Apparent Specific Dynamic Action Research Articles

Effects of waterborne cadmium exposure on growth performance, specific dynamic action, and energy budget of southern catfish Silurus meridionalis

This study investigated the effect of waterborne cadmium (Cd) exposure on the growth performance, specific dynamic action (SDA), and energy budget of southern catfish (Silurus meridionalis). S. meridionalis was exposed to various Cd concentrations (0–500 μg L−1) for 8 weeks. The specific growth rate (SGR), apparent digestibility, protein apparent digestibility, SDA parameters, and components of energy budgets were then determined. Compared to the control group, SGR was significantly reduced upon Cd exposure at 250 μg L−1 and 500 μg L−1. Compared to the control group, the experimental groups (62.5–500 μg L−1) showed significantly lower total feed intake and feed conversion efficiency. The apparent digestibility and protein apparent digestibility was significantly decreased in the 250 μg L−1 and 500 μg L−1 experimental groups compared to the control group. A significantly lower peak metabolic rate, SDA, and SDA coefficient were observed in the 250 μg L−1 and 500 μg L−1 experiment groups compared to the control group. The ratio of growth energy to assimilation energy in the 62.5–500 μg L−1 experimental groups was significantly lower than that of the control group. There was a significant increase in the ratio of metabolic energy to assimilation energy in Cd exposed groups compared to the control group. These results indicate that waterborne Cd exposure decreased the protein apparent digestibility, resulting in decreased SDA and SDA coefficient. Waterborne Cd exposure resulted in increased proportion of excretion energy and feces energy in S. meridionalis, whereas assimilation energy was reduced. Moreover, for assimilation energy, the energetic proportion for metabolism was increased, whereas the energetic proportion for growth was reduced

Metabolic costs of the mechanical components of the apparent specific dynamic action in the Dungeness crab, Cancer magister

The specific dynamic action (SDA) describes the postprandial increase in metabolism. It is a composite of mechanical and chemical digestion, nutrient transport and protein synthesis. How these individual events contribute to the overall SDA has not been worked out fully for any organism. The mechanical events associated with the SDA were investigated in Dungeness crabs, Cancer magister. Following consumption of a meal, oxygen consumption (MO2) remained elevated for several hours. When the crabs were presented with fish scent there was a 2 fold increase in MO2, which rapidly decreased once the stimulus was removed. Crabs were then offered fish in a perforated tube. There was a rapid increase in MO2 associated with handling which returned to pre-treatment levels within an hour of removal of the tube. Finally the crabs were fed a piece of foam that had been soaked in fish water to determine the costs of mechanical digestion. The mechanical breakdown of the meal accounted for 29.9±3.3% of the overall SDA. Since food handling produced a large increase in MO2, it was reinvestigated using crabs that had one or both claws removed. Although there were no statistically significant differences as a function of claw removal there was a consistent trend in the data. The maximum MO2, scope, duration and SDA increased from animals with 0 claws through 1 claw to 2 claws. The results showed that the mechanical portion of the SDA can account for a significant portion of the overall budget in decapod crustaceans.

Energetics of Byssus Attachment and Feeding in the Green-Lipped Mussel Perna canaliculus

In most animals, significant increases in metabolic rate are due to activity and to feeding (known as apparent specific dynamic action). We determined the energetic costs of activity and feeding in adult green-lipped mussels (Perna canaliculus). Maximal metabolic rate was determined, using closed-chamber respirometry, during byssus re-attachment, during specific dynamic action after 16 h of feeding with Isochrysis galbana, and for the two activities combined, in 23 mussels. Metabolic rate was significantly elevated above rest by about 1.9-fold during byssus attachment (17.1 ± 1.53 μg O(2) h(-1) g(-1) whole mussel wet weight at rest, increased to 27.9 ± 0.91 μg O(2) h(-1) g(-1)), and by 2.2-fold after feeding (31.4 ± 1.20 μg O(2) h(-1) g(-1)). Combined feeding and byssus attachment led to a still higher metabolic rate (34.0 ± 1.23 μg O(2) h(-1) g(-1)). Behavior was also significantly altered, with mussels being almost continuously open during attachment and after feeding (90%-99% of the time); however, the time spent open during the day decreased, reaching a minimum of 52% ± 9% 3 days after feeding, and remained low (67%-82%) for the following 45-day starvation period. Significant diurnal differences were observed, with mussels continuously (92%-100%) open at night. The key findings from this study are that green-lipped mussels (1) have an aerobic scope of approximately 2-fold; (2) reach a higher metabolic rate during feeding than during activity, and the two combined can raise the metabolic rate higher still; (3) display a marked diurnal behavior.

Juvenile salmon with high standard metabolic rates have higher energy costs but can process meals faster

Basal or standard metabolic rate (SMR) has been found to exhibit substantial intraspecific variation in a range of taxa, but the consequences of this variation are little understood. Here we explore how SMR is related to the energy cost of processing food, known as apparent specific dynamic action or the heat increment of feeding. Using juvenile Atlantic salmon Salmo salar, we show that fishes with a higher SMR had a higher peak and a greater total energy expenditure when digesting a given size of meal. However, the duration over which their metabolism was elevated after consuming the meal was shorter. The greater energy costs they incur for processing food may be related to their assimilation efficiency. These relationships are likely to have implications for feeding strategies and growth rates, since individuals with a higher SMR have higher routine costs of living but recover more quickly following feeding and so may have a greater potential for processing food.

The energetics of Calanus euxinus: locomotion, filtration of food and specific dynamic action

The effect of locomotor activity on respiration rate was studied in the food-deprived copepod Calanus euxinus tethered to a force sensor. The power generated by mouth appendages during cruising locomotion, with a frequency of 40 Hz, accounted for 0.026 and 0.0031 W for metabolic and mechanical processes, respectively. To overcome total hydrodynamic drag during foraging with a mean swimming speed of 3.2 cm s -1 , the copepods need 0.4 10 -3 W, equating to 1.3% of total metabolism. The losses of mechanical energy for body propulsion amounted to 1.3 10 -3 W, whilst the cost of feeding current generation run up to 1.8 10 -3 W, or 58% of the total. Changing of locomotor activity and respiration rate during feeding was examined separately in tethered and free-swimming copepods. At algal concentration of about 300 µgC L -1 the magnitude of specific dynamic action (SDA) averaged 1.2±0.44 nL O2 µgC -1 h -1 in copepodites V and females, with similar moving activity before and during feeding. The contribution of SDA into total metabolism varied from 23 to 85% in C. euxinus with low activity level and constituted only 10% in active animals. In starved copepods, with low locomotor activity, feeding events stimulated the increase in frequency and total duration of locomotion which resulted in elevated energy expenditure enhancing the “apparent SDA”.

The relationship between specific dynamic action and otolith growth in pike

The hypothesis was tested that the daily increment width (IW) of the otolith comprises two components, one that correlates with basal metabolic rate (as has been demonstrated previously) and the other that correlates with apparent specific dynamic action (Rsda)(the post‐prandial elevation in metabolism). Simultaneous measurements of IW and metabolic rate before and after a meal were collected from individual pike Esox lucius. After feeding, IW and metabolic rate increased above basal levels for 5–6 days. There was no correlation between daily IW and Rsda, reflecting within‐individual difference in the shapes of the post‐prandial responses of the two variables. There was a significant relationship between the total changes of IW and metabolic rate integrated following meals. The magnitude of the post‐prandial response as a proportion of the basal level was larger for metabolic rate than IW, mirroring the previously reported responses of these variables to acute temperature change. This study suggests that analysis of IW has the potential to provide a historic record of energy intake but only when integrated over a period equivalent to the digestion time. Consideration of energy budget theory indicates that IW is unlikely to provide a robust record of short‐term somatic growth if activity metabolism is significant and variable.

The effects of body mass and feeding on metabolic rate in small juvenile Atlantic cod

Apparent specific dynamic action (SDA) amplitude in young juvenile Atlantic cod Gadus morhua (1 to 8 g wet mass), fed a standardized meal and then exercised in a circular swimming respirometer at a constant swimming speed of 0·5 ± 0·3 body lengths s-1, occurred within l h after feeding in all juveniles. SDA amplitude were 1·4 to 1·8 times higher in fed fish compared to unfed fish, and rates of oxygen consumption decreased as body mass increased. SDA duration had a tendency to decrease with increasing body mass and was shortest, at 6 h, in the smallest fish (1–1·5 g), but increased to 10–11 h in the largest fish. Apparent SDA in fed fish (Rr) scaled with a mass exponent of 0·89, while maximum metabolic rate (Rmax) determined by chasing fish to exhaustion and then measuring oxygen consumption for 12 h, and unfed routine metabolic rate (Rr) scaled with a mass exponent of 0·79 and 0·76 respectively. Relative aerobic scope (Rmax– unfed Rr) did not appear to vary over the 1 to 8 g increase in wet mass. These results show that as body mass increased in young juvenile Atlantic cod: (1) apparent SDA (Rf) increased more rapidly than Rmax, and (2) apparent SDA took up >98% of the relative aerobic scope and that young Atlantic cod allocated most of the energy to growth, and left little for other metabolic activities.

The effects of body mass and feeding on metabolic rate in small juvenile Atlantic cod

Apparent specific dynamic action (SDA) amplitude in young juvenile Atlantic cod Gadus morhua (1 to 8 g wet mass), fed a standardized meal and then exercised in a circular swimming respirometer at a constant swimming speed of 0·5 ± 0·3 body lengths s‐1, occurred within l h after feeding in all juveniles. SDA amplitude were 1·4 to 1·8 times higher in fed fish compared to unfed fish, and rates of oxygen consumption decreased as body mass increased. SDA duration had a tendency to decrease with increasing body mass and was shortest, at 6 h, in the smallest fish (1–1·5 g), but increased to 10–11 h in the largest fish. Apparent SDA in fed fish (Rr) scaled with a mass exponent of 0·89, while maximum metabolic rate (Rmax) determined by chasing fish to exhaustion and then measuring oxygen consumption for 12 h, and unfed routine metabolic rate (Rr) scaled with a mass exponent of 0·79 and 0·76 respectively. Relative aerobic scope (Rmax– unfed Rr) did not appear to vary over the 1 to 8 g increase in wet mass. These results show that as body mass increased in young juvenile Atlantic cod: (1) apparent SDA (Rf) increased more rapidly than Rmax, and (2) apparent SDA took up >98% of the relative aerobic scope and that young Atlantic cod allocated most of the energy to growth, and left little for other metabolic activities.

Integrated physiological responses to feeding in the blue crab Callinectes sapidus.

The passage of a barium meal (15 % by mass) was followed through the digestive system of the blue crab Callinectes sapidus by flash-freezing crabs at set intervals, followed by radiography of specimens. Food moved from the oesophagus into the stomach region within 15 min. After 1-2 h, food was visible in the midgut, at 6 h it had reached the hindgut, and material was still present in the stomach at this time. The stomach was emptied between 8 and 10 h after feeding, and the entire digestive system was cleared of material after 18 h. A pulsed-Doppler flowmeter was used to monitor cardiac variables and arterial haemolymph flows during a 4 h control and 24 h postprandial period. Heart rate increased immediately upon food detection and remained elevated for 16-18 h after food ingestion. There was no significant change in stroke volume of the heart, and total cardiac output increased significantly and remained elevated above pre-feeding levels for 24 h after feeding. There was no change in haemolymph flow through the anterior or posterior aorta, but flow increased in the sternal, anterolateral and hepatic arteries. These changes in haemolymph flow reflected the use of the chelae and mouthparts in feeding, contraction of the visceral muscle surrounding the gut system and mobilisation of enzymes from the hepatopancreas. There was also a postprandial increase in the rate of oxygen uptake (apparent specific dynamic action). The rate of oxygen consumption (M(dot)(O2)) reached maximal levels 4 h after feeding and decreased slowly thereafter, reflecting the increased use of oxygen in digestion and absorption.

Effect of feeding frequency, feeding level and temperature on energy metabolism in Sparus aurata

The influences of temperature, ration size and food distribution on the energy metabolism of Sparus aurata were studied by monitoring oxygen consumption. For each factor combination rates of oxygen consumption (Rmean) were partitioned into components, representing resting rates (Rrest) and apparent specific dynamic action rates (Rsda). Maximal hourly rates (Rpeak) were also determined. Feeding led to an increase in oxygen consumption rates which lasted for approximately 37–39 h, with a peak between 1 and 6 h after feeding. The exact time course of the change in oxygen consumption was dependent on temperature, ration size and food distribution. An increase in food intake led to a rise in Rmean, Rsda and Rpeak but not Rrest. For a given ration level, an increase in temperature led to an increase in Rmean, Rrest, Rpeak and Rsda and in the fraction of food energy allocated to metabolism, but did not alter the distribution of such energy into maintenance needs and apparent specific dynamic action (SDA) effects.

Specific dynamic action and the metabolism of the brachyuran land crabs Ocypode quadrata (Fabricius, 1787), Goniopsis cruentata (Latreille, 1803) and Cardisoma guanhumi Latreille, 1825

Oxygen uptake (MO 2) was measured in the terrestrial crabs Ocypode quadrata (Fabricius, 1787), Goniopsis cruentata (Latreille, 1803) and Cardisoma guanhumi Latreille, 1825 as a function of digestive state to determine the magnitude and time course of specific dynamic action (SDA). Following 5 days of feeding ad libitum on fish flesh, “steady-state” MO 2 was about 2.8, 1.0 and 1.6 μm·g −1·h −1 in Ocypode(29–31 °C), Goniopsis (23–25°C) and Cardisoma (29–31 °C), respectively. After 5 days of fasting, “steady-state” MO 2 was decreased greatly to 1.0 and 0.5 μm·g −1·h −1 in Ocypode and Cardisoma, respectively, but was not significantly changed from feeding values in Goniopsis. Time-course experiments indicated that the peak in MO 2 following a single large meal occurred within 8 h in both Ocypode and Cardisoma. The apparent SDA persisted for longer than 50 h in Cardisoma, but less than 42 h in Ocypode. These data show that an apparent SDA of large magnitude and variable time course can occur in land crabs. However, the absence of any apparent SDA effect in Goniopsis indicates that it is not a necessary accompaniment to feeding in all terrestrial brachyurans, and must be verified on a species-by-species basis.

Apparent specific dynamic action of food in the grass shrimp, Penaeus monodon fabricius

1. 1. The influence of feeding on the oxygen consumption of Penaeus monodon was studied under controlled laboratory conditions. 2. 2. The shrimp adapted quickly to the experimental conditions as indicated by the short period (6–8 hr) required for their oxygen consumption to stabilize. 3. 3. Night-time oxygen consumption rates of the shrimps were significantly higher than those of the day-time. 4. 4. After feeding, the oxygen consumption of P. monodon increased (up to 512%, mean: 115 ± 90%) from the prefeeding level. 5. 5. Apparent specific dynamic action (SDA) ranged from 2.0 to 19.5% (mean: 9.1± 4.7%) and was not influenced by salinity. A significant portion of the energy ingested by a shrimp is therefore lost as apparent SDA. 6. 6. The increase in routine oxygen consumption associated with dark periods and feeding emphasize the importance of sufficient dissolved oxygen in production ponds during the night and when the shrimps are being fed. Sufficient dissolved oxygen during these periods would therefore improve production.

Bioenergetics of fishes in a high-energy surf-zone

Energy budgets are proposed for four teleost and two elasmobranch species as well as for the main icthyofauna groups for a surf-zone ecosystem. The ecology of surf-zone fishes of eastern Cape beaches, Algoa Bay South Africa, is reviewed. Using the equationC=F+U+R d +R R +ΔB, the following general energy budgets were derived for fishes: teleosts − 100=10+4+21+23+42; elasmobranchs − 100=11+2+16+24+48; whereC: food consumption;F: faeces;U: nonfaecal excretion;R d : apparent specific dynamic action;R R : routine metabolism;ΔB: growth. These show that most of the energy consumed is used in metabolism (R d +R R ) and growth (ΔB) whereas excretion (U) only accounts for a small portion. The energy budgets developed are within ranges recorded for other species. The main feeding groups of surf-zone icthyofauna are the southern mulletLiza richardsonii, the sandsharkRhinobatos annulatus, benthic feeders, zooplankton feeders, omnivorous and piscivorous fish with biomass values of 1000, 1000, 3000, 2400, 400 and 400 kJ m−1, respectively; and annual consumption budgets of 22107, 13725, 65710, 65476, 9758 and 8517 kJ m−1 yr−1, respectively.L. richardsonii feeds mainly on surf diatoms, consuming 0.5% of total diatom production. Zooplankton production supplies 91%, and macrobenthic production 9%, of the energy needs of other non-piscivorous carnivorous fishes. Piscivorous fishes consume 30% of the available fish production. Nonfaecal-energy production (8229 kJ m−1 yr−1) is utilised by surf diatoms, and faecal-energy production (30 341 kJ m−1 yr−1), is returned to the detritus pool to be utilised by the microbial loop in surf-waters. Our current knowledge of surf-zone energetics indicates that fishes are important predators. This study confirms the concept that the ecosystem generates adequate food for the fish assemblage. Fishes recycle energy, as excretory products, via the detritus pool and surf-diatoms, while fishes moving across the outer boundary of the surf-zone export energy from the system. Data presented, therefore, also support the general concept of a self-sustaining beach/surf-zone ecosystem.

Specific dynamic action (SDA) in the supralittoral isopod, Ligia pallasii: Identification of components of apparent SDA and effects of dietary amino acid quality and content on SDA

1. 1. Specific Dynamic Action (SDA) effects of diet were investigated in the supralittoral isopod, Ligia pallasii, using defined chemical diets. 2. 2. “Apparent SDA”, or the total rise in metabolic rate following a meal, was resolved in animals eating a nutritionally complete chemical diet into three components: 8% mechanical costs of moving food through the gut, 40% “excitement costs” due to investigator disturbance and presence of food, and 52% SDA. 3. 3. Excitement costs in animals exposed to food but which chose not to eat showed non-significant variation between diets containing different levels of chemical nutrients, but were significantly less on a diet containing only cellulose and agar. 4. 4. SDA increased with increasing concentration of amino acids in the diet. 5. 5. Substitution of whole-protein casein for free amino acids in the diet had no significant SDA effect, while substitution of free amino acids in the ratio found in casein more than doubled the SDA effect. 6. 6. Deletion of alanine from the diet caused no significant effect on SDA, while deletion of phenylalanine caused a highly significant elevation in SDA.

Aerobic metabolic scope and swimming performance in juvenile cod, Gadus morhua L.

Juvenile cod (Gadus morhua) were made to swim in a tunnel respirometer to determine the oxygen consumption during swimming at different speeds. Results were compared with measurements of standard and active metabolic rates in static respirometers before and after intense exercise. The oxygen consumption at maximum sustainable swimming speed was considerably lower than the peak oxygen consumption following exhausting exercise. It is suggested that these fish have a poorly developed system of aerobic (red) locomotor muscles which do not normally make a major demand upon oxygen consumption. Apparent specific dynamic action following feeding and repayment of oxygen debt following anaerobic exercise can each give rise to greater rates of oxygen consumption. Following exhausting exercise there is a delay of about 1 h before oxygen consumption reaches a peak level some 40% higher than the peak level observed during sustained swimming.

The impact of depressed pH and elevated aluminum concentrations on specific dynamic action in Somatochlora cingulata (De selys)

Differences in oxygen consumption attributable to apparent specific dynamic action (SDA) were measured in relation to feeding level in the dragonfly naiad Somatochlora cingulata exposed to low pH and sublethal aluminum concentration plus low pH. The average increases in respiration among the treatments following feeding were 50–60% that of controls. The average treatment peak height ratios (post/prefeeding respiration rates) were proportionately reduced and not significantly different from the average controls indicating that the resting metabolism, rather than SDA, was reduced.

Apparent specific dynamic action (SDA), fish weight and level of caloric intake in largemouth bass, Micropterus salmoides Lacepede

Apparent SDA (specific dynamic action) in largemouth bass ( Micropterus salmoides) was equated to the oxygen uptake associated with a meal of a dry pelleted diet (35.8% protein). Apparent SDA, maximum rate of oxygen uptake, and the length of time that the rate of oxygen uptake remained elevated above the prefeeding level were measured in relation to energy ingested (5–150 cal g −1) and fish weight (5–250 g). Apparent SDA was positively related to energy intake, but for a given energy intake it was negatively related to bass weight. When expressed relative to energy intake, the mean apparent SDA of the dry pelleted diet represented 11.3% ± 1.32 (95% confidence limits). Maximum oxygen uptake following a meal was positively related to energy ingested and to fish weight. In bass smaller than 100 g and fed to satiation, oxygen uptake equalled the active rate. The length of time (12 to 76 h) that the rate of oxygen uptake remained elevated was positively related to energy ingested and negatively related to bass weight. The observations in the present study are discussed with reference to natural diets and to other studies where growth and food conversion efficiency were measured.

An energy budget for juvenile thick‐lipped mullet, Crenimugil labrosus (Risso)

A series of experiments were carried out to construct an energy budget for juvenile thick lipped mullet, Crenimugil labrosus Risso. A partial factorial experimental design was used to examine the effects of temperature, fish size and meal size on growth. The maximum ration that the fish were able to ingest completely per day was found to be 0·8, 1·4 and 2·3% wet body weight (b.w.) at 13,18 and 23°C, respectively. Ingested maintenance requirements (M.R.) were estimated to be 137, 205 and 288 cal fish‐1 day‐1 at 13, 18 and 23°C, respectively. At 18deg; C, M.R. varied as 25 W1.04 cal day‐1, where W= fish weight (g). Growth rate increased with increasing temperature. Maximal conversion efficiency was 21–24% and was achieved closer to the maximum ingested ration with increasing temperature.The relationship between respiration rate and W at 18deg; C for 3‐20 g fish is described by: respiration rate (ml O2 h‐1) = 0·128 W0.976The energy cost of apparent specific dynamic action at 18deg; C was found to vary between 5·1% and 23·6% of the calorific value of the ingested meal (1% wet b.w.), mean (± S.E.)=10·2 ± 2·0%.Post mortem analyses of groups of fish fed 0·2, 0·8 and 1·5% wet b.w. meals showed a significant increase in total lipid and a significant decrease in water content with increasing ratio size. A negative correlation was found between body water content and total lipid (and calories).The mean assimilation efficiency (±s.e.) for 5–10 g mullet at 18deg; C was 73·9 ± 3·6%.The observations reported in this study were brought together to construct an energy budget for juvenile C. labrosus which was found to give a reliable prediction (within 10%) of energy demand and growth under the prevailing experimental conditions. Both gross (K1) and net (K2) growth efficiencies, based on energy values, increased with increasing ratio size up to satiation and were independent of temperature. The maximum values of K1 and K2 observed were 0·33 and 0·46, respectively. The third order efficiency (K3) appeared to be independent of temperature and ration size; mean values ranged between 0·66 and 0·84.

Specific Dynamic Action and Diet in Largemouth Bass, Micropterus salmoides (Lacépède)

Apparent specific dynamic action (SDA) in largemouth bass (5-28 g) was equated to oxygen uptake subsequent to the ingestion of a meal. The effects of six diets on apparent SDA were investigated, one balanced or standard diet and five consisting of different proportions of protein and carbohydrate. Apparent SDA was positively related to gross energy ingested and to the level of dietary protein. For a given energy intake, apparent SDA was highest and lowest for diets of 100% protein and 100% carbohydrate, respectively. Evidence of a protein-sparing effect was found when the carbohydrate component represented 25% of the diet and the energy intake was less than 0.8 kcal. Apparent SDA was divided into mechanical SDA, the energy cost for the physical processing of food, and biochemical SDA, the energy cost of anabolic and catabolic processes associated with a meal. Biochemical SDA increased with energy ingested irrespective of diet and was higher by approximately an order of magnitude when bass were fed 1.5 kcal of a 100% protein diet than when fish received an isocaloric meal of 100% carbohydrate. Rate of oxygen uptake following feeding remained above the prefeeding level for 12-72 hours depending on diet and energy ingested.

Mechanical and biochemical components of apparent specific dynamic action in largemouth bass, Micropterm salmoides Lacéepède

Apparent SDA was defined as the energy expenditure associated with the ingestion of a meal. In the present study apparent SDA was equated to an increase in oxygen consumption above the postabsorptive level subsequent to the ingestion of a meal. The energy cost for physically processing a meal, mechanical SDA, was equated to the oxygen uptake associated with the ingestion of non‐digestible cellulose. The energy utilized by anabolic and catabolic processes associated with the ingestion of a standard diet was identified as biochemical SDA. Apparent, mechanical and biochemical SDA were each positively related to the energy intake of the standard diet. Apparent SDA expressed relatively to energy ingested equalled 10·5% and was independent of the caloric content of the meal. Mechanical SDA increased asymptotically with ingested meal size and energy content. Relative to apparent SDA, mechanical SDA decreased with meal size, suggestive of an enhancement in efficiency. Biochemical SDA rose exponentially with increase in ingested energy, reflective of the cost for growth and catabolism.