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.     

Diel diet shift of roach and its implications for the estimation of daily rations

In a small, 12 ha, mesotropic lake, roach Rutilus rutilus performed diel habitat shifts that clearly influenced the composition of their diet. During daytime, roach stayed in the littoral zone and concentrated on littoral prey. At night they were found in the pelagic zone, and pelagic prey items such as Daphnia spp. or Chaoborus flaricans dominated their food. On a seasonal scale, there were shifts in the importance of different food items and in the diel pattern of feeding intensity. Bioenergetics modelling in combination with an evacuation rate method for estimating daily rations allowed for changes in feeding modes to be taken into account, and so food item specific daily rations over the season could be determined. With the evacuation rate method applied on selected days, diel changes in diet compositions and feeding intensities could be quantitatively accounted for. When the 24 h integrated diet proportions were then used as an input parameter for bioenergetics modelling, food item specific consumption could be determined over the entire sampling season. The consideration of the diel diet shifts proved to be essential for the model output. If only the daytime or the night-time diet composition (derived from one single daily sampling) was taken into account for bioenergetics modelling, severe under- or overestimations of daily rations for specific food items resulted.     

食蚊鱼昼夜摄食节律观察

以分时段采样法研究入侵物种食蚊鱼的夏季昼夜摄食节律。食蚊鱼夏季种群内有雌鱼、雄鱼和幼鱼三个不同的摄食类群,这三个类群的摄食节律差异明显。雌鱼摄食节律成双峰型,第一高峰在10:00,而最高峰在22:00,此时肠道食物团平均重量11.70±11.60mg,饱满指数为190.22±155.61。幼鱼也成双峰型,分别在6:00和18:00有两个摄食高峰,以清晨6:00为最高,肠道食物团平均重1.08±1.09mg,饱满指数为128.44±105.49。雄鱼则成单峰型,摄食高峰出现午后14:00左右,肠道食物团平均重0.71±0.96mg,饱满指数为71.80±107.65。食蚊鱼不同摄食类群间的摄食高峰交错出现,是其协调种内关系,降低种内竞争的一种有效行为机制。     

Feeding behavior of leaf-like juveniles of the round batfish <Emphasis Type="Italic">Platax orbicularis</Emphasis> (Ephippidae) on reefs of Kuchierabu-jima Island,southern Japan

Feeding behavior of juvenile batfish Platax orbicularis, which presents a mimic state resembling a fallen leaf drifting on the water surface, were surveyed on reefs off Kuchierabu-jima Island, southern Japan. The fish consistently showed drifting swimming patterns on the surface during daylight hours, and fed in a picking–feeding manner on algae covering floating materials or substrates near the water surface. The fish drastically switched to planktivory during the night as they actively hunted free zooplanktonic particles through combined ram and suction feeding manners. Stomach content analysis supported that the fish adopted different feeding tactics, targeting different food items between the two diel periods. Even without an abrupt change of habitat use, due to its mimic state, juveniles of P. orbicularis explore different preys according to their daily activities.     

The structure and organization of an eelgrass fish fauna

Summary Ten species of fish made up more than 95 percent of the standing crop of the total fish assemblage of a shallow-water eelgrass meadow in southeastern Australia. The relative abundance of each species remained fairly constant from year to year during a four and a half year period. Four species were permanent residents, three moved over the meadow at high tide, and the juveniles of three species changed residence status as they grew. Most species exhibited distinct diel patterns of activity, four species were diurnal and five were nocturnal. Species foraged in different microhabitats and dietary overlap was very low amongst all but two species which had overlapping habitat, prey and prey size preferences, but had different diel activity periods. Data on production by prey and consumption of prey by these two fish species indicated that competition for food was probably responsible for the temporal separation of feeding niches. Predation by birds and fish appeared to be the major influence on the diel activity period of one fish species. The maintenance of the patterns of resource allocation among the remaining species is discussed and the organization of different seagrass fish faunas is compared.This is publication number 265 in the Ministry for Conservation, Victoria publication series. — Present address: Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada     

Food consumption and growth of larvae and juveniles of three cyprinid species at different food levels

Synopsis The relationships between food availability, consumption and growth were analyzed from the onset of feeding to an age of 90 days in three cyprinid species. Fish were held at 20 ± 0.5° C and given two (three) constant rations of approximately 30, (40) or 100% dry body weight (dbw) ind^-1 day^-1. Food consisted of living zooplankton, the size of which correlated with fish size. At high food densities consumption rates decreased rapidly with fish size in all three species. At reduced rations, fish consumed most of the food offered until they were larger than 10 mg dbw. In all species and at each feeding level daily rations consumed increased allometrically with body size. Respiration rate, expressed as routine metabolic rate differed insignificantly between the three species. At high ration levels, growth rates of small bleak, Alburnus alburnus, were distinctly lower than those of roach, Rutilus rutilus, and blue bream, Abramis ballerus. At low food supply all three species grew at similar rates. Assimilation efficiency at low food conditions was approximately twice that of the well-fed groups. If the caloric equivalents of oxygen consumption as measured in well-fed fish are applied to fish fed at low rations their energy budgets do not balance. This indicates the limitations of fish larvae in the partitioning of energy for growth or activity at such conditions.     

Short communication. Food availability and diel feeding rhythms in the marine copepods Acartia grani and Centropages typicus

The effects of food availability on the daily feeding pattern of planktonic copepods was studied for two species: Acartia grani (cultured and wild specimens) and Centropages typicus (wild specimens). Both species showed clear diel feeding rhythms at high food concentrations, with significantly higher clearance rates during night hours. However, at limiting food conditions, while C.typicus maintained its daily feeding pattern, A.grani fed continuously, with similar day and night clearance rates. These results could be explained in relation to differences in predation risks and probability of experiencing starvation episodes in their respective habitats, as well as their capacity for dampening food fluctuations. On the other hand, the maintenance (although with less intensity) of the diel feeding rhythm in A.grani, when cultured in the laboratory for long periods of time (>10 generations) and in the absence of predators, suggests the importance of the endogenous control of copepod feeding patterns.      

Feeding interactions and foraging of juvenile fish and shrimp in the estuaries of Peter the Great Bay in the summer-fall period

The feeding interrelations and foraging of juvenile fish and shrimp were investigated in estuaries of Peter the Great Bay in summer and fall 2006 and 2007. In total 3483 specimens were analyzed. The trophic spectra of 34 fish species and 3 shrimp species were described for the first time. Three trophic groups were singled out depending on differences in diet compositions: (i) detritophages (3 species of bitterlings—Acanthorhodeus sp., A. chankaensis and Rhodeus sericeus, redlip mullet Liza haematocheila and two species of shrimp-Palaemon macrodactylus and Crangon cf. septemspinosa); (ii) predators (lookup Culter alburnus and Amur catfish Silurus asotus); (iii) euryphages (28 fish species and the shrimp Palaemon paucidens). The detritus food chain was found to be the primary one in estuaries of Peter the Great Bay. Most of the species had two peaks of feeding activity each day. Values of daily feeding rations were determined for 21 fish species; these varied from 1.6% to 8.0% of body weight. Similarity in diet composition was significant only for 10% of the species, which shows a low level of competition for food in the community.     

Daily patterns of mRNA expression of two core circadian regulatory proteins, Clock2 and Per1, and two appetite-regulating peptides, OX and NPY, in goldfish (Carassius auratus)

The aim of this study was to examine the daily hypothalamic mRNA expression profiles for two core circadian regulatory proteins, CLOCK2 and PER1, and for two neuropeptides that regulate wakefulness and food intake, OX and NPY, in goldfish. The profiles were determined for fish at different nutritional states (i.e. fed or unfed on sampling day) and held at different photoperiods (i.e. 16L:8D photoperiod vs. constant light LL). Our results show that under a 16L:8D photoperiod, both fed and unfed goldfish exhibit clear antiphasic daily rhythms of hypothalamic Clock2 and Per1 mRNA expression levels, whereas under LL, daily Clock2 rhythms are seen in both fed and unfed fish while significant rhythms of Per1 mRNA expression only persist in unfed fish. In fish held under 16L:8D, but not under LL, there was significantly higher Per1 expression in fed fish at feeding time than in unfed fish. Daily variations in hypothalamic OX mRNA expression levels with peaks observed prior to both feeding time and the onset of darkness, were displayed under a 16L:8D photoperiod, whereas exposure to LL resulted in lower expression levels with no significant daily variations. Fish held under LL, but not under 16L:8D, showed significant daily variations in NPY mRNA expression with a peak prior to feeding time. Taken together, our results suggest that the mRNA expression of both appetite-regulating and circadian proteins display daily variations and that these patterns can be affected by external cues such as feeding and photoperiod.     

Food consumption of five deep‐sea fishes in the Balearic Basin (western Mediterranean Sea): are there daily feeding rhythms in fishes living below 1000 m?

Predation and food consumption of five deep‐sea fish species living below 1000 m depth in the western Mediterranean Sea were analysed to identify the feeding patterns and food requirements of a deep‐sea fish assemblage. A feeding rhythm was observed for Risso's smooth‐head Alepocephalus rostratus, Mediterranean grenadier Coryphaenoides mediterraeus and Mediterranean codling Lepidion lepidion. Differences in the patterns of the prey consumed suggest that feeding rhythms at such depths are linked with prey availability. The diets of those predators with feeding rhythms are based principally on active‐swimmer prey, including pelagic prey known to perform vertical migrations. The diets of Günther's grenadier Coryphaenoides guentheri and smallmouth spiny eel Polyacanthonotus rissoanus, which did not show any rhythm in their feeding patterns, are based mainly on benthic prey. Food consumption estimates were low (<1% of body wet mass day^?1). Pelagic feeding species showing diel feeding rhythms consumed more food than benthic feeding species with no feeding rhythms.     

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.     

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.     

Feeding dynamics,nitrogen budgets,and ecosystem role of a desert stream omnivore,Agosia chrysogaster (Pisces: Cyprinidae)

Synopsis Feeding habits, diel periodicity and total daily ingestion, and nitrogen budgets of longfin dace (Agosia chrysogaster) were examined on two occasions when food quality, but not quantity, differed. Agosia chrysogaster was found to be an opportunistic omnivore, consuming primarily insects when the preferred taxon (baetid mayflies) was abundant in the environment, but consuming primarily algae when mayfly abundance was low. Ingestion provided a better measure of diel feeding periodicity than gut fullness; feeding was diurnal on both sample dates, but more markedly so when the primary food was algae. Mean nitrogen content of algal foods was low, and A. chrysogaster apparently compensated for this by increasing its daily ingestion rate when algae were the major food. A reduction in nitrogen content of food during digestion from 4–6% (of dry mass) to less than 1% (in feces) suggested a high assimilation efficiency for nitrogen (nitrogen assimilated/nitrogen consumed = 72–78%). Populations of this abundant and successful cyprinid in Sonoran Desert streams may play an important role in ecosystem nitrogen dynamics. Nitrogen stored in fish biomass comprised 3–6% of the total nitrogen stored in Sycamore Creek, and excretion of ammonia by the fish represented 5–10% of total nitrogen uptake by algae. Such rapid recycling of usable nitrogen to primary producers is significant in this nitrogen limited stream ecosystem.     

Daily feeding rhythm and rations of Pacific salmon of the genus Oncorhynchus in the period of marine prespawning migrations

The daily feeding rhythm and rations of the humpback salmon Oncorhynchus gorbuscha, the sockeyed salmon O. nerka, and the chum salmon O. keta during marine prespawning migrations is investigated with consideration of materials collected at daily stations in waters off eastern Kamchatka in June–July 1999 and 2001 (from catches of drift nets). The bulk of humpback salmon and sockeyed salmon food consists of euphausiids, hyperiids, large copepods, pteropods, and fish juveniles. In the food of chum salmon, pteropods dominated. In a 24-h period, salmon manifest a pronounced evening peak of stomach fullness, while at night feeding discontinues. Samples collected in the morning consisted of fish who had just started feeding after the night pause. In addition to nightly period of rest, all species manifested a daytime decrease in foraging activity, though less pronounced than in the night. The daily rhythm of Pacific salmons’s feeding depends on the vertical migrations of their food items (representatives of sound-scattering layers). During the marine feeding period, the most intensive feeding is recorded in the humpback salmon and chum salmon. The daily ration of the humpback salmon is lower than that of the chum salmon but includes animals of higher food value. Due to a high digestion rate in combination with a large stomach volume, the chum salmon can consume a large quantity of low-calorific food in a short time. The daily ration of the sockeyed salmon is considerably lower than that of other salmon species.     

Diel periodicity of spawning activity in a permanently territorial damselfish: a test of adult feeding hypotheses

Synopsis Among species of damselfish in which both sexes defend individual feeding territories, spawning nearly always begins at first light and is completed within 2 h. According to the anti-competitor hypothesis, such dawn spawning occurs because it minimizes the rate of intrusion by diurnally active food competitors while the female is away from her territory. An alternative hypothesis pertaining to adult feeding biology is that dawn spawning minimizes interference with the female's own feeding activity. Diel patterns of spawning and mate-searching activity were documented for a population of garibaldi damselfish, Hypsypops rubicundus, and compared with their diel feeding patterns and those of their food competitors. Female garibaldi spawned at approximately constant levels from dawn through late afternoon and showed peaks in mate-searching activity in the late morning or in the afternoon. However, feeding activity of both female garibaldi and their food competitors increased significantly from dawn to early afternoon. Thus, there was no inverse relationship between garibaldi spawning activity and feeding activity as predicted by these hypotheses.     

Feeding ecology and daily food consumption of common sole, Solea vulgaris Quensel, juveniles on the French Atlantic coast

This study describes feeding rhythms in juvenile sole (0- and I-groups) and differences in choice of prey according to age and feeding time. In the same biotype, 0-group fish select amphipods or young opisthobranchs, whereas I-group fish eat chiefly polychaetes such as Pectinaria koreni . The daily food consumption for juvenile soles in the field (T = 19.8°C) is estimated at 7% body dry weight in 0-group and probably less in I-group. When compared with estimates from previous methods or models, these rations are intermediate between estimates from Kuipers' method, with a gastric evacuation rate ( R ) per hour representing three times the amount of food in the stomach, and those from Elliott & Persson's model with R value around 1.46.     

Thermal changes in the gastric evacuation rate of the freshwater sculpin Cottus nozawae Snyder

We experimentally measured thermal changes in the gastric evacuation rate (GER) of the freshwater sculpin Cottus nozawae Snyder under three water temperature regimes (2°, 7°, and 12°C). Laboratory experiments showed that the GER was accelerated with increasing water temperature. This result suggests that the daily food rations of fish are more likely to be underestimated at higher water temperatures if estimation is simply based on the stomach content weight alone. By comparing the GER for various fish species from subfrigid to temperate streams, we found a general pattern that the GER increases with water temperature, regardless of taxonomic group or foraging mode. However, the reaction norms of the GER against water temperature showed considerable interspecific variation. This means that stomach content weight is not comparable as a simple measure for determining the daily rations among fish species when water temperature regimes are different. To consider the temperature-dependent pattern of such a physiological phenomenon is important in understanding the feeding ecology of fishes and their roles in material cycles through food webs in aquatic ecosystems.     

Fluorescence analysis of zooplankton gut contents and an investigation of diel feeding patterns

A method is described for measurement of the in situ feeding rate of planktonic herbivores. Freshly caught Zooplankton are washed with filtered sea water and frozen. The gut contents are later analysed using acetone extracts of the entire sample. Fluorescence peaks due to ingested chlorophyll are easy to quantify for sample sizes of 20–200 animals. This method obviates some of the problems, such as confinement and previous feeding history, associated with extrapolation from laboratory experiments to field conditions. The method is illustrated by an investigation of diel feeding patterns of marine copepods. Initial results indicate the complexity of these patterns, with either a single night peak or dawn and dusk peaks for adult copepods. Diel variations in feeding activity appear to occur in addition to, but closely interacting with, the diel vertical migrations of the animals.     

Diel feeding periodicity, daily ration and prey selection of a riverine population of juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum)

The diel feeding periodicity, daily ration and prey selection of juvenile chinook salmon, Oncorhynchus tshawytscha , were studied in relation to the available prey. Maximum dry weight of food intake occurred about dawn, when mayflies were the major prey, but the greatest number of freshly eaten prey occurred during the afternoon, when chironomids and terrestrial dipterans predominated. Feeding activity at night was low, with smaller mayflies comprising up to 50% of the prey. During the day the young salmon fed selectively on chironomids and the larger mayflies, while trichopterans and terrestrial taxa were under-represented in the diet. Food consumption over the 24-h period averaged 8.3% of the fish dry body weight. Prey abundance in the drift explained about 50% of the composition of the diet. Although the fish selected larger mayflies, size apparently was not a main criterion for selection because chironomids, although smaller than mayflies, were also frequently eaten. Previous dietary experience of the fish and the diel pattern of prey abundance appear to best explain the selective feeding of juvenile chinook salmon.     

Diel variations in the assemblage structure and foraging ecology of larval and 0+ year juvenile fishes in a man‐made floodplain waterbody

This study investigated diel variations in zooplankton composition and abundance, and the species composition, density, size structure, feeding activity, diet composition and prey selection of larval and 0+ year juvenile fishes in the littoral of a man‐made floodplain waterbody over five 24 h periods within a 57 day period. There was a significant difference in the species composition of diurnal and nocturnal catches, with most species consistently peaking in abundance either during daylight or at night, reflecting their main activity period. There were no consistent diel patterns in assemblage structure or the abundance of some species, however, most likely, respectively, due to the phenology of fish hatching and ontogenetic shifts in diel behaviour or habitat use. There were few clear diel patterns in the diet composition or prey selection of larval and 0+ year juvenile roach Rutilus rutilus and perch Perca fluviatilis, with most taxa consistently selected or avoided irrespective of the time of day or night, and no obvious shift between planktonic and benthic food sources, but dietary overlap suggested that interspecific interactions were probably strongest at night. It is essential that sampling programmes account for the diel ecology of the target species, as diurnal surveys alone could produce inaccurate assessments of resource use. The relative lack of consistent diel patterns in this study suggests that multiple 24 h surveys are required in late spring and early summer to provide accurate assessments of 0+ year fish assemblage structure and foraging ecology.