Gut Volume Research Articles

Utilization of autochthonous macroinvertebrate drift by a pool fish community in a woodland stream

Qualitative and quantitative drift data were collected simultaneously above and below a pool both before and after the pool was heavily electrofished. These data revealed no significant difference between drift organism densities (#/m3) above or below the pool before or after fish collection. Qualitative and quantitative fish gut analyses suggest that the sunfishes Lepomis megalotis, L. macrochirus and L. cyanellus may be feeding on drifting invertebrates as these organisms comprised 58%, 37% and 35% gut volume, respectively. A design for a long-term drift net apparatus is presented.

Predicting particle selection by deposit feeders: A model and its implications 1

A feeding model for a generalized, benthic deposit feeder is derived from a filter‐feeding model and used to predict how such a deposit feeder would adjust its feeding to maximize its net energy gain. Under the assumption that deposit feeders are utilizing the bacterial fraction of the sediment or other surface organic coatings as food, the model predicts that the smallest particles should always be ingested, while the selection of larger particles depends on several parameters, including gut passage time and assimilation efficiency of the deposit feeder. The model also predicts relationships among particle size selection, assimilation efficiency, gut passage time, gut volume, and particle rejection costs.

Natural food, foregut clearance-rate and activity of the crab Scylla serrata

The natural diet, rate of foregut clearance and diurnal activity of the crab Scylla serrata were determined. The gut volume is related to size of crab as gut volume (ml)=0.07e0.033x, where x=carapace width in millimetres. Fifty per cent of crabs collected in Australia and South Africa contained molluscan remains and about 21% contained crustacean remains — chiefly grapsid crabs. Fish remains were rarely found, and it was concluded that S. serrata does not normally catch mobile forms such as fish and penaeid prawns. Gut clearance of organic tissue was rapid and almost complete after 12 h. Fish bone was retained for a mean time of 2 to 3 days, and shell for 5 to 6 days. Time-lapse photography, using infra-red light, was used to record activity. Visible light flashes reduced activity. S. serrata remained buried during the day, emerging at sunset to spend the night feeding, which occurred intermittently even when unlimited food was available. If no food was present the amount of time spent on the substrate surface was halved.

Spinal and cortical inhibition of intestinal motility in the squirrel monkey

Cortical control over intestinal motility was examined by stimulating the cerebral cortex and recording subsequent changes in gut volume in the chloralose-anesthetized squirrel monkey. Also, correlations were made between the cortical areas effecting changes in gut motility and those receiving sensory input from the bowel, by recording evoked potentials from the same areas following stimulation of the splanchnic nerve. It was found that: (a) intestinal motility is inhibited by stimulation of frontal polysensory cortex; (b) such inhibition does not occur following stimulation of primary sensory motor cortex; (c) visceral afferents carried in the splanchnic nerve converge with somatic inputs on the same frontal cortical area controlling gut motility; (d) the cortical control may act, at least in part, by modulation of the intestino-intestinal inhibitory reflex (I 3-R); and (e) the I 3-R in the squirrel monkey is similar to that previously described in carnivores.

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.

Adaptations to abyssal life as shown by the bivalve Abra profundorum (Smith)

Abra profundorum is widely distributed in the northern Atlantic in abyssal depths. A comparison is made between the gross morphology of A. profundorum and that of other north Atlantic species in this genus. This shows that when these species are arranged according to their depth distribution (H.W.M. to Abyssal Plain), there is a correlation between depth and the size of the gills and palps as well as the length and volume of the hind gut. In those species occurring in deep water the gill becomes much reduced in size and, apart from its respiratory function, acts essentially as a conveyer belt transporting the incoming sediment from the incurrent siphon to the pals. The palps of deep water species are enlarged and possibly this is a compensation for the loss of ciliated surface of the gills, in order to maintain the power to suck in vast quantities of bottom sediment. The hind gut becomes progressively elongated and the consequent storage of faecal material can probably be explained in terms of the increased bulk of material ingested and the necessity of ensuring that all nutritive material is extracted from deep water sediments which are poor in available organic nutritive materials.