Specific Dynamic Action Coefficient Research Articles

SDA coefficient is temperature dependent in rainbow trout (Oncorhynchus mykiss, Walbaum 1792) in a practical approach using group respirometry.

Rising global temperatures have raised the need for detailed knowledge of the effects of rising temperatures on the physiology of animals used in aquaculture. Here we used a multifactorial bioenergetic approach using groups of rainbow trout (Oncorhynchus mykiss) with an average single fish weight of 183.75g±0.65g to investigate the interactions of feeding and temperature with key metabolic variables. We used a recirculating aquaculture respirometry system (RARS) to test three ration sizes (0.65; 0.975; 1.3% of live body weight (BW)) over a range of three consecutive temperatures (14; 17; 20°C). The fish were fed once per day for 6days at each temperature and subsequently starved for 5days to return to standard metabolic rate (SMR). This study aimed to answer the highly discussed topic of the temperature dependency of key metabolic specific dynamic action (SDA)-variables SDAcoef and SDAdur. We were able to provide evidence, that in rainbow trout the SDAcoef is highly dependent on the environmental temperature in the first ever approach to assess these variables in a group respirometer with this species. We compared the results of this study with a sophisticated bioenergetic model by Elliot and Hurley (2002) and thereby provide evidence for the practicability of group respirometry as a method to assess bioenergetic data under culture like conditions.

Effect of meal size on the postprandial metabolic response in Chinese giant salamander Andrias davidianus larvae

The digestive physiological characteristics of Chinese giant salamander Andrias davidianus have not been reported in the existing literature, and improving our knowledge in this area could help in the artificial culture of the species. The effect of meal size on the specific dynamic action (SDA) of A. davidianus larvae was assessed in this study at a water temperature of 20°C. The Chinese giant salamander was fed by test diets at meal sizes of 0.5, 1, 2, 4, 8 and 12% of its body mass (4.41 ± 0.07 g), and the postprandial oxygen consumption rate (MO2) was measured at 2 h intervals until the rate returned to its preprandial level. Peak MO2 (MO2peak) increased with meal size but levelled off at larger meal sizes within the studied range (8-12% body mass). The factorial metabolic scope increased from 1.27 to 2.11 when meal size increased from 0.5 to 12%. Time to reach MO2peak was not affected by the relative meal size. The SDA duration increased from 8.89 to 47.33 h as the relative meal size increased from 0.5 to 12%. The amount of energy expended during SDA increased linearly with increasing meal size (R2 = 0.842, p < 0.001, n = 60). There was no significant difference in the SDA coefficient among the different relative meal size groups. These data suggest that (1) A. davidianus larvae increase their energy demands during digestion by prolonging the SDA duration rather than increasing the MO2peak as meal size increases, and (2) A. davidianus showed a smaller factorial metabolic scope in the process of digesting large meal sizes, which may be related to the limited MO2peak of the species.

Energetic savings when switching from a whole-fish type diet to a commercial pelleted diet in California yellowtail (Seriola dorsalis)

Feed is one of the largest costs in most aquaculture operations, and as such, aquaculturists are continually striving to improve on ingredient sourcing and formulations to increase growth and performance while reducing costs. Analysis of the energy expended in digestion of different feeds can be a valuable early indicator of the suitability of a new ingredient or formulation. We use respirometry, an activity level analysis, and proximate analysis of fecal samples to compare the metabolic cost of digestion in California yellowtail (Seriola dorsalis) fed two different diets – a meal of whole sardine fillets representing a whole fish diet and a commercial pelleted feed designed specifically for Seriola aquaculture.Respiration trials reveal that the specific dynamic action coefficient (SDACoefficient), SDA coefficient (SDACoefficient), or percent of energy expended on digestion in relation to the total energy available in a meal, was more than double for a whole-fish type meal (20.8 ± 0.1%) than for the pelleted meal (10.2 ± 0.8%). Analysis of fish activities indicated 12.3% greater activity during the whole-fish type meal, as compared with the pelleted meal. After 24 h, the total amount of protein and lipid remaining in the feces from the whole-fish type meal (4.2 ± 0.7 kJ, 2.2 ± 0.4 kJ respectively) was significantly higher than the pelleted meal (1.8 ± 0.2 kJ, 0.9 ± 0.2 kJ respectively). Digestibility of the whole-fish type meal was slightly lower than the pelleted meal at 95.3 ± 0.5% and 97.7 ± 0.2%, respectively.The reduction in the energetic cost of digestion observed in fish fed the commercial pellet diet is likely attributed to the additional processing during manufacture, which liberates a significant portion of the energy normally allotted towards digestion. The results of this work reveal and quantify the benefits of switching from whole-fish feed to a commercial compound feed, as the reduced energetic costs of digestion allow for greater amounts of energy to be available for somatic growth.

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

The effect of protein and lipid level on the specific dynamic action and post-prandial nitrogen excretion in subadult of white shrimp Litopenaeus vannamei

The study aimed to evaluate the effect of 4 levels of dietary protein (20, 30, 40 and 50%) and lipids (2, 4, 8 and 16%) on the magnitude and duration of specific dynamic action (SDA) and postprandial nitrogen excretion in the subadult white shrimp Litopenaeus vannamei using computer-controlled metabolic chambers (continuous-flow respirometer). We determined the oxygen consumption rate at 1 h intervals until the postprandial oxygen consumption rate returned to the pre-feeding level. Shrimp fed all the diets had significantly higher respiration rates after feeding due to the SDA. Oxygen consumption, the SDA coefficient and the SDA magnitude increased notably with increasing dietary protein content. Shrimp fed the 20% protein diet had the lowest levels of pre- and post-feeding respiration and the smallest SDA. A significant change in the SDA coefficient relative to each lipid level was not demonstrable. Additionally, nitrogenous excretion increased with an increase of dietary protein but not with an increase of lipid level. By estimating the SDA of subadults, the response to standard metabolic rate (SMR) was lower than that reported for juveniles and postlarva white shrimp

Limited Capacity for Faster Digestion in Larval Coral Reef Fish at an Elevated Temperature.

The prevalence of extreme, short-term temperature spikes in coastal regions during summer months is predicted to increase with ongoing climate change. In tropical systems, these changes are predicted to increase the metabolic demand of coral reef fish larvae while also altering the plankton communities upon which the larvae feed during their pelagic phase. The consequences of these predictions remain speculative in the absence of empirical data on the interactive effects of warm temperatures on the metabolism, postprandial processes and growth responses of coral reef fish larvae. Here, we tested the effect of increased temperature on the metabolism, postprandial performance and fine-scale growth patterns of a coral reef fish (Amphiprion percula) in the latter half of its ~11-d larval phase. First, we measured the length and weight of fed versus fasted larvae (N = 340; mean body mass 4.1±0.05 mg) across fine temporal scales at a typical current summer temperature (28.5°C) and a temperature that is likely be encountered during warm summer periods later this century (31.5°C). Second, we measured routine metabolic rate (Mo2 routine) and the energetics of the postprandial processes (i.e., digestion, absorption and assimilation of a meal; termed specific dynamic action (SDA)) at both temperatures. Larvae fed voraciously when provided with food for a 12-hour period and displayed a temperature-independent increase in mass of 40.1% (28.5°C) and 42.6% (31.5°C), which was largely associated with the mass of prey in the gut. A subsequent 12-h fasting period revealed that the larvae had grown 21.2±4.8% (28.5°C) and 22.8±8.8% (31.5°C) in mass and 10.3±2.0% (28.5°C) and 7.8±2.6% (31.5°C) in length compared with pre-feeding values (no significant temperature effect). Mo2 routine was 55±16% higher at 31.5°C and peak Mo2 during the postprandial period was 28±11% higher at 31.5°C, yet elevated temperature had no significant effect on SDA (0.51±0.06 J at 28.5°C vs. 0.53±0.07 J at 31.5°C), SDA duration (6.0±0.6 h vs. 6.5±0.5 h), or the percent of total meal energy used for SDA (SDA coefficient: 10.1±1.3% vs. 13.0±1.7%). Our findings of higher Mo2 routine but similar SDA coefficient at high temperature provide the first empirical evidence that coral reef fish larvae may have to secure more food to attain similar growth rates during warm summer periods, and perhaps with chronically warmer conditions associated with climate change.

The effect of temperature on postprandial metabolism of yellowfin tuna (Thunnus albacares)

Specific dynamic action (SDA), the increase in metabolic expenditure associated with consumption of a meal, represents a substantial portion of fish energy budgets and is highly influenced by ambient temperature. The effect of temperature on SDA has not been studied in yellowfin tuna (Thunnus albacares, Bonnaterre 1788), an active pelagic predator that occupies temperate and subtropical waters. The energetic cost and duration of SDA were calculated by comparing routine and post-prandial oxygen consumption rates. Mean routine metabolic rates in yellowfin tuna increased with temperature, from 136mgO2kg−1h−1 at 20°C to 211mgO2kg−1h at 24°C. The mean duration of SDA decreased from 40.2h at 20°C to 33.1h at 24°C, while mean SDA coefficient, the percentage of energy in a meal that is consumed during digestion, increased from 5.9% at 20°C to 12.7% at 24°C. Digestion in yellowfin tuna is faster at a higher temperature but requires additional oxidative energy. Enhanced characterization of the role of temperature in SDA of yellowfin tuna deepens our understanding of tuna physiology and can help improve management of aquaculture and fisheries.

Meal size effects on the postprandial metabolic response of Bothrops alternatus (Serpentes: Viperidae)

We examined the effects of meal size on the postprandial metabolic response of the lancehead Bothrops alternatus (Dumeril, Bibron & Dumeril, 1894), fed mice equaling to 5, 10, 20, and 40% of the snake's body mass. The maximum O 2 consumption rates measured during digestion increased with meal size, reaching levels up to 2.8-7.8-fold higher than the metabolic rate measured during fasting. Specific Dynamic Action (SDA) duration also increased with meal size, lasting from 54 to 212 hours to complete. Under our experimental conditions, 30°C, the majority of our snakes failed to completely digest prey with a relative size of 40%. The SDA coefficient ranged from 17 to 27% of the energy content of the meal and was not affected by meal size.

The effect of aerobic exercise training on growth performance, digestive enzyme activities and postprandial metabolic response in juvenile qingbo (Spinibarbus sinensis)

Continual swimming exercise usually promotes growth in fish at a moderate water velocity. We hypothesized that the improvement in growth in exercise-trained fish may be accompanied by increases in digestive enzyme activity, respiratory capacity and, hence, postprandial metabolism. Juvenile qingbo fish (Spinibarbus sinensis) were subjected to aerobic training for 8weeks at a water velocity of control (3cms−1), 1, 2 and 4 body length (bl)s−1 at a constant temperature of 25°C. The feed intake (FI), food conversion rate (FCR), specific growth rate (SGR), whole-body composition, trypsin and lipase activities, maximal oxygen consumption (M˙O2max) and postprandial M˙O2 response were measured at the end of the training period. Aerobic exercise training induced a significant increase in FI compared with the control group, while the FCR of the 4bls−1 group was significantly lower than for the other three groups (P<0.05). The 1 and 2bls−1 groups showed a significantly higher SGR over the control group (P<0.05). The whole-body fat and protein contents were significantly altered after aerobic exercise training (P<0.05). Furthermore, aerobic exercise training elevated the activity of both trypsin and lipase in the hepatopancreas and intestinal tract of juvenile S. sinensis. The M˙O2max of the 4bls−1 training group was significantly higher than for the control group. The resting M˙O2 (M˙O2rest) and peak postprandial M˙O2 (M˙O2peak) in the three training groups were significantly higher than in the control group (P<0.05). Time to M˙O2peak was significantly shorter in the 1, 2 and 4bls−1 training groups compared with the control group, while exercise training showed no effect on SDA (specific dynamic action) duration, factorial metabolic scope, energy expended on SDA and the SDA coefficient when compared to the control group. These data suggest that (1) the optimum water velocity for the growth of juvenile S. sinensis occurred at approximately 2.4bls−1; (2) the improvement of growth may have been primarily due to an increase in the FI after long-term training; (3) and aerobic exercise training boosted the activity of digestive enzymes and maximum digestive metabolism, which could favor fast digestion and growth in juvenile S. sinensis.

Effect of meal size on postprandial metabolic response and excess post-exercise oxygen consumption in juvenile rock carp (Procypris rabaudi)

To investigate the effect of meal size on postprandial metabolic response and excess post-exercise oxygen consumption(EPOC) in juvenile rock carp(Procypris rabaudi)[(13.05±0.17) g,n=44],experimental fish were lightly anaesthetized and force-fed with compound feed(meal sizes: 0%,0.5%,1% and 2% body weight) at(25 ±0.5)℃.After diet offered,oxygen consumption rates at different intervals were measured.Variables of postprandial metabolic and EPOC responses were calculated.The results of present study showed that resting metabolic rates(RMR) were not significantly different among all groups.The postprandial metabolic rate first increased and then slowly decreased to pre-fed level.The time to peak metabolic rate and the energy expended on Specific dynamic action(SDA) in 0.5% and 1% meal size groups were lower than that of 2% meal size group(P0.05).The peak metabolic rates(PMR) and the SDA coefficients were not significantly different among 0.5%,1% and 2% meal size groups.Pre-exercise metabolic rate in feeding group was significantly higher than that of fasting group(P0.05).Peak post-exercise metabolic rate,metabolic rate increment and excess post-exercise oxygen consumption magnitude were not significantly different between feeding group and fasting group.The maximum metabolic rate(MMR) and MMR/RMR were significantly higher than PMR and PMR/RMR(P0.05).The fish fulfilled the increased energy demand during digestive process by means of prolonged SDA duration with the increase of meal size.EPOC was not influenced by feeding in the fish.

Effect of meal size on the specific dynamic action of the juvenile snakehead (Channa argus)

The effect of meal size on the specific dynamic action (SDA) of the juvenile snakehead (Channa argus) was assessed at 25°C. The fish were fed with test diets at meal sizes of 0.5, 1, 2, 3, 4, and 5% body mass and the postprandial oxygen consumption rate was determined at 1-h intervals until it returned to the pre-prandial level. The peak metabolic rate increased from 237.4 to 283.2mgO2kg−1h−1 as the relative meal size increased from 0.5% to 3% and leveled off at 4% and 5%. Factorial metabolic scope increased from 1.53 to 1.99 and SDA duration increased from 11.7 to 32.3h as the relative meal size increased from 0.5% to 5%. The relationship between SDA duration (D) and relative meal size (M) was described as: D=4.28M+10.62 (r2=0.752, P<0.05, n=50). The energy expended on SDA increased while the SDA coefficient decreased with increasing meal size. The results of the present study suggest that the snakehead may adopt different feeding strategies when taking in different amounts of food.

Physiological mechanisms underlying a trade-off between growth rate and tolerance of feed deprivation in the European sea bass (Dicentrarchus labrax)

The specific growth rate (SGR) of a cohort of 2000 tagged juvenile European sea bass was measured in a common tank, during two sequential cycles comprising three-weeks feed deprivation followed by three-weeks ad libitum re-feeding. After correction for initial size at age as fork length, there was a direct correlation between negative SGR (rate of mass loss) during feed deprivation and positive SGR (rate of compensatory growth) during re-feeding (Spearman rank correlation R=0.388, P=0.000002). Following a period of rearing under standard culture conditions, individuals representing 'high growth' phenotypes (GP) and 'high tolerance of feed deprivation' phenotypes (DP) were selected from either end of the SGR spectrum. Static and swimming respirometry could not demonstrate lower routine or standard metabolic rate in DP to account for greater tolerance of feed deprivation. Increased rates of compensatory growth in GP were not linked to greater maximum metabolic rate, aerobic metabolic scope or maximum cardiac performance than DP. When fed a standard ration, however, GP completed the specific dynamic action (SDA) response significantly faster than DP. Therefore, higher growth rate in GP was linked to greater capacity to process food. There was no difference in SDA coefficient, an indicator of energetic efficiency. The results indicate that individual variation in growth rate in sea bass reflects, in part, a trade-off against tolerance of food deprivation. The two phenotypes represented the opposing ends of a spectrum. The GP aims to exploit available resources and grow as rapidly as possible but at a cost of physiological and/or behavioural attributes, which lead to increased energy dissipation when food is not available. An opposing strategy, exemplified by DP, is less 'boom and bust', with a lower physiological capacity to exploit resources but which is less costly to sustain during periods of food deprivation.

Effects of body lipid content on the resting metabolic rate and postprandial metabolic response in the southern catfish Silurus meridionalis

We assessed the effects of body lipid content on the resting metabolic rate and specific dynamic action (SDA) of the southern catfish Silurus meridionalis. Obese and lean fish were obtained by feeding the fish with two different feeds at 27.5 °C for 4 weeks prior to the experiment. The fish were fed with experimental diets with a meal size of 4% by body mass. A continuous-flow respirometer was used to determine the oxygen consumption rate at 2-h intervals until the postprandial oxygen consumption rate had returned to the preprandial level. The body lipid content of the obese fish was significantly greater than that of the lean fish. The metabolic parameters evaluated (resting metabolic rate, peak metabolic rate (R peak), factorial ratio, time to peak, duration, energy expended on SDA (SDA E), or SDA coefficient) were not significantly affected by body fat content in terms of the whole-body or mass-specific values. Increased body fat content did not decrease the resting metabolic rate in the southern catfish, which might be due to the higher levels of highly unsaturated fatty acids in these fish. The results also suggest that the body composition does not appear to affect the SDA response.

The effect of temperature and body weight on the routine metabolic rate and postprandial metabolic response in mulloway, Argyrosomus japonicus

Specific dynamic action (SDA) is the energy expended on the physiological processes associated with meal digestion and is strongly influenced by the characteristics of the meal and the body weight (BW) and temperature of the organism. This study assessed the effects of temperature and body weight on the routine metabolic rate (RMR) and postprandial metabolic response in mulloway, Argyrosomus japonicus. RMR and SDA were established at 3 temperatures (14, 20 and 26 °C). 5 size classes of mulloway ranging from 60 g to 1.14 kg were used to establish RMR with 3 of the 5 size classes (60, 120 and 240 g) used to establish SDA. The effect of body size on the mass-specific RMR (mg O 2 kg − 1 h − 1 ) varied significantly depending on the temperature; there was a greater relative increase in the mass-specific RMR for smaller mulloway with increasing temperature. No statistical differences were found between the mass exponent ( b) values at each temperature when tested against H 0: b = 0.8. The gross RMR of mulloway (mg O 2 fish − 1 h − 1 ) can be described as function of temperature ( T; 14–26 °C) as: (0.0195 T–0.0454)BW(g) 0.8 and the mass-specific RMR (mg O 2 kg − 1 h − 1 ) can be described as: (21.042 T–74.867)BW(g) − 0.2 . Both SDA duration and time to peak SDA were influenced by temperature and body weight; SDA duration occurred within 41–89 h and peak time occurred within 17–38 h of feeding. The effect of body size on peak metabolic rate varied significantly depending on temperature, generally increasing with temperature and decreasing with increasing body size. Peak gross oxygen consumption ( MO 2: mg O 2 fish − 1 h − 1 ) scaled allometrically with BW. Temperature, but not body size, significantly affected SDA scope, although the difference was numerically small. There was a trend for MO 2 above RMR over the SDA period to increase with temperature; however, this was not statistically significant. The average proportion of energy expended over the SDA period (SDA coefficient) ranged from approximately 7–13% of the total DE intake while the proportion of total energy expended on SDA above RMR ranged from approximately 16–27%.

Effects of temperature on the specific dynamic action of the southern catfish, Silurus meridionalis

Specific dynamic action (SDA), the energy expended on all physiological processes that is associated with meal digestion and assimilation, is strongly affected by temperature. We assessed the effects of temperature on the postprandial metabolic response and calculated SDA of the southern catfish, Silurus meridionalis. The fish was fed with experimental diets at a meal size of 4% body mass, and by using an 8-chamber, continuous-flow respirometer the oxygen consumption rate was determined at a 2 h interval until the postprandial oxygen consumption rate returning to the preprandial level, at four different temperatures. The energy expended on SDA (SDA(E)) were 2.71, 3.07, 3.16, and 3.62 kJ, the SDA(coefficients) (energy expended on SDA quantified as a percentage of the digestible energy content of the meal) were 7.70, 9.44, 10.36, and 11.12%, and the peak metabolic rates (R(peak)) of SDA were 3.48, 4.31, 5.96, and 7.30 mg O2 h(-1), at 17.5, 22.5, 27.5, and 32.5 degrees C respectively. The relationships between those parameters and temperature were: SDA(E)=1.74+0.0559T (n=26, r(2)=0.676), SDA(coefficient)=4.10+0.223T (n=26, r(2)=0.726), and R(peak)=-1.34+0.264T (n=26, r(2)=0.896). The SDA durations showed a slow-fast-slow tendency of decrease with increasing temperature, and were 88.00, 85.71, 67.71, and 66.50 h at 17.5, 22.5, 27.5 and 32.5 degrees C respectively. Two separate peaks appeared during the SDA response at 17.5 degrees C, and it might be due to a rapid startup of the process with a lag of the process, which suggested that the peaks of mechanical component and biochemical component of SDA might be separated when temperature was low enough.

The effect of ration size, temperature and body weight on specific dynamic action of the common cuttlefish Sepia officinalis

The effect of meal size (shrimp Crangon crangon) [0.83–18.82% dry body weight (Dw)] on specific dynamic action (SDA) was assessed in cuttlefish Sepia officinalis (1.03–6.25 g Dw) held at 15 and 20°C. Cuttlefish 2 g when given the same quantity of food. Handling, eating and digesting a shrimp meal was temperature dependent with cuttlefish processing and digesting a similar sized shrimp meal faster at 20°C than at 15°C. The proportional increase in oxygen consumption (2.07 ± 0.02) was not correlated with feeding rate (FR) and was independent of temperature and cuttlefish size. The SDA peak was not correlated with FRs, and increased as cuttlefish size and temperature increased. The mean SDA coefficient was 0.87 ± 0.07% of the ingested energy; one of the lowest SDA values recorded amongst vertebrates and invertebrates. Daily energy requirements (KJ day−1) for S. officinalis were calculated from laboratory estimates of energy losses due to standard (MO2 Standard), routine (MO2 Routine) and feeding (MO2 SDA) oxygen consumption. Laboratory estimates of daily metabolic expenditures were combined with results from previous investigations to construct an energy budget for 1 and 5 g cuttlefish consuming a meal of 5 and 15% Dw at 20°C and the amount of energy available for growth was estimated to be between 35 and 80.3% of the ingested energy.

Specific dynamic action in two body size groups of the southern catfish (Silurus meridionalis) fed diets differing in carbohydrate and lipid contents

Specific dynamic action (SDA), the energy costs associated with meal digestion and assimilation, is generally affected by body size and food composition. We assessed the postprandial metabolic response and calculated SDA in two size groups of the southern catfish (Silurus meridionalis), each fed one of two diets, high lipid or high carbohydrate, at a meal size of 4% the body mass. Using a continuous-flow respirometer, we determined the oxygen consumption rate at 2-h intervals until the postprandial oxygen consumption rate returned to the prefeeding level. None of the parameters (resting metabolic rate, Rpeak, factorial ratio, time-to-peak, duration, energy expended on SDA, or SDA coefficient) were significantly affected by diet nor was there an interaction between diet and body mass. Rpeak and energy expended on SDA for the whole fish body were significantly higher in the larger fish than the smaller one in both dietary treatments, whereas no significant effect of body size was found in mass specific values. Factorial ratio (range 3.41 to 3.60), peak time (range 9.6 to 12.7 h), SDA coefficient (range 9.36 to 10.36%), and SDA duration (range 62.0 to 71.0 h) did not significantly differ between body size groups. These results suggest that in S. meridionalis the percentage of assimilated energy allocated to SDA may be independent of the body mass.

Effects of temperature on the specific dynamic action of the southern catfish, Silurus meridionalis

Specific dynamic action (SDA), the energy expended on all physiological processes that is associated with meal digestion and assimilation, is strongly affected by temperature. We assessed the effects of temperature on the postprandial metabolic response and calculated SDA of the southern catfish, Silurus meridionalis. The fish was fed with experimental diets at a meal size of 4% body mass, and by using an 8-chamber, continuous-flow respirometer the oxygen consumption rate was determined at a 2 h interval until the postprandial oxygen consumption rate returning to the preprandial level, at four different temperatures. The energy expended on SDA (SDA E) were 2.71, 3.07, 3.16, and 3.62 kJ, the SDA coefficients (energy expended on SDA quantified as a percentage of the digestible energy content of the meal) were 7.70, 9.44, 10.36, and 11.12%, and the peak metabolic rates ( R peak) of SDA were 3.48, 4.31, 5.96, and 7.30 mg O 2 h − 1 , at 17.5, 22.5, 27.5, and 32.5 °C respectively. The relationships between those parameters and temperature were: SDA E = 1.74 + 0.0559 T ( n = 26, r 2 = 0.676), SDA coefficient = 4.10 + 0.223 T ( n = 26, r 2 = 0.726), and R peak = − 1.34 + 0.264 T ( n = 26, r 2 = 0.896). The SDA durations showed a slow–fast–slow tendency of decrease with increasing temperature, and were 88.00, 85.71, 67.71, and 66.50 h at 17.5, 22.5, 27.5 and 32.5 °C respectively. Two separate peaks appeared during the SDA response at 17.5 °C, and it might be due to a rapid startup of the mechanical process with a lag of the biochemical process, which suggested that the peaks of “mechanical component” and “biochemical component” of SDA might be separated when temperature was low enough.

Effect of purified macronutrients on specific dynamic action in carnivorous southern catfish

The effect of purified macronutrients on specific dynamic action (SDA) was assessed in juvenile southern catfish (39.81 ± 1.35 g) at 27.5 � C by stuffing iso-energetic (5 kJ) casein, corn oil, corn starch in sections of grass carp intestine (0.25 g). A control (without filler) and mixed diets were also made (each macronutrient provide one-third energy). The postprandial metabolic response, i.e. the oxygen consumption curve, was markedly different among fish fed different food. The peak postprandial metabolic rate of fish fed mixed diet (76.72 mgO2 h )1 ) was significantly higher than that of protein group (66.08 mgO2 h )1 ), while the latter was significantly higher than those of other groups (56.11 mgO2 h )1 for lipid, 54.00 mgO2 h )1 for carbohydrate and 56.09 mgO2 h )1 for control) (P < 0.05). The SDA durations were 32, 32, 30, 14 and 10 h for mixed, casein, corn oil, corn starch and control groups, respectively. The SDA coefficient (energy expended on SDA as per cent of ingested energy) of casein (9.41% 2 ) was significantly higher than that of mixed diet (7.43%) (P < 0.05), while the latter was significantly higher than those of corn oil (3.97%) and corn starch (0.84%) (P < 0.05). The results of this study suggested that the method of using casing on investigation of SDA in carnivorous fish was feasible. The SDA response of carnivorous southern catfish fed protein was higher than lipid while latter was higher than carbohydrate (nearly to zero). The result of this study may give interesting information for understanding the physiological mechanism under SDA.

The energetic consequence of specific dynamic action in southern bluefin tunaThunnus maccoyii

The effect of feeding on the rate of oxygen consumption (M(O2)) of four groups of three southern bluefin tuna Thunnus maccoyii (SBT) was examined in a large static respirometer at water temperatures of 18.2-20.3 degrees C. Six feeding events of rations between 2.1-8.5% body mass (%M(b)) of Australian sardines (Sardinops neopilchardus) were recorded (two of the groups were fed twice). Before feeding, fish swam between 0.71 and 1.4 body lengths s(-1) (BL s(-1)) and the routine metabolic rate (RMR) was 366+/-32.5 mg kg(-1) h(-1) (mean +/- s.e.m.). For all trials, M(O2) was elevated post feeding, presumably as a result of specific dynamic action (SDA). Swimming velocity was also elevated post feeding for periods similar to that of M(O2) (between 20-45 h, longest for the largest rations). Post feeding swimming velocity increased to between 0.87-2.6 BL s(-1) and was also dependent on ration consumed. It is suggested that the purpose of increased post-feeding swimming velocity was to increase ventilation volume as a response to the enhanced metabolic demand associated with SDA. Peak post-prandial M(O2) increased linearly with ration size to a maximum of 1290 mg kg(-1) h(-1), corresponding to 2.8 times the RMR. When converted to its energy equivalent, total magnitude of SDA was linearly correlated with ration size to a maximum of 192 kJ kg(-1) h(-1), and as a proportion of gross energy ingested (SDA coefficient), it averaged 35+/-2.2%. These results demonstrate that, although the factorial increase of SDA in SBT is similar to that of other fish species, the absolute energetic cost of SDA is much higher. These results support the contention that tuna are energy speculators, gambling high rates of energy expenditure for potentially higher rates of energy returns. The ration that southern bluefin tuna require to equal the combined metabolic costs of SDA and RMR is estimated in this study to be 3.5%M(b) of Australian sardines per day.