Lecture 2: Bioenergetics

1. Lecture 2: Bioenergetics MARI-5314 September 4 and 11, 2003 Dr. Joe M. Fox CS-251

2. Introduction • A constant supply of energy is required by all animals to sustain life • Sources: feed eaten, natural productivity, body stores (times of environmental stress or feed deprivation) • 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

3. Introduction • Lavoisier first demonstrated that oxidation of nutrients was some form of combustion • 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

4. Introduction • 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.

5. Introduction • the original energy source for food energy is the sun • 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

6. Introduction • 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

7. Introduction • 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

8. Glycogen Molecule major COH storage form of energy

9. Lipid Molecule another major storage form

10. Introduction • 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

11. 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) • common form of energy in the cell is ATP

12. 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)

13. 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

14. 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)

15. 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) • the kcal is more common (it’s what you read in the supermarket as Calories)

16. 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

17. 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:

18. 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

19. 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

20. 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 

21. Energy Flow Diagram

22. 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

23. 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)

24. Focus: Gross Energy • Energy content of a substance 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 • other devices: gradient chamber, infra red detector

25. Gross Energy of Feedstuffs

26. 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 of combustion of fat is 9.45 kcal/g, protein is 5.45, COH is 3.75

27. 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

28. Digestible Energy • The amount of energy available to an animal from a feedstuff is known as its digestible energy (DE) • 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

29. 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)

30. DE Calculations Direct Method Feed energy - Fecal energy % DE = X 100 Feed energy Indirect Method Feed energy Fecal indicator x100 % DE = 100 - X Fecal energy Feed indicator

31. Metabolizable Energy • This is even more detailed distinction of energy availability • it represents DE minus energy lost from the body through gill and urinary wastes • much more difficult to determine • must collect all urinary wastes while fish is in water!!! Intake energy - (E lost in feces, urine, gills) %ME = -------------------------------------- x 100 Feed energy

32. 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

33. Energy Ratios for Rainbow Trout

34. 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

35. 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

36. 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)

37. O2 Consumption, by Size (Fig. 2.1 from De Silva and Anderson)

38. 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)

39. 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

40. 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

41. 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 reduced • this also reduces intake of protein and other nutrients needed for growth

42. 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

43. 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

44. 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

45. 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

46. 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

47. Protein, DE Requirements of Channel Catfish, by Age From Lovell, 1989

48. 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

49. Energy Requirements of Crustacea • The objective in formulating diets for most aquatic species is the same: finding a cheap energy source that is digestible and will spare protein • for shrimp, 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

50. Crustacean 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