fecal energy loss is more important
  • forcing a fish to eat involuntarily is not a good representation of actual energy processes
energy balance in fish
Energy Balance in Fish
  • Energy flow in fish is similar to that in mammals and birds
  • fish are more efficient in energy use
  • energy losses in urine and gill excretions are lower in fish because 85% of nitrogenous waste is excreted as ammonia (vs. urea in mammals and uric acid in birds)
  • heat increment (increase) as a result of ingesting feed is 3-5% ME in fish vs. 30% in mammals
  • maintenance energy requirements are lower because they don’t regulate body temp
  • they use less energy to maintain position
terrestrials vs aquatics
Terrestrials vs. Aquatics
  • This section concerns the requirements for energy by aquatic animals, how energy is partitioned, what it is used for and how it is measured
  • a major difference in nutrition between fish and farm animals is the amount of energy required for protein synthesis
  • protein synthesis refers to the building of proteins for tissue replacement, cell structure, enzymes, hormones, etc.
  • fish/shrimp have a lower dietary energy requirement
factors affecting energy partitioning
Factors Affecting Energy Partitioning
  • Factors either affect basal metabolic rate (e.g., body size) or affect other changes
  • those affecting BMR are the following:
  • body size:non-linear, y = axb, for most physiological variables, b values usually range between 0.7 and 0.8
  • oxygen availability: have conformers (linear) and non-conformers (constant until stressed)
o 2 consumption by size
O2 Consumption, by Size

(Fig. 2.1 from De Silva and Anderson)

factors affecting energy partitioning1
Factors Affecting Energy Partitioning
  • temperature: most aquaculture species are poikilotherms, significant effect, acclimation required, aquaculture situation may mean rapid temp changes
  • osmoregulation: changes in salinity result in increased cost of energy
  • stress: increased BMR resulting from heightened levels of waste, low oxygen, crowding, handling, pollution, etc. (manifested by hypoglycemia)
  • cycling: various animal processes are cyclic in nature (e.g., reproduction, migration)
factors affecting energy partitioning2
Factors Affecting Energy Partitioning
  • Those factors not affecting BMR are:
  • gonadal growth: most energy diverted from muscle growth into oogenesis, deposition of lipid, can represent 30-40% of body weight, implications????
  • locomotion: major part of energy consumption, varies due to body shape, behavior and size, aquatic vs. terrestrial issues
another index gross conversion efficiency k
Another Index: Gross Conversion Efficiency (K)
  • Referred to as “K”, often used as an indicator of the bioenergetic physiology of fish under various conditions
  • does not refer to an energy “budget”
  • measures growth rate (SGR) relative to feed intake over similar time periods
  • both factors are related to body size:
  • SGR = (ln Wtf-lnWti)/(Tf - Ti) x 100
  • RFI = (feed intake)/((0.5)(Wtf -Wti)(Tf-Ti))

K = (SGR/RFI) x 100

energy and growth
Energy and Growth
  • Dietary excesses or deficiencies of useful energy can reduce growth rate
  • this is because energy must be used for maintenance and voluntary activity before it is used for growth
  • dietary protein will be used for energy when the diet is deficient in energy relative to protein
  • when the diet contains excessive energy, feed intake is typically don’t want to be fat????
  • this also reduces intake of protein and other nutrients needed for growth
dietary sources of energy proteins
Dietary Sources of Energy:proteins
  • Considerable interaction between major nutrient groups as energy sources
  • protein can be used as an energy source
  • not typically used because of cost and use for protein synthesis (growth)
  • optimal ratio of protein:energy is around 22 mg PRO/kJ (45 kJ/g PRO; old info)
  • species variation: 17 (59) for tilapia, 29 (35)for catfish, 29 (34) for mutton snapper (Watanabe, et al., 2001);
  • digestibility variation
  • temperature variation
energy and growth1
Energy and Growth
  • Consumption of diets with low protein to energy ratios can lead to fat deposition (fatty acid synthetase)
  • this is undesirable in food fish because it reduces the dress-out yield and shortens shelf life
  • undesirable in shrimp due to build-up in hepato- pancreas (midgut), ultimately affecting cooking
  • low protein:energy diets can be useful for maturation animals, hatchery animals raised for release
energy requirments of fish
Energy Requirments of Fish
  • Determining the energy requirement of fish has been a difficult task, slow in coming
  • most research has been devoted to identifying protein requirements, major minerals and vitamins
  • in the past, feeds were formulated letting energy values “float”
  • excess or deficiency of nutritional energy does not often lead to poor health
energy requirements of fish
Energy Requirements of Fish
  • Further, if feeds are formulated with practical feedstuffs (ingredients), their energy levels are not likely to be off
  • it is really a matter of cost: protein is the most expensive component of the diet, COH sources are cheap, why use protein as an energy source????
  • In terrestrials, feed is consumed to meet energy requirements
  • thus, as energy level of the feed goes up, protein level is also designed to go up
energy requirements of fish1
Energy Requirements of Fish
  • This is because terrestrial animals are typically fed on an ad libitum basis
  • fish, on the other hand, aren’t fed this way
  • they are fed on a feed allowance basis (we estimate feed fed)
  • various studies have shown that the digestible energy (DE) requirement for channel catfish and carp was around 8.3-9.7 kcal DE/100 g fish/day
  • in terms of age, dietary level of DE and protein typically drop with age
energy requirements of fish2
Energy Requirements of Fish
  • DE and protein requirements typically follow each other, so the DE:P ratio (kcal/g) is fairly similar with age (if anything, a small increase)
  • this is partially due to the fact that fish grow faster when young (higher tissue turnover rate, demand for protein)
  • however, the influence of energy is stronger than that of protein relative to growth (Cuzon and Guillaume, 1997)
  • energy levels in crustacean diets usually range similar to those of fish
energy requirements of aquatics
Energy Requirements of Aquatics
  • The objective in formulating diets for most aquatic species is the same: finding a cheap energy source that is digestible and will spare protein
  • glucose is not acceptable in that it causes high blood sugar levels, poor growth, poor survival
  • complex dietary COH’s prove better
  • COH typically spares protein for growth
  • increase in dietary energy tends to increase performance when a diet low in protein is fed
energy problems
Energy Problems
  • Lipids and carbohydrates are typical energy sources for crustaceans
  • unfortunately, crustaceans are unable to tolerate diets having greater than 10% lipid (also hard to manufacture the feed!)
  • this means that the major energy source must be derived from COH
  • various COH are used to various degrees by crustaceans, making it difficult to calculate the true energy value of diets