Gut evacuation and absorption efficiency of walleye larvae

Gut evacuation and absorption efficiency in zooplanktivorous walleye Stizostedion vitreum larvae (10–19 mm; 0.53–6.8 mg dry weight) were examined in the laboratory. The decline in dry weight of whole digestive tract contents was examined at 15, 20, and 25) C in discontinuous feeding larvae. The observed relationship between short-term evacuation rate and gut fullness indicated that evacuation approximated most closely an exponential decline. When gut evacuation rate, R , was calculated as the slope of loge gut fullness v . time there were significant effects of temperature and walleye size on R . Gut evacuation rate was higher at 20° C than at 15 or 25° C and declined with increasing walleye dry weight. Absorption efficiency at 20° C was examined by qualitative analysis of food and faeces. Apparent digestibility, D _a, of crustacean zooplankton increased with gut retention time and declined with walleye dry weight. Maximum D _a was estimated to be 79% of organic matter from food retained in the gut for 6 h.     

A bacteriological investigation to elucidate the feeding biology of Nais variabilis (Oligochaeta: Naididae)

SUMMARY. The estimated average number of bacteria in the gut of laboratory-cultured Nais variabilis was 100.4 × 10⁴. This compares with values of 6.7 × 10⁴ and 32.8 × 10⁴, respectively, for N. variabilis and N. barbata obtained from a river.
Comparison of the viability of heterotrophic bacteria in the food and gut of N. variabilis indicated a decline in viability of up to 99.6% during the passage of bacteria through the gut. The estimated gut retention time was 39 ± 8 min at 18°C and therefore loss of viability is unlikely to be due to long retention in the gut. Loss of viability is, however, a prerequisite of bacterial digestion by the worm and provides circumstantial evidence that ingested bacteria are used as food.
No conclusive evidence was obtained indicating (a) preferential ingestion of certain kinds of bacteria, (b) that the gut environment was selectively hostile to the particular kinds of bacteria studied or (c) that worms had a specialized gut micro-flora.     

An in situ estimate of daily food consumption and alimentary canal evacuation rates of common carp, Cyprinus carpio L.

Daily food consumption and alimentary canal evacuation rates for common carp, Cyprinus carpio L., were estimated at 4-week intervals from April to October 1979. Both the rate of food evacuation and its relationship to temperature were described by an exponential function. Gut evacuation rates ranged from 6.0% of gut contents per hour at 9°C to 32.7% h⁻¹ at 26.5°C. Temperature accounted for 72–91% of the variation in gut evacuation rate among months. Daily food consumption varied from a low of 3.87 mg g⁻¹ of fish wet wt per day in April at 14°C (0.39% of wet body wt) to a high of 40.75 mg g⁻¹ (4.08%) in August at 26.5°C. Although a greater quantity of food appeared to be consumed during the morning in spring and early summer and a greater amount in the evening after July, there was not a statistically significant time of day for peak feeding activity. The field method described here seemed to provide reasonable estimates of food consumption compared with other field and laboratory studies.     

Seasonal change in the gastric evacuation rate of rainbow trout feeding on natural prey

Seasonal changes in the gastric evacuation rate ( R ) and gut contents of a wild population of rainbow trout Oncorhynchus mykiss feeding on natural prey at four water temperatures (2, 7, 9 and 12° C) were measured. The R and mass of the gut contents increased with water temperature, and prey items changed seasonally. These results suggest that the R of fish feeding on natural food depends primarily on water temperature, with their consumed prey being a secondary factor.     

Regulation of digestive proteolytic activity in the larvae of Spilosoma obliqua (Lep., Arctiidae)

Proteolytic activity from the guts of the lepidopteran larvae Spilosoma obliqua was studied in relation to the developmental stages. The activity was found to increase with the advancement in the age of larvae and decreased with the onset of pupation. Starvation of fifth instar larvae, which exhibited maximum proteolytic activity, led to an increase at 8 h and declined further. There seems to be a possible relationship between the availability of the food and secretion of the enzymatic activity. The optimum pH and temperature for the gut protease was 11.0 and 50°C, respectively. Incubation of the gut protease for 24 h at 37°C led to a decrease in 52% of the activity, whereas there was a decrease of 17% in the activity at 4°C. No evidence could be found for the existence of the protease as an inactive precursor. The alkaline properties of the digestive protease seem to have all the potential to be exploited commercially as a additive in various biological formulations.     

Gut evacuation of walleye pollock larvae in response to feeding conditions

Gut residence times of first-feeding walleye pollock larvae were measured at 6°C in continuous and discontinuous feeding regimes. Larvae fed tagged copepod prey evacuated their guts more quickly in continuous feeding as compared to the discontinuous feeding treatment. The mean gut residence time was estimated to be 5.0 h for larvae feeding continuously. Gut evacuation by larvae fed tagged prey and then isolated without food (discontinuous treatment) was slower and more variable, with an estimated gut residence time exceeding 8.0 h. Field and laboratory observations suggest that the larval fish gut may be modeled as an intermittent plug-flow reactor (PFR) in response to diel feeding patterns. The cyclical nature of gut dynamics has implications for gut content analyses and the estimation of daily food rations.     

Aspects of the symbiosis of the leaf-cutting ant Acromyrmex octospinosus (Reich) and its food fungus

Abstract. 1. Laboratory ants preferred eating whole ant fungus staphylae to hyphae, and did not feed on other fungi. Homogenized ant fungus staphylae and hyphae were equally acceptable liquid food but other homogenized fungi were not drunk extensively.
2. Various arthropod fungjvores preferred to feed on ant fungus rather than any other fungus tested. Some preferred hyphae to staphylae, some vice versa and others had no preference.
3. The ants attacked animals on the nest and reduced the numbers of fungivores on the fungus garden.
4. The ant fungus grew best at 24.5°C and hardly at all at 10°C or 37°C.
5. The ants did not necessarily choose material which supported the best fungus growth in sterile culture and readily accepted substrates on which the fungus did not grow at all. No learning behaviour was noted.
6. The ant X fungus symbiosis is discussed as an example of co-evolution, a product of an evolutionary feedback. The ant is supplied with a highly nutritious, readily acceptable food source in return for complex fungus-culture behaviour, providing protection from fungivores and competition from other saprophytic fungi.     

Coprophagy: a supplementary food source for two freshwater gastropods?

1. The freshwater pulmonate snail Radix peregra voluntarily and regularly fed on its faeces, whereas Bithynia tentaculata (Prosobranchia) did not.
2. With high-quality faeces as food (faeces with C : N-values below ten) Radix could grow and survived for 11 weeks. Growth was 24–30% of that achieved with control food (lettuce, Chlamydomonas and Tetramin), and body mass was close to the expected value.
3. As with real food, the percentage organic content of faeces was reduced during gut passage, with the exception of very low-quality faeces.
4. Faeces contained living cells of green algae ( Chlamydomonas reinhardii ) and diatoms ( Achnanthes lanceolata, Eunotia pectinalis ), which survived the gut passage of R. peregra and B. tentaculata . Faecal material was also rich in bacteria, with up to 150 × 10⁶ cells mg^–1 dry mass. Bacteria increased in abundance in faeces which had been evacuated for 7 days or more.
5. A further degradation of partly digested food in the faeces was indicated by the activity of the extracellular digestive enzymes cellobiase and chitobiase. These enzymes hydrolysed material with an activity of 0.2–14.5 pkat mg^–1 faecal dry mass in 1–12-day-old faeces. In faeces of Bithynia fed control food or incubated sycamore leaves, chitobiase activity was correlated with bacterial abundance.
6. Coprophagy is considered to be a suitable strategy for further degradation and utilization of refractory material for which one gut passage is too short and/or too inefficient.     

The enumeration of thermotrophic types amongst the Enterobacteriaceae colonizing perishable foods

A total of 41 pure cultures of Enterobacteriaceae, comprising 32 thermotrophic and nine psychrotrophic strains, pathogens or marker organisms, were examined for numbers of colony forming units obtained at 37° and 42°5°C (thermotrophs) and 30°C (psychrotrophs), when surface-plated on a rich infusion agar and violet red bile agar. In addition 42 food and water samples, collected in a rural area of the Philippines, were examined by surface inoculating violet red bile AIPC (agar immersion plating and contact; 'dip') slides and incubating at 37° and 42°5°C. At 42°5°C there was almost total recovery of the thermotrophic Enterobacteriaceae, whereas the psychrotrophic strains were completely suppressed. At 37°C the psychrotrophs were only slightly inhibited. The Philippine foods, predominantly cooked meals, milk and drinking water, appeared to be significantly colonized by thermotrophic Enterobacteriaceae. It is concluded that incubation at 42°5°C satisfactorily selects enteropathogenic and other enteric Enterobacteriaceae while suppressing the psychrotrophic types which are mainly of vegetable origin. It is emphasized that, regardless of the temperature used, a resuscitation procedure for Enterobacteriaceae populations that have incurred sublethal injury in food has to precede counts on or in the usual selective media.     

The Development and Survival of the Blood-Stream Forms of Trypanosoma conorhini in Culture

SYNOPSIS. Trypanosoma conorhini has been isolated from infected Triatoma rubrofasciata in Singapore. Parasites derived from the triatomid gut were inoculated into NNN medium and some cultures maintained at 25° to 27°C while others were kept at 37°. In cultures kept at lower temperatures crithidial forms predominated; however, at 37° blood-stream trypanosome forms developed and survived for 10 days or more.     

Early development of the digestive tract of cod larvae, Gadus morhua L., during start-feeding and starvation

Cod larvae, Gadus morhua L., were reared in the laboratory and released to a large marine enclosure 4 to 5 days after hatching (6–8° C). The development of the digestive system was studied until day 24 after hatching. Morphological investigations of the jaw apparatus and the digestive tract showed that the larvae are able to absorb ingested food well before exhaustion of the yolk sac. The foregut, and especially the midgut, were particularly active in lipid absorption, and the hindgut was characterized by pinocytotic activity. Duhng the first days of feeding, no distinct prey organisms were observed in the gut, and signs of food absorption in the epithelial cells of the gut were sparse.A distinct red fluorescence, restricted to the hindgut, was observed from day 11 to day 19. On the basis of changes in absorptive pattern in the gut we suggest that changes in digestive and absorptive abilities, as well as in nutritional needs, take place around days 15–17 after hatching.
In starved larvae, signs of degeneration of the gut tissue were first visible in the foregut. By day 9 after hatching, microvilli was degenerated to such an extent that the ability to absorb food must have been severely restricted. If larvae are starved longer than this, they will probably not survive.     

Food web of macroinvertebrate community in a Yangtze shallow lake: trophic basis and pathways

No detailed food web research on macroinvertebrate community of lacustrine ecosystem was reported in China. The present study is the first attempt on the subject in Lake Biandantang, a macrophytic lake in Hubei Province. Food webs of the macroinvertebrate community were compiled bimonthly from March, 2002 to March, 2003. Dietary information was obtained from gut analysis. Linkage strength was quantified by combining estimates of energy flow (secondary production) with data of gut analysis. The macroinvertebrate community of Lake Biandantang was based heavily on detritus. Quantitative food webs showed the total ingestion ranged from 6930 to 36,340 mg dry mass m⁻² bimonthly. The ingestion of macroinvertebrate community was higher in the months with optimum temperature than that in other periods with higher or lower temperature. Through comparison, many patterns in benthic food web of Lake Biandantang are consistent with other detritus-based webs, such as stream webs, but different greatly from those based on autochthonous primary production (e.g. pelagic systems). It suggests that the trophic basis of the web is essential in shaping food web structure. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Consumption of food and spatial organization of digestion in the cassava hornworm, Erinnyis ello

Fifth-instar Erinnyis ello larvae eat 2.1 times their own weight per day of Euphorbia pulcherrima leaves, with a coefficient of digestibility of 45% and an efficiency of food conversion into tissue of 25%. The food takes about 150 min to go through the gut. Midgut contents have a pH of 9.3–9.8, depending on the region. Cellulase is absent from the gut in E. ello. Significant gut hydrolase activities are found only in midgut. Amylase and trypsin occur in the midgut tissue and contents and in regurgitated material, whereas aminopeptidase, α-glucosidase, β-glucosidase and trehalase are found in major amounts in the midgut tissue, in minor amounts in the midgut contents and are absent from regurgitated material. The results support the hypothesis that digestion starts in the endoperitrophic space under the action of amylase and trypsin and is largely completed in the ectoperitrophic space through the catalytic action of several oligomer and dimer hydrolases. Involvement of a membrane-bound aminopeptidase in the terminal digestion of oligopeptides cannot, at present, be excluded. The finding that less than 7% of the total amylase and trypsin are excreted, after a time identical to the passage time of the food bolus, leads to the proposal for the existence of some mechanism by which those enzymes are recovered from the undigested food before it is excreted.     

Digestive processes during the development of the roach, Rutilus rutilus L.

During development of the roach from larvae to adults relative gut length increases from 44 to 104% of the body length. Gut passage rate correlates with gut length, ranging from 2.25 h in larvae to 6.2 h in adults (at 20 ± 1°C). In controlled experiments (20°C, feeding on carp diet) tryptic activity of the gut content increases with the age of the fish. In larvae artificial diet leads to considerable increase of tryptic activity, but to low growth rate and finally to total mortality. The reabsorption of digestive enzymes in the hindgut is efficient only in adults in which tryptic activity in the second half of the intestine is reduced to about 12% of total activity.     

Visual observations on the process of digestion and the production of faecal pellets in the chaetognath Sagitta hispida Conant

The passage of food through the gut of Sagitta hispida Conant is described as a batch process and the formation of membranes which surround the faecal material is demonstrated photographically. The utility of such a peritrophic membrane system is considered in the light of the marine ecosystem as a whole.     

TRANSPORT OF UNCONTAMINATED AND MOLLUSCICIDE-CONTAINING FOOD IN THE DIGESTIVE TRACT OF THE SLUG DEROCERAS RETICULATUM (MULLER)

By X-ray analysis of food transport in the alimentary tractof Deroceras reticulatum it was shown that even ten hours afteringestion of a thorium sulfate-containing bait, this materialcan be detected in the crop. After 2.5 h, some parts of labelledfood passes down from the anterior to the posterior part ofthe gut. After 13 h, thorium sulfate-containing material canbe observed only in the gut. After 19 h, no more labelled materialis present in the alimentary tract of the animals. After addition of Cloethocarb, the animals feed on only smallamounts of food. The labelled material only enters the anteriorpart of the gut. After ten hours, the food does not move anymore and does not leave the crop even 19 h after feeding. After molluscicide application, the crop epithelium is moreinfolded than in control animals and the cells are elongated.After 30 h, cells protrude into the lumen of the digestive tract. (Received 11 May 1992; accepted 26 June 1992)     

Feeding and the control of volume within the tests of regular sea-urchins

The rigid, fluid filled, echinoid test presents problems of internal volume control when the vital functions of the animal involve the introduction of material, from outside the test, into the internal fluid systems. The volume of food in the guts of echinoids can be shown to vary considerably in the short term, to an extent which demands considerable capabilities for internal volume compensation. This is achieved by adjusting the quantity of fluid held within the gut so that, although the volume of food may vary widely, the total volume of the gut remains constant within narrow limits. The volume of gut fluid varies inversely with the quantity of food, and ingestion of food through the mouth is compensated by ejection of an equal volume of fluid from the anus. Defaecation is compensated by intake of fluid into the gut. On starvation, the gut becomes completely fluid filled and free from food.
The food of regular urchins is habitually compacted into regularly sized subpherical pellets covered with a tough mucus coating. The formation of coated pellets takes place in the buccal cavity and pharynx. The pellets remain discrete throughout their passage along the gut. The mucus coating resists digestion and remains intact even after defaecation. The functional morphology of the buccal cavity and pharynx is described in detail.
It is suggested that the functional significance of the pellets is associated with the gut fluid, volume compensation mechanism, which requires free flow of fluid throughout the length of the gut. It is also suggested that the siphon may be implicated in volume control, where fine adjustment of gut volume can be achieved by balancing ejection of fluid from the anus with intake of water through the mouth, but that the water intake is by the siphonal route, thus avoiding the necessity of flushing and diluting the enzyme rich digestive stomach region.     

Supercooling points of insects and mites on the Antarctic Peninsula

Abstract. 1. Mean supercooling points of eleven species of arthropods (three Collembola, seven Acari and one Diptera) ranged from -6.2 to -9.4°C (high group), and from -17.7 to -31.0°C (low group). The majority of individuals in the high group had food in their gut systems.
2. Freezing was lethal to all species examined except larval Belgica antarctica Jacobs (Chironomidae).
3. Glucose, glycerol and mannitol were found in low concentrations in extracts of Ctyptopygus antarcticus Willem (Collembola) and larvae of B. antarcrica; it is udikely that these substances had a major effect on the supercooling of either species.
4. Two Collembola species possessed significantly ( P< 0.05) lower supercooling points at locations on the Antarctic Pensinsula than at Signy Island, South Orkney Islands. The converse was observed for two species of Acari.
5. It is suggested that whilst gross climatic and also micro-habitat conditions may influence the cold hardiness of such arthropods, especially seasonally, their full supercooling ability is rarely tested.     

The food of emus

The results of a study of the food of emus, Dromaius novaehollandiae, in inland Western Australia show that they feed on a great variety of fruits, seeds, flowers, insects and green herbage of annual and perennial plants. Shrubs provide most of the food in spring and autumn (September to March), annuals in the autumn and winter (April to August) and insects are taken whenever they occur in abundance, usually in autumn and spring. Although shrubs provide a reliable supply of food in summer, annuals often produce little in the autumn and winter so that emus would have to move extensively to keep in contact with a supply of food. Records from other parts of Australia indicate that the type of food eaten by emus is similar throughout the continent, but the precise species eaten varies from time to time and place to place. Some incidental observations on characteristics of the digestive system of emus are reported. Large quantities of mineral material are carried in the gizzard and individual items may be retained for 3 or 4 months. The acidity of the anterior sections of the gut make bacterial action unlikely. The crude form of copography has been observed. Some food passes through the gut in 3h but other material from the same intake may be retained for at least 48 h. The emu's diet is nutrient-rich, but only a catholic taste and great mobility ensure that it is able to find a continuous supply of food.