Entrainment of Circadian Wheel-Running Rhythms of the Northern Brown Bandicoot, Isoodon macrourus, by Daily Restricted Feeding Schedules

Northern brown bandicoots (Isoodon macrourus) were subjected to restricted feeding for 3 h in the middle of the light period of a 14: 10 light/dark cycle and immediately following this in constant dark. When feeding was restricted to the middle of the light period of the light/dark cycle, all bandicoots maintained a nocturnal activity rhythm. In addition to the nocturnal rhythm, a few bandicoots showed meal-anticipatory activity during the light period. In bandicoots that did not show meal-anticipatory activity, diurnal activity was sometimes evident either during or shortly after the daily meal time. The observation of meal-anticipatory activity in some bandicoots suggests that this species may have a mechanism separate from the light-entrainable mechanism that allows the daily anticipation of periodically available food sources. In the next stage of the experiment, which was in constant dark, the meal was presented at the same time of day as it had been in the previous stage. In all bandicoots, the previously light-entrained component of activity free-ran and was eventually affected by the restricted feeding schedule to some degree. Bandicoots showed weak entrainment and relative coordination, suggesting that restricted feeding is a weak zeitgeber in this species. Evidence also suggesting that two separate but coupled pacemakers control the activity rhythms of the bandicoot was that (a) bandicoots simultaneously showed free-running light-entrainable rhythms and meal-entrained anticipatory rhythms; (b) in several bandicoots, the light-entrainable rhythm was phase advanced when it free-ran through the meal time; and (c) in one bandicoot, meal-entrained anticipatory activity was forced away from the meal time when the previously light-entrained component of activity free-ran through it.     

Histamine Receptor and its Regulation of Energy Metabolism

In a series of studies on brain functions of histamine, probes to manipulate activities of histaminergic neuronal systems were applied to assess histaminergic function in non-obese normal, and lean and obese Zucker rats. Food intake was suppressed by both activation of H₁-receptors and inhibition of H₃-receptors in the ventromedial hypothalamic nucleus (VMH) and the paraventricular nucleus, each of which is a satiety center. Feeding circadian rhythm was decreased in its amplitude through histaminergic modulation in the hypothalamus. Histamine neurons in the mesencephalic trigeminal nucleus (Me5) were involved in regulation of masticatory functions, particularly eating speed, while histamine-containing neurons in the VMH controlled intake volume of meals. Energy deficiency in the brain enhanced satiation through histaminergic activation of VMH neurons, which in turn produced glycogenolysis in the hypothalamus to maintain homeostatic control of glucose supply. A very-low-calorie conventional Japanese diet, which is a fiber rich and low energy food source, enhanced satiation by increased mastication and because of the low energy supply of the diet. Hypothalamic histamine neurons were activated by high ambient temperature and also by interleukin-1β, an endogenous pyrogen, to maintain homeostatic thermoregulation. Behavioral and metabolic abnormalities of Zucker obese rats were mediated by a deficit in hypothalamic neuronal histamine, and the Zucker rat was evaluated as an animal model of histamine deficiency. Transplantation of the lean fetal hypothalamus into the third cerebroventricle of host obese Zuckers attenuated the abnormalities.     

Sexual differences in natal dispersal and philopatry of the grey-sided vole

The natal dispersal distance of the grey-sided vole,Clethrionomys rufocanus (Sundevall), was measured in a large outdoor enclosure (2.1 ha) in Hokkaido, Japan. Voles in about half of the enclosure (1 ha) were fed. Distance from the natal site to the site of reproduction was significantly greater in males (64.9 m) than in females (35.3 m). In males, 24.8% settled within one home range length of their natal site and 49.6% settled further than two range lengths from their natal site. In femles, the respective percentages were reversed: 51.2% and 22.0%. The timing of large movements (≥50 m) was related to body mass in both sexes. The population density was always higher on the fed grid than on the control grid, which resulted in the frequency of large movements being greater on the fed grid that on the control grid. Thus, the percentage of voles performing a large movement was not different between the grids in both sexes.     

State-dependent feed acquisition among two strains of hatchery-reared Arctic charr

The effects of genetic and environmental factors on aggression and feeding hierarchies were studied using X-radiography to measure food intake by hatchery-reared individuals of two strains (Hammerfest and Svalbard) of Arctic charr Salvelinus alpinus . A reduction in food rations and/or water current speed increased intraspecific aggression, and both factors led to increased interindividual variability in food intake, increasing the coefficient of variation (CV). Following a return to pre-manipulation conditions, CVs decreased to their original level. In control groups, CVs and share of group meals were stable throughout the experiment. The increase in CVs following manipulation was the result of a small number of dominant individuals obtaining a high share of the meal. Restriction in food ration affected share of meals, specific growth rates and the frequencies of non-feeding fish, while reductions in water current speed affected only share of meals. Feeding hierarchies were size-dependent in the control groups. In contrast, no relationships between body weight and feeding rank were evident in groups in which food ration or water current speed were reduced. A small, but consistent, difference was revealed in feeding hierarchy responses between the two strains.     

Differences in feeding between 1+ and 2+ hatchery brown trout exposed to low water temperature

Both 1 + and 2+ brown trout fed during the day and at night when held in hatchery tanks at low temperatures (2·7–3° C). Over 60% of the daily ration was consumed during daylight hours, but there were differences in feeding behaviour between fish of the two age groups: the 1 + trout had greater feeding activity at night than the 2+ fish.     

Daily feeding rhythms in Atlantic salmon II: size-related variation in feeding patterns of post-smolts under constant environmental conditions

Previous studies of feeding rhythms in post-smolt Atlantic salmon Salmo salar have produced variable results. Therefore, the present study was performed to clarify the source of these differences and to examine size-related variation in daily feeding patterns. A small group of hatchery reared post-smolts was kept in an indoor seawater tank under conditions of constant photoperiod and light intensity, and negligible diurnal variation in water temperature. Feeding responses were monitored by video camera throughout the day. The resultant feeding pattern for the population mirrored an earlier study, with the highest levels of feeding activity in the early morning and late evening. Differences between this and other studies may be due to variation in climate, season or life-history stage. Daily feeding patterns were size-dependent. The largest fish fed at a relatively constant level through the day, medium-sized fish fed in a pattern similar to that described above for the population and small fish fed most at first and last light. These differences were due probably to the effect of competitive interactions upon fish of different sizes.     

The feeding response of diploid and triploid Atlantic salmon and brook trout

Pair and group experiments were conducted to determine whether differences exist in feeding success between juvenile diploid and triploid salmonids in a competitive situation. In the pair experiments, 22 pairs (one diploid and one triploid) of size-matched Quebec-strain brook trout Salvelinus fontinalis (7·2–46·3 g) were fed an unlimited number of pellets three times a day for 5 days. Dominance was assigned to the fish which ate the most pellets within each pair. In the group experiments, groups of three diploid and three triploid size-matched fish were fed a restricted ration three times a day for 5 days. Hierarchical rank within the group was assigned based on the number of pellets consumed by each fish. The group experiment was repeated 10 times with Atlantic salmon Salmo salar (5·1–62·7 g), Quebec-strain brook trout (11·8-110·8 g), and large UNB-strain brook trout (18·2–33·0 g), and 12 times with smaller UNB-strain brook trout (0·6–2·0 g). A statistically significant difference in rank between ploidies was found only for the smaller UNB-strain brook trout in the group experiments, with diploids dominant over triploids. This suggests that there may be a difference in competitive feeding success between diploid and triploid brook trout early in development, but that this difference diminishes as the fish grow.     

Feeding strategy and growth of cyprinids in the littoral zone of Lake Balaton

The growth, diet and feeding strategy of five phytophil or phytolithophil species of Cyprinidae from the littoral habitats of Lake Balaton were investigated by examining their scales and foregut contents. The relationships between the total anterior radii of scales and the standard lengths were represented best by a power function for white bream Blicca bjoerkna , and linear functions for common bream Abramis brama , roach Rutilus rutilus and wild goldfish Carassius auratus gibelio , respectively. The backcalculated mean lengths for the first age groups of common bream, white bream and roach did not differ statistically from those obtained by direct observation on 0 group fish in late November 1995. Compared to other waters, common bream grows slowly, wild goldfish and roach rapidly, while the growth rate of white bream can be considered of medium speed in Lake Balaton. Common bream showed a generalized feeding pattern, consuming mainly chironomid larvae, detritus and Corophium curvispinun . Roach showed a clear shift between specialization for Dreissena and algae. Despite the dense population of D. polymorpha in the lake, the significance of the herbivorous adaptation of roach has not yet been made clear. Wild goldfish consumed mainly detritus but, in the open water region, it shifted to zooplankton. White bream preyed chiefly on D. polymorpha , but showed a mixed feeding pattern and utilized most of the available food resources. Carp had the most specialized feeding strategy and preyed mainly on D. polymorpha . According to the discriminant analysis, the five cyprinids exhibited significant food resource partitioning.     

Semi-mass culture of the dinoflagellate Gymnodinium splendens as a live food source for the initial feeding of marine finfish larvae

A technique was developed for the semi-mass culture ofthe unarmored dinoflagellate, Gymnodiniumsplendens under laboratory conditions. A maximumcell density of 4600 to 6800 cells ml^–1 was observedwithin 8 to 11 days of culture. An initial feedingtest for 8 days with three important marine finfishlarvae showed that red spotted grouper, Epinephelus akaara preferred G. splendensfed 200 cells ml^–1 with 44% survival. The Japanesestripe knife jaw, Oplegnathus fasciatus,attained 22% survival fed a combination of G. splendensand rotifers (200 cells ml^–1 and 5ind. ml^–1, respectively). Red sea bream, Pagrusmajor larvae did not respond well to the initialfeeding of G. splendens alone. Red seabream were observed to be solely dependent on rotifers(5 ind. ml^–1) as initial food. Gymnodiniumsplendens may be used as a live food in the initialfeeding of red spotted grouper larvae (E. akaara) toreduce mortality and to further enhancegrowth during the critical first few days ofrearing.     

FEEDING IN PERANEMA TRICHOPHORUM REVISITED (EUGLENOPHYTA)1

Feeding in Peranema trichophorum (Ehrenberg 1838) Stein 1878 was first observed over a century ago, yet there is still contention over how the feeding apparatus is used in feeding. Using video microscopy and scanning microscopy, this study documents two types of feeding. Peranema may engulf prey cells whole. Immotile cells are preferred, but moving cells occasionally are engulfed. Details of the early stages of engulfment are presented using scanning electron microscopy. A second method of feeding begins with the attachment of Peranema to a prey cell. The rods of the feeding apparatus then are repeatedly scraped over the surface of the prey until a tear occurs in the cell. The feeding apparatus is inserted into the opening and the internal cell contents are sucked out. The anterior flagellum is inserted into the prey to help remove the cell's contents.