The effect of feeding hierarchy on individual variability in daily feeding of rainbow trout, Oncorhynchus mykiss (Walbaum)

Three groups of rainbow trout, Oncorhynchus mykiss , (initial weight 40 g) were fed one of three rations (low, medium or high) for 73 days. Consumption by individual fish within the three ration groups was measured on four occasions (days 27, 55, 64 and 72) using radiography. Food intake by individual fish varied between days and this variability was expressed using the coefficient of variation (CV). Dominant fish within each ration group were defined as individuals with the greater share of the group meal and these fish had low CVs for food intake indicating relatively little variation in daily consumption. By contrast, the fish which had consumed a low mean proportion of the group meal displayed high CVs for food intake, indicating considerable variability in the sizes of individual meals consumed by these fish. As group ration increased, the range of meal sizes and individual CVs in daily feeding decreased, suggesting that the strength of the feeding hierarchy and the variability in individual consumption decreased as food availability increased. It is suggested that radiography can be used to assess social relationships within groups of fish allowing the assessment of feeding hierarchies in larger groups of fish than would be possible by observational techniques.     

The physiology of rainbow trout in social hierarchies: two ways of looking at the same data

Salmonids form dominance hierarchies in environments, where space or food are limiting. Our first objective was to investigate the physiology of individual rainbow trout in 4-fish hierarchies. Our second was to compare conclusions drawn from grouping physiological data on the basis of social rank with those based on relating individual physiology to individual aggressive behavior. To create a social hierarchy, groups of 4 juvenile trout were fed (1 % ration) using a darkened feeding container, twice daily (morning and evening). Each morning feeding was videotaped to record aggressive behavior, thereby facilitating the assignment of a social status rank to each fish. On days 5 and 10–11, physiological parameters were measured in fish fasted for 24 h. Social hierarchies formed in all tested groups. One fish would become dominant, whereas the three subordinate individuals would each assume a stable social rank. When classified according to this social rank, the three subordinate individuals all displayed similar physiology, different from the physiology of the dominant fish. The latter included higher ammonia excretion rate, greater protein utilization in aerobic metabolism, greater feeding, higher specific growth rate, greater increase in condition factor, and lower routine oxygen consumption rate. However, when individual aggression was taken into account, a continuous gradient was observed between aggression and physiology for most parameters, regardless of social status. These relationships could be improved by normalizing the aggression score to the overall level of aggression in each hierarchy. We argue that individual behavior should be considered instead of just social rank when studying the physiology of trout in social hierarchies.     

The effect of ration level and social rank on the development of fin damage in juvenile rainbow trout

The development and severity of fin damage was examined in groups of juvenile rainbow trout Oncorhynchus mykiss of different strength of feeding hierarchies. The development of dorsal and caudal fin damage over time was compared between four groups fed different ration levels (0·25, 0·5, 1·0 and 1·5% body weight day⁻¹) and between individuals of different feeding rank within each group. Dominance hierarchies were assessed from repeated daily measurements of food consumption of individuals using radiography. The feeding and growth data indicated that the strength of the social hierarchy weakened with increasing ration. Caudal fin damage developed with time in all groups whereas dorsal fin damage developed only under limited rations. The severity of both dorsal and caudal fin damage was significantly dependent on the ration size fed to the group, with lower ration groups sustaining more fin damage. The severity of dorsal fin erosion was greater than for the caudal fin. Within the two lower ration groups, subordinate fish suffered the most dorsal fin damage. The results suggested that the severity of dorsal fin damage within groups of juvenile rainbow trout can be used as an indicator of hierarchy Strength.     

Potential use of radiography for measuring feed intake of southern rock lobster (Jasus edwardsii)

The potential of using radiography for measuring feed intake in southern rock lobster Jasus edwardsii (Hutton) was evaluated. Lobsters (14-40 g) readily consumed feeds containing radio-opaque marker (400—450 μm). Marker particles were clearly identified in the stomach 90 min after feeding enabling feed intake to be estimated. Initially low estimates (15±17%; mean±S.D.) of feed intake (expressed as percentage of gravimetric estimates) were recorded due to loss of markers prior to ingestion. Radiographic estimates improved (100±23%; mean±S.D.) when changes to pellet diameter (1.5 mm), moisture content (11%) and binding agent (alginate) were made. Thus, estimates were dependent on pellet diameter and resistance to fragmentation prior to ingestion. To test for the presence of feeding hierarchies in groups of lobsters an experiment was conducted to examine the effect of ration level (high ration: 2.0% BW day⁻¹ and low ration: 0.2% BW day⁻¹) on intra-individual (measured as coefficient of variation for feed intake: CV_C) and inter-individual variation (measured as mean share of the group meal: MSM%). There was a significant (P<0.05) negative correlation between CV_C and MSM% for the low ration treatments which indicated that small lobsters (CV_C=114±19% and MSM%=22±10%: mean±S.D.) were less successful than large lobsters (CV_C 44±11% and MSM%=41±13%: mean±S.D.) at obtaining feed. This may be indicative of the formation of feeding hierarchies.     

摄食水平对不同性别食蚊鱼仔幼鱼生长发育的影响

在实验室27℃水温下,研究了少食、中食和饱食三个摄食水平对0至25日龄雌雄食蚊鱼(Gambusia affinis)的生长发育特征和饵料利用效率的影响。26d饲养实验结束后,对试验鱼摄食和生长指标、臀鳍分化、性成熟及饵料转换效率进行分析。结果显示:到臀鳍开始分化时,饱食组雄鱼的累计摄食总能量和生长速度开始小于雌鱼,且随日龄的增加差异加大;随摄食水平的增加,0日龄仔鱼到臀鳍分化和性成熟的时间缩短。至实验结束,各摄食组的雄鱼均形成发育完善的生殖足,性腺都达到成熟状态;而雌鱼性成熟迟于雄鱼,且其性成熟更易受到摄食水平的影响,饱食组只有约50%的个体达到性成熟,少食组的卵母细胞则均处在小生长期。随着摄食水平的增加,雌雄鱼的体长、体重和干物质特定生长率均呈明显上升趋势,而干物质饵料转化效率则呈明显下降趋势;实验结束时,雌鱼的生长指标和干物质饵料转化率均大于雄鱼。以上结果表明,伴随臀鳍的分化,食蚊鱼在摄食、生长、发育、性成熟和应对食物丰度变化上表现出显著的性别差异。       

Interindividual variations in feeding and growth in rainbow trout during restricted feeding and in a subsequent period of compensatory growth

Compensatory growth responses of rainbow trout Oncorhynchus mykiss were studied by examining food intake and growth of individual fish held within groups that were switched between regimes that involved full and restricted feeding. Restricted feeding led to marked interindividual variability in food intake, probably as a result of the establishment of feeding hierarchies. This disparity in food acquisition was reflected in highly heterogeneous growth amongst the fish fed low rations. When fish were transferred from restricted to full rations, they became hyperphagic and displayed high rates of growth. Growth compensation was most marked amongst those fish which had shown the poorest growth during the period of feed restriction. These results suggest that the feeding hierarchies established under feed restriction did not persist, but were rapidly broken down when food became increasingly available, enabling the previously suppressed fish to gain access to food and to display rapid growth.     

Effects of Food Type and Number of Feeding Sites in a Tree on Aggression During Feeding in Wild <Emphasis Type="Italic">Macaca fuscata</Emphasis>

It is important to understand the effects of ecological factors on aggression during feeding in order to link habitat characteristics to competitive regime and social relationships. Multiple habitat characteristics are likely to affect aggression, but few researchers have examined the effect of multiple factors on intragroup competition simultaneously. I examined the effect of 8 factors on aggression during feeding in wild Japanese macaques living in a coniferous forest in Yakushima: density of the tree species, feeding time, number of feeding sites within a feeding tree, number of cofeeding animals, intratree macaque density, food type, and rank and age of the focal individual. When macaques cofed with other individuals, food type, the number of feeding sites, and their interactions significantly influenced aggression. Aggression increased when macaques ate fruits/seeds versus other foods and as the number of feeding sites decreased. Primate socioecological models highlight the importance of clumped distribution of food patches as a correlate of intragroup contest. However, my study indicates that primatologists need to pay attention to the factors related to the current feeding tree—food type and feeding tree size with respect to monopolizability—in addition to the distribution of food in the entire home range.     

Feeding rank and dominance in Tilapia rendalli under defensible and indefensible patterns of food distribution

In four scatter-fed groups of Tilapia rendalli , the distribution of food between individuals was not significantly different from that expected if the food was shared uniformly between all the fish in the group for nine of the 12 radiographic assessments of feeding behaviour. Individual fish maintained the same feeding rank over time, indicating a stable feeding hierarchy, in only one of the four scatter feeding groups. In contrast, in four point source feeding groups, the distribution of food between individuals differed significantly from uniformity in 10 of the 12 radiographic assessments of feeding behaviour and stable feeding hierarchies were maintained over time in three of the four groups. Thus, scatter feeding promoted a more uniform distribution of food between individuals within the group and prevented the formation of feeding hierarchies. There was no significant correlation between individual feeding rank and dominance index in all four scatter feeding groups. In contrast, significant positive correlations were found between individual feeding rank and dominance index in all four point source feeding groups. The results of this study confirm that feeding rank can be used as a correlate of relative social status under defensible feeding conditions.     

Sex differences in diurnal rhythms of food intake in mice caused by gonadal hormones and complement of sex chromosomes

We measured diurnal rhythms of food intake, as well as body weight and composition, while varying three major classes of sex-biasing factors: activational and organizational effects of gonadal hormones, and sex chromosome complement (SCC). Four Core Genotypes (FCG) mice, comprising XX and XY gonadal males and XX and XY gonadal females, were either gonad-intact or gonadectomized (GDX) as adults (2.5 months); food intake was measured second-by-second for 7 days starting 5 weeks later, and body weight and composition were measured for 22 weeks thereafter. Gonadal males weighed more than females. GDX increased body weight/fat of gonadal females, but increased body fat and reduced body weight of males. After GDX, XX mice had greater body weight and more fat than XY mice. In gonad-intact mice, males had greater total food intake and more meals than females during the dark phase, but females had more food intake and meals and larger meals than males during the light phase. GDX reduced overall food intake irrespective of gonad type or SCC, and eliminated differences in feeding between groups with different gonads. Diurnal phase of feeding was influenced by all three sex-biasing variables. Gonad-intact females had earlier onset and acrophase (peak) of feeding relative to males. GDX caused a phase-advance of feeding, especially in XX mice, leading to an earlier onset of feeding in GDX XX vs. XY mice, but earlier acrophase in GDX males relative to females. Gonadal hormones and SCC interact in the control of diurnal rhythms of food intake.     

The influence of ration size and feeding frequency on ammonia excretion by juvenile Atlantic cod, Gadus morhua L.

Small groups of juvenile Atlantic cod, Gadus morhua L., were kept at 14°C in through-flow tanks and were fed known quantities of a compounded diet of natural food. The cod were fed single and multiple meals with ration size in the range 0.5 to 4.1% of total wet fish body weight. Ammonia production in each feeding experiment was monitored continuously.
For single-meal experiments, significant relationships were derived between ration size and (a) total ammonia excreted, (b) total exogenous ammonia excreted above endogenous excretion levels, (c) duration of the elevated phase of ammonia excretion, (d) maximum rate of ammonia excretion, and (e) time delay after feeding to reach maximum rate of ammonia excretion. Relationships between nitrogen loss as ammonia and nitrogen intake were examined and estimates of endogenous excretion rate and maintenance ration made.
Repetitive feeding resulted in cyclical variation in ammonia excretion. At the lowest ration size, ammonia excretion rates had nearly returned to the pre-feeding level within 24 h. At higher feeding levels, the effect of each successive meal tended to be cumulative, resulting in increasingly higher ammonia excretion rates which only stabilized towards the end of the experiments.     

Impact of Environmental Disturbance on the Stability and Benefits of Individual Status within Dominance Hierarchies

Changes in environmental conditions affect social interactions and thus may modify an individual's competitive ability within a social group. We subjected three‐spined sticklebacks, Gasterosteus aculeatus, housed in groups of four individuals, to environmental perturbations to assess the impact on dominance hierarchy stability. Hierarchy stability decreased during increased turbulence or lowered water levels (‘simulated drought’) whereas control hierarchies became more stable in a constant environment. The dominant individual either became more aggressive and remained dominant during the environmental manipulation or was usurped by a lower rank member. Only simulated drought affected rates of aggression where levels of aggression were higher after the water level was dropped which may be the result of an increased encounter rate in these conditions. When there were large size differences between the group members, the dominant individual performed the greatest amount of aggression and ate the largest proportion of food and there was little aggressive behaviour from the lower ranks. In groups of similar‐sized individuals, aggression was much higher. The benefit of being dominant was to gain weight over the experimental period whereas ranks 2 and 3 lost weight. The lowest rank, 4, actually gained weight over the experimental period. This study suggests that it would benefit an individual to be dominant, highly aggressive and gain weight or be submissive, avoid aggressive interactions and, by sneakily obtaining access to food, also gain weight. Altering environmental conditions has a profound effect on social behaviour in this study.     

Effect of experimental conditions on the stomach evacuation of Coregonus lavaretus L.

The gastric evacuation of juveniles of Coregonus lavaretus L. fed on living Daphnia pulicaria was investigated. Three successive stages of stomach evacuation were observed when one meal per day was given: (i) a lag phase between the end of food intake and the beginning of stomach evacuation, (ii) a linear reduction of stomach content, (iii) a long residence time for food relics in the stomach. The initial stomach content and the stomach evacuation time are correlated positively. The stomach content increased during feeding when three meals day ⁻¹ were provided and it decreased when no food was available. During the course of an experiment the highest stomach content found increased with increasing daly ration. Excess feeding resulted in a low stomach content similar to that found with rations about 30–50% of the maximum daily food intake. Therefore the daily food intake cannot be determined by the single parameter of stomach content alone. Identical initial stomach contents showed significantly higher stomach evacuation rates under three meals day⁻¹ conditions than under one meal day⁻¹ conditions.     

Effect of feeding frequency on growth, feed utilization, and size variation of juvenile gibel carp (Carassius auratus gibelio)

Juvenile (3.0 ± 0.2 g) gibel carp (Carassius auratus gibelio) were fed to satiation for 8 weeks to investigate the effect of feeding frequency on growth, feed utilization and size variation. Five feeding frequencies were tested: two meals per day (M2), three meals per day (M3), four meals per day (M4), 12 meals per day (M12) and 24 meals per day (M24). The results showed that daily food intake increased significantly with the increase in feeding frequency and there was no significant difference between daily food intakes in M12 and M24 treatments. Growth rate, feed efficiency increased significantly with increasing feeding frequencies. Size variation was not affected by feeding frequency. Apparent digestibility of dry matter was not influenced by feeding frequency, while apparent digestibility of protein and energy increased significantly at high feeding frequencies. The feeding frequency had no significant effect on the moisture, lipid, protein, or energy contents of gibel carp, while the ash content decreased with increased feeding frequency. It was recommended that 24 meals per day was the optimal feeding frequency for juvenile gibel carp.     

Using training to moderate chimpanzee aggression during feeding

The effects of human and nonhuman primate interactions on the well-being of captive nonhuman primates have been studied less rigorously than other forms of environmental improvement. Human intervention might be used to moderate severe aggression of socially housed animals at feeding times, one of the most common behavioral management problems. In this study, positive reinforcement training techniques were applied to reduce a dominant male chimpanzee's aggression and chasing during meals. Verbal commands and food reinforcers were used to train him to sit and remain seated while other group members received and ate their share of produce. Observational data were collected recording all instances of agonism in the group during periods when meals were fed and during times when no meals were offered, both before and after the training was accomplished. Multivariate analysis of variance for repeated measures results indicated that the training program successfully reduced the group's incidence of displaying, submission, and aggression during feeding periods. This effect was specific to the times meals were fed; there was no generalized reduction in the group's agonism after the training. This study exemplifies the use of positive reinforcement techniques to modify chimpanzee social dynamics during a problematic situation and of observational data to evaluate quantitatively the behavioral effects of the training. Training can be employed to help solve behavioral management problems among socially housed animals, and it can help improve the psychological well-being of captive chimpanzees. © 1994 Wiley-Liss, Inc.     

Diel activity and home range size in relation to food supply in a drift-feeding stream fish

Individuals within a species often compete for resources inboth space and time. In dominance hierarchies individuals withthe greatest competitive ability will occupy prime locationsduring optimal periods. We compared spatial and temporal useof habitat, aggression, and feeding success among giant kokopu(Galaxias argenteus) in dominance hierarchies under normal andreduced food supply. Under normal food supply conditions dominantfish were predominantly nocturnal and maintained large homeranges at night. Conversely, subdominant fish were diurnal andoccupied large home ranges by day but were generally not observedat night. When the food supply was limited, the utilizationof pools was determined by social rank. Dominant fish from eachpool increased diurnal activity, home range size, aggressiveness,and the capture of food items offered by day while simultaneouslyreducing the spatial and temporal activity and habitat use ofsubdominant fish. These results indicate that behavioral changesin large dominant fish influence and reduce the amount of resourcesavailable to subdominant fish.     

Effects of size asymmetry on aggression and food acquisition in Arctic charr

The feeding rate of a group (DS) of two small, two medium and two large 1+ Arctic charr Salvelinus alpinus was higher than in a group of six fish of the same size (SS), suggesting that size distribution had an effect on feeding behaviour, with a correlation between the size of the fish and the amount of food eaten–the largest fish eating the most. Against predictions, rate of aggression was not higher in the SS groups; rather there was a modest tendency of higher aggression among individuals in the DS groups.     

Eating meals before wheel-running exercise attenuate high fat diet-driven obesity in mice under two meals per day schedule

Mice that exercise after meals gain less body weight and visceral fat compared to those that exercised before meals under a one meal/exercise time per day schedule. Humans generally eat two or three meals per day, and rarely have only one meal. To extend our previous observations, we examined here whether a “two meals, two exercise sessions per day” schedule was optimal in terms of maintaining a healthy body weight. In this experiment, “morning” refers to the beginning of the active phase (the “morning” for nocturnal animals). We found that 2-h feeding before 2-h exercise in the morning and evening (F-Ex/F-Ex) resulted in greater attenuation of high fat diet (HFD)-induced weight gain compared to other combinations of feeding and exercise under two daily meals and two daily exercise periods. There were no significant differences in total food intake and total wheel counts, but feeding before exercise in the morning groups (F-Ex/F-Ex and F-Ex/Ex-F) increased the morning wheel counts. These results suggest that habitual exercise after feeding in the morning and evening is more effective for preventing HFD-induced weight gain. We also determined whether there were any correlations between food intake, wheel rotation, visceral fat volume and skeletal muscle volumes. We found positive associations between gastrocnemius muscle volumes and morning wheel counts, as well as negative associations between morning food intake volumes/body weight and morning wheel counts. These results suggest that morning exercise-induced increase of muscle volume may refer to anti-obesity. Evening exercise is negatively associated with fat volume increases, suggesting that this practice may counteract fat deposition. Our multifactorial analysis revealed that morning food intake helps to increase exercise, and that evening exercise reduced fat volumes. Thus, exercise in the morning or evening is important for preventing the onset of obesity.     

Maximum daily ration and the pattern of food consumption in haddock, Melanogrammus aeglefinus (L.), and dab, Limanda limanda (L.)

Food intake was measured under conditions of continuous food availability for haddock, Melanogrammus aeglefinus (L.), and dab, Limanda limanda (L.). Haddock consumed approximately 75% of all food during the day, with a peak of feeding at dusk and an inferred peak at dawn; peaks of feeding were associated with larger meals. By contrast, dabs were mainly night-time feeders with daily consumption rates that were approximately 40% lower than those shown by haddock. Comparison of haddock maximum daily ration with published estimates of consumption in the wild indicate that wild haddock feed at between 15 and 22% of their maximum capacity. Using published data on gastric evacuation, the relationship between meal size and stomach residuum was investigated. There was no detectable relationship between these two variables.     

Spatial distribution patterns of sheep following manipulation of feeding motivation and food availability

We hypothesised that (i) increased feeding motivation will cause sheep to move further apart as a result of individuals trying to find food and (ii) in conditions of high food availability, sheep will move less and show greater social attraction. The effects of both feeding motivation and food availability on spatial distribution was examined in eight groups of food-deprived (high feeding motivation) and satiated (low feeding motivation) sheep in good or poor food resource plots in a 2 × 2 design. Distance travelled was assessed using Global Positioning System collars, grazing time using scan sampling and social cohesion using proximity collars that record the number and duration of encounters within 4 m. Food-deprived sheep in the good-resource plots grazed the most, whereas satiated sheep in the poor-resource plots grazed the least (P = 0.004). Food deprivation had no significant effect on the number or duration of encounters and feeding motivation appeared to have little effect on spatial distribution. Contrary to expectation, sheep had more encounters (P = 0.04) of a longer total duration (P = 0.02) in poor-resource plots than in good-resource plots, indicating that sheep were showing more social cohesion if food was scarce. Our findings suggest that when food is scarce, animals may come together in an attempt to share information on food availability. However, when a highly preferred food is abundant and well dispersed, they may move apart in order to maximise the intake. It is concluded that the particular details of our experiment, namely the even distribution or absence of a highly preferred food, affected spatial distribution patterns as sheep tried to find this food and maximise the intake.