Effects of meal size, clutch, and metabolism on the energy efficiencies of juvenile Burmese pythons, Python molurus.

We explored meal size and clutch (i.e., genetic) effects on the relative proportion of ingested energy that is absorbed by the gut (apparent digestive efficiency), becomes available for metabolism and growth (apparent assimilation efficiency), and is used for growth (production efficiency) for juvenile Burmese pythons (Python molurus). Sibling pythons were fed rodent meals equaling 15%, 25%, and 35% of their body mass and individuals from five different clutches were fed rodent meals equaling 25% of their body mass. For each of 11-12 consecutive feeding trials, python body mass was recorded and feces and urate of each snake was collected, dried, and weighed. Energy contents of meals (mice and rats), feces, urate, and pythons were determined using bomb calorimetry. For siblings fed three different meal sizes, growth rate increased with larger meals, but there was no significant variation among the meal sizes for any of the calculated energy efficiencies. Among the three meal sizes, apparent digestive efficiency, apparent assimilation efficiency, and production efficiency averaged 91.0%, 84.7%, and 40.7%, respectively. In contrast, each of these energy efficiencies varied significantly among the five different clutches. Among these clutches production efficiency was negatively correlated with standard metabolic rate (SMR). Clutches containing individuals with low SMR were therefore able to allocate more of ingested energy into growth.     

The influence of circadian rhythms on pre- and post-prandial metabolism in the snake Lamprophis fuliginosus

Measuring standard metabolic rate (SMR) and specific dynamic action (SDA) has yielded insight into patterns of energy expenditure in snakes, but less emphasis has been placed on identifying metabolic variation and associated energy cost of circadian rhythms. To estimate SMR, SDA, and identify metabolic variation associated with circadian cycles in nocturnally active African house snakes (Lamprophis fuliginosus), we measured oxygen consumption rates (VO2) at frequent intervals before and during digestion of meals equaling 10%, 20% and 30% of their body mass. Circadian rhythms in metabolism were perceptible in the VO2 data during fasting and after the initial stages of digestion. We estimated SMR of L. fuliginosus (mean mass=16.7+/-0.3 g) to be 0.68+/-0.02 (+/-SEM) mL O2/h at 25 degrees C. Twenty-four hours after eating, VO2 peaked at 3.2-5.3 times SMR. During digestion of meals equaling 10-30% of their body mass, the volume of oxygen consumed ranged from 109 to 119 mL O2 for SMR, whereas extra oxygen consumed for digestion and assimilation ranged from 68 to 256 mL O2 (equivalent to 14.5-17.0% of ingested energy). The oxygen consumed due to the rise in metabolism during the active phase of the daily cycle ranged from 55 to 66 mL O2 during digestion. Peak VO2, digestive scope, and SDA increased with increasing meal size. Comparisons of our estimates to estimates derived from methods used in previous investigations resulted in wide variance of metabolic variables (up to 39%), likely due to the influence of circadian rhythms and activity on the selection of baseline metabolism. We suggest frequent VO2 measurements over multiple days, coupled with mathematical methods that reduce the influence of undesired sources of VO2 variation (e.g., activity, circadian cycles) are needed to reliably assess SMR and SDA in animals exhibiting strong circadian cycles.     

The effect of temperature on digestive and assimilation efficiency,gut passage time and appetite in an ambush foraging lizard,<Emphasis Type="Italic"> Cordylus melanotus melanotus</Emphasis>

In ectotherms, an increase in body temperature increases metabolic rate and may increase rates of digestive processes. We measured the thermal dependence of the apparent digestive and apparent assimilation efficiencies (ADE and AAE), gut passage time (GP) and appetite in Cordylus melanotus melanotus, a medium sized Crag Lizard, which is endemic to South Africa. Trials were conducted at 20, 22, 25, 30, 32 and 35 °C under controlled conditions. Trials lasted 14 days, during which, lizards were fed ca. 1 g mealworms per day. Glass beads were used as markers to determine GP at the beginning and end of trials. Faeces and urates were collected daily and oven dried at 50 °C. The energy content of egested matter was then measured using bomb calorimetry. ADE and AAE were not affected by temperature for either males or females. The mean±SE ADE and AAE were 94.4±0.3% and 87.2±0.6%, respectively. GP was not significantly different between males and females at any temperature, but decreased significantly with increasing temperature. Appetite was significantly different between the different temperatures measured. The decrease of gut passage time with increasing temperature was expected, since the digestive and assimilation efficiencies are similar over the range of temperatures tested. Lizards are thus assimilating a similar proportion of ingested energy, but at faster rates at higher temperatures. The results indicate that the digestive physiology of this species results in maximum energy gain per meal in environments where food is scarce.Abbreviations AAE apparent assimilation efficiency - ADE apparent digestive efficiency - AE assimilation efficiency - DE digestive efficiency - GP gut passage rate - NEA net energy absorbed through gut - NER net usable energy retained - SVL snout-vent length - T _b body temperature Communicated by G. Heldmaier     

Digestive efficiency of a generalist avian feeder,the Cape White-eye (Zosterops pallidus)

Digestive processes determine whether the particular diet of a bird is utilized efficiently and whether energetic demands are met. Assimilation efficiency is often used as an index of whether a diet is digested optimally. Studies on the digestive processing of generalist feeders are scarce. Cape White-eyes (Zosterops pallidus) have a diverse diet of fruit, nectar and insects. The nutrient contents of these three diets vary considerably and require quite different digestive processing. This study compared the digestive efficiencies of Cape White-eyes on these three diets by measuring transit times and assimilation efficiency. Cape White-eyes lost body mass significantly when fed fruit, while they maintained and gained body mass on nectar and mealworm diets, respectively. Assimilation efficiency varied significantly between the three diet types (nectar>mealworms>apples). When given a choice of diets, Cape White-eyes selected the diet, which was most efficiently digested and yielded the greatest energetic reward. Diet preference trials further showed that Cape White-eyes regulated daily energy intake. Assimilation efficiency depends on the accessibility of nutritional contents of a diet. Cape White-eyes did not maximize assimilation efficiency. Instead, they adjusted transit time to maximize the rate of energy gain per gram of food in order to maintain energy balance.     

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 effects of fasting duration on the metabolic response to feeding in Python molurus: an evaluation of the energetic costs associated with gastrointestinal growth and upregulation

The oxygen uptake of Python molurus increases enormously following feeding, and the elevated metabolism coincides with rapid growth of the gastrointestinal organs. There are opposing views regarding the energetic costs of the gastrointestinal hypertrophy, and this study concerns the metabolic response to feeding after fasting periods of different duration. Since mass and function of the gastrointestinal organs remain elevated for several days after feeding, the metabolic increment following a second meal given soon after the first can reveal whether the metabolic costs relate to the upregulation of gastrointestinal organs or merely the metabolic cost of processing a meal. Eight juvenile pythons were kept on a regular feeding regime for 6 mo after hatching. At the beginning of the metabolic measurements, they were fed mice (20% of body mass), and the metabolic response to similarly sized meals was determined following 3, 5, 7, 14, 21, 30, and 60 d of fasting. Our data show that the metabolic response following feeding was large, ranging from 21% to 35% of ingested energy (mean=27%), but the metabolic response seems independent of fasting duration. Hence, the extraordinarily large cost of digestion in P. molurus does not appear to correlate with increased function and growth of gastrointestinal organs but must be associated with other physiological processes.     

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.     

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 W^1.04 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 W^0.976 The 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.     

Utilization of copra meal in the formulation of compound diets for rohu, Labeo rohita, fingerlings

Six isonitrogenous (35% crude protein) experimental diets were formulated with raw and soaked de-oiled copra meal substituted for fish meal in the diet at 20, 30 and 40% levels by weight. The tannin content of raw de-oiled copra meal was reduced from 2.4 to 0.9% by soaking it in water for 16 h at room temperature. The response of rohu, Labeo rohita (Hamilton), fingerlings fed these diets for 80 days was compared with fish fed a fish meal-based control diet. On the basis of growth response, food conversion ratio and protein efficiency ratio, the 30% soaked copra meal diet resulted in the best fish performance (P < 0.01). The growth response of the fish was significantly (P < 0.01) affected by both type and inclusion level of the oilseed meal. The growth of fish declined with the increasing level of inclusion of copra meal, irrespective of the type of meal used. The apparent protein digestibilities (APDs) for the raw copra meal were lower at all levels of inclusion in comparison with those for the soaked meals. The highest amount of carcass protein was recorded in the fish fed the diet containing 30% soaked copra meal. The results showed that de-oiled copra meal can be incorporated into carp diets up to 20% in the raw condition and up to 30% in the treated condition without any deleterious effects on growth performance of Labeo rohita fingerlings.     

Individual variations and interrelationships in feeding rate,growth rate,and spontaneous activity in hybrid tilapia (Oreochromis niloticus × O. aureus) at different feeding frequencies

A 30‐day growth trial was conducted to investigate the individual variations in feeding rate, growth rate, spontaneous activity, and their possible interrelationships in hybrid tilapia (Oreochromis niloticus × O. aureus) reared individually at feeding frequencies of one and two meals daily. Results show that the feeding rate in energy (FRe), specific growth rate in energy (SGRe), and food conversion efficiency (FCE) of fish fed twice a day were significantly higher than that of fish fed only once. However, no significant differences in distance or in time spent swimming were observed between the groups. SGRe was positively correlated with FRe in fish fed only once daily, and SGRe was positively correlated with food conversion efficiency in energy (FCEe) between the two groups. SGRe was only inversely correlated with the distance that fish swam when fed once daily. The results suggest that the individual growth differences of hybrid tilapia could be attributed mainly to variations in FRe, and that the energy costs of spontaneous activity play an important role in the differences at feeding frequency of one meal a day. However, at feeding frequencies of two meals a day, individual growth differences in fish may be caused by variations in FCEe, and energy costs of spontaneous activity have only marginal effects on the differences.     

Effects of dietary soybean protein levels on energy budget of the southern catfish, Silurus meridionalis

Energy budgets were calculated for the southern catfish, Silurus meridionalis, fed diets replacing 0%, 13%, 26%, 39%, 52% and 65% fish meal protein with soybean meal (SBM) protein with or without methionine supplementation to apparent satiation at 27.5 °C. With increasing dietary soybean protein levels (SPL), the feed energy lost in feces, excretion and metabolism increased, while that available for growth decreased (P < 0.05). When 0.12% or 0.26% methionine at 39% SPL was added to reach that in body carcass or the control group (0% SPL), no significant differences were found in each component of energy budgets. When 0.21% or 0.33% methionine at 52% SPL was added to reach the content of methionine in body carcass or the control group, energy spent on growth increased, but that on excretion and metabolism decreased (P < 0.05). These results suggested that the differences in growth rate among the southern catfish fed the diets with different SPL were due to decreasing absorption rate, increasing excretion and metabolism with increasing dietary SPL. The most important factor limiting the use of soybean protein was the imbalance of essential amino acids, which resulted in more energy spent on metabolism and excretion, less energy on growth. Supplementation of methionine produced a relatively better amino acid profile and subsequently improved the utilization of soybean protein at high SPL, which resulted in less energy used for metabolism or lost in excretion and more energy available for growth.     

Ingestion,Digestion and Assimilation Efficiency of the Sea-Anemone Aiptasia pallida Fed Zooplankton Prey

Ingestion time, digestion time, and assimilation efficiency by the sea anemone Aiptasia pallida were studied in the laboratory by feeding individual anemones preweighed pellets of freeze-dried Artemia salina nauplii. There was no significant correlation between anemone size, measured as dry weight, and either ingestion time, digestion time or assimilation efficiency. Similarly, there was no significant correlation between meal size (i.e., dry weight of ingested brine shrimp pellet) and either ingestion time, digestion time or assimilation efficiency. These results suggest that, under these conditions, assimilation efficiency is unaffected by either “meal” size or anemone size.     

Temperature and meal size effects on the postprandial metabolism and energetics in a boid snake

We investigated the combined effect of meal size and temperature on the aerobic metabolism and energetics of digestion in Boa constrictor amarali. Oxygen uptake rates (Vd2;o2) and the duration of the digestion were determined in snakes fed with meals equaling to 5%, 10%, 20%, and 40% of the snake's body mass at 25 degrees and 30 degrees C. The maximum Vd2;o2 values attained during digestion were greater at 30 degrees C than at 25 degrees C. Both maximal Vd2;o2 values and the duration of the specific dynamic action (SDA) were attained sooner at 30 degrees C than at 25 degrees C. Therefore, the temperature effect on digestion in Boa is characterized by the shortening of the SDA duration at the expense of increased Vd2;o2. Energy allocated to SDA was not affected by meal size but was greater at 25 degrees C compared to 30 degrees C. This indicates that a postprandial thermophilic response can be advantageous not only by decreasing the duration of digestion but also by improving digestive efficiency. Maximal Vd2;o2 and SDA duration increased with meal size at both temperatures.     

Comparison of digestive efficiency in the parasitic great spotted cuckoo and its magpie host nestlings

Altricial nestlings are under strong selection pressures to optimize digestive efficiency because this is one of the main factors affecting nestling growth and survival. Bird species vary in their ability to assimilate different nutrients and current theory predicts that nestlings should also be able to adjust their nutritional physiology to feeding frequency. Variation in parental provisioning to nestlings would select for flexibility in nestling digestive physiology, which would allow maximization of nutrient assimilation. In the present study, by making use of a brood parasite–host study system in which great spotted cuckoo nestlings (Clamator glandarius) are reared by magpie (Pica pica) host foster parents when sharing the nest with host nestlings, we tested several predictions of the adaptive digestive efficiency paradigm. A hand‐feeding experiment was employed in which we fed both great spotted cuckoo and magpie nestlings with exactly the same diet simulating one food abundance period and one food deprivation period. The results obtained show that cuckoo nestlings ingested more food, gained significantly more weight during the abundance period, and assimilated a higher proportion of the ingested food than magpie nestlings. These results demonstrate for the first time that cuckoo nestlings enjoy digestive adaptations that favour a rapid processing of the ingested food, thereby maximizing their intake rate but without decreasing digestive efficiency. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 280–289.     

Nutritional evaluation of fermented black gram (Phaseolus mungo) seed meal in compound diets for rohu, Labeo rohita (Hamilton), fingerlings

Six isonitrogenous (approximately 35% crude protein) and isocaloric (approximately 4.0 kcal g⁻¹) diets were formulated incorporating raw and fermented black gram, Phaseolus mungo, seed meal at 20%, 30% and 40% levels by weight into a fishmeal‐based control diet fed to rohu, Labeo rohita, fingerlings (mean weight, 1.81 ± 0.21 g) for 80 days for a study of fish performance. A particular bacterial strain (Bacillus sp.) isolated from the intestine of adult common carp (Cyprinus carpio) reared in the wild having significant amylolytic, cellulolytic, lipolytic and proteolytic activities was used for fermentation of seed meal for 15 days at 37 ± 2°C. Fermentation of P. mungo seed meal was effective in significantly reducing the crude fibre content and antinutritional factors such as tannins and phytic acid, and enhancing available free amino acids and fatty acids. In terms of growth, feed conversion ratio and protein efficiency ratio, the 30% fermented black gram seed meal incorporated diet resulted in a significantly (P < 0.05) better performance of rohu fingerlings. In general, growth and feed utilization efficiencies of diets containing fermented seed meal were superior to diets containing raw seed meal. The apparent protein digestibility (APD) values decreased with increasing levels of raw seed meal in the diets. The APD for raw seed meal was lower at all levels of inclusion in comparison to those for the fermented seed meals. The maximum deposition of protein in the carcass was recorded in fish fed the diet containing 40% fermented seed meal. The results indicate that fermented black gram seed meal can be incorporated in carp diets up to the 30% level compared to the 10% level of raw seed meal.     

Use of soybean flour (dehulled, solvent-extracted soybean) as a fish meal substitute in practical diets for African catfish, Clarias gariepinus (Burchell 1822): growth, feed utilization and digestibility

Growth and digestibility trials were conducted using African catfish, Clarias gariepinus (Burchell 1822): (1) to obtain apparent digestibility coefficient (ADC) values for capelin fish meal, soybean flour and corn meal; (2) to formulate diets based on ADC values of the protein feedstuffs; and (3) to evaluate the effects of replacing 25%, 50% and 75% of fish meal in control diets with soybean flour on growth, feed utilization efficiency and carcass composition. Supplemental methionine was added to the diet formulation in which soybean flour replaced 75% of the diet. Diets were formulated (400 g digestible protein kg⁻¹ and 15 kJ digestible energy g⁻¹ dry diet) and fed to catfish fingerlings (13.1 ± 0.5 g) to apparent satiation twice daily for 70 days. The protein and energy digestibilities of fish meal and soybean flour were high (>90% and >80%, respectively; P < 0.05). At 75% fish meal replacement with soybean flour (without methionine supplementation), growth and feed utilization efficiency indicators were depressed compared with other diet treatments which had a similar (P > 0.05) growth and feed utilization efficiency to those fed the control diet. The carcass compositions of catfish in all diets were similar (P > 0.05) and the liver histology of catfish fed any of the diets showed no alterations. The results obtained indicate that 50% of fish meal protein in practical catfish diets can be replaced with soybean flour and that catfish can effectively utilize supplemental methionine, thereby allowing up to 75% of the dietary fish meal protein to be replaced by soybean flour.     

Effect of water temperature,feeding frequency,and protein percent in the diet on water quality,growth and behavior of Nile tilapia Oreochromis niloticus (Linnaeus, 1758)

This study evaluated how water temperature (26, 28, and 30°C), number of meals per day (one or two meals), and protein percent in diet (20, 25 and 30%) impact growth performance, biometric indices, and feeding behavior of Nile tilapia, Oreochromis niloticus. Fish were randomly allocated into 18 equal replicate groups. Higher final body weight was observed in fish reared at 30°C and fed one meal per day containing 30% crude protein. Better weight gain, weight gain %, feed conversion ratio, specific growth rate, and condition factor were recorded in fish reared at 26°C and fed one meal per day containing 30% protein. The best length weight relationship was obtained in fish reared at 26°C and fed one meal per day containing 30% crude protein. Shorter feeding duration and duration of appetite inhibition latency were recorded in fish reared at 30°C, fed one meal per day, and given a diet containing 30% protein. The highest proactivity was recorded in fish reared at 30°C, received one meal per day, and with 25% crude protein in their diet. Conclusively, rearing Nile tilapia at 26–30°C with a lower feeding frequency (one meal/day) and a 30% crude protein diet achieved better performance and feeding behavior.     

The effects of ration level on food retention time in juvenile lemon sharks,Negaprion brevirostris

Synopsis Fecal production was monitored to observe the effects of meal size on retention time of food in the digestive tracts of lemon sharks, Negaprion brevirostris. Initial appearance of feces occurred more rapidly when ration level was increased. The onset of fecal production was negatively correlated with rate of intake. Production of feces continued for a longer period of time when meal size was increased. Retention time of food was directly related to feeding rate, suggesting that the rate of digestion was constant. The correlation between retention time and intake on a percentage body weight basis was greater than the correlation between retention time and intake on an energy density basis. The use of agar to bind food may have delayed digestion and prolonged food passage for sharks fed an experimental diet.     

The inhibitory effects of the molluscicide metaldehyde on feeding, locomotion and faecal elimination of three pest species of terrestrial slug

Single meals on maize flour pellets containing 0, 0·5, 1, 2, 4, 6, and 8% metaldehyde were analysed in Arion hortensis (agg), Deroceras reticulatum and Deroceras caruanae, by attaching the pellets to a mechanical transducer from which signals were ultimately fed into a BBC microcomputer for on-line analysis. Post-feeding tests were used to investigate toxic effects of metaldehyde and the recovery of slugs was examined daily for 7 days. Bite rates were slightly lower and more irregular on metaldehyde meals especially in A. hortensis. The meal length and number of bites per meal were markedly inhibited by metaldehyde and inversely proportional to the concentration. The size of the bites was also reduced, by about 30%, in meals on 6% pellets compared with 0%. Clear symptoms of poisoning became evident during the meal or normally in the 16-min test period immediately afterwards. In these tests slugs which fed on metaldehyde pellets showed a disruption of their ability to right themselves (after being placed on their side), less activity and a reduced probability of accepting a ‘dummy’ pellet containing no metaldehyde. It is hypothesised that feeding is prematurely terminated primarily because of the toxic effects of the metaldehyde and that aversion also acts to terminate the meal early, by decreasing the probability of continuing to feed as the meal proceeds. At higher concentrations of metaldehyde aversion may be more important than the toxic effects in ending the meal. Faecal elimination is delayed after metaldehyde meals and this contributes to mortality. The estimated lethal doses were about 0·2 mg/g body weight of slug in Deroceras spp. A. hortensis was less susceptible. To increase the likelihood of a lethal dose being ingested the inhibition of feeding needs to be overcome, at least partly, and the results presented indicate the need for a bait formulation which reduces the rate of absorption of the molluscicide from the gut.     

Change of cardiac function, but not form, in postprandial pythons

Pythons are renowned for a rapid and pronounced postprandial growth of the heart that coincides with a several-fold elevation of cardiac output that lasts for several days. Here we investigate whether ventricular morphology is affected by digestive state in two species of pythons (Python regius and Python molurus) and we determine the cardiac right-to-left shunt during the postprandial period in P. regius. Both species experienced several-fold increases in metabolism and mass of the digestive organs by 24 and 48 h after ingestion of meals equivalent to 25% of body mass. Surprisingly there were no changes in ventricular mass or dimensions as we used a meal size and husbandry conditions similar to studies finding rapid and significant growth. Based on these data and literature we therefore suggest that postprandial cardiac growth should be regarded as a facultative rather than obligatory component of the renowned postprandial response. The cardiac right-to-left shunt, calculated on the basis of oxygen concentrations in the left and right atria and the dorsal aorta, was negligible in fasting P. regius, but increased to 10-15% during digestion. Such shunt levels are very low compared to other reptiles and does not support a recent proposal that shunts may facilitate digestion in reptiles.