Energy metabolism during development of eggs and larvae of gilthead sea bream (Sparus aurata)

Developing eggs and larvae of laboratory-reared gilthead sea bream (Sparus aurata) maintained in filtered seawater (40 ppt) at 18°C, were measured for oxygen uptake, ammonia excretion, contents of free amino acids (FAA), protein, fatty acids (FA) accumulated ammonia, and volumes of yolk-sac and oil globule. Absorption of the yolk coincided with the consumption of FAA and was complete ca. 100 h post-fertilisation. Amino acids from protein were mobilised for energy in the last part of the yolk-sac stage. Absorption of the oil globule occurred primarily after hatching following yolk absorption, and correlated with catabolism of the FA neutral lipids. Overall, FAA appear to be a significant energy substrate during the egg stage (60 to 70%) while FA from neutral lipids derived from the oil globule are the main metabolic fuel after hatching (80 to 90%).     

Structure of monogenean populations,ectoparasites of the gilthead sea bream Sparus aurata

In the Western Mediterranean, the gilthead sea bream Sparus aurata Linnaeus, 1758 is parasitized by two gill monogeneans, Furnestinia echeneis (Wagener, 1857) Euzet and Audouin, 1959 (Monopisthocotylea: Diplectanidae) and Sparicotyle chrysophrii (van Beneden and Hesse, 1863) Mamaev, 1984 (Polyopisthocotylea: Microcotylidae). The spatial structure of these parasitic populations were studied on the French coast in the Gulf of Lions in 1984 and 1985. The relations between the two species forming this guild have been demographically analyses. Their distribution profiles are very similar and display some stability with time, although some increasing trends are perceptible in the spring. These two monogeneans are globally frequent, but always present in only moderate intensities in infrapopulations. Recruitment of F. echeneis is independent of that of S. chrysophrii. This mode of contamination limits massive and simultaneous infestations of a single host, and interspecific competition risks are consequently considerably reduced. Our results suggest these parasites can affect the size of a natural gilthead population to only a limited degree.     

Trypsin content in intestines of herring larvae,Clupea harengus,ingesting inert polystyrene spheres or live crustacea prey

In 1986, at the Danish Institute of Fisheries and Marine Research, Denmark, Clupea harengus L. larvae from three different herring stocks were offered either non-biodegradable polystyrene spheres, nauplii and copepodites of Acartia tonsa or Artemia ssp. nauplii. Ingestion of polystyrene spheres induced trypsin secretion to a higher level than in non-feeding fish. Larvae ingesting live food of the same width as the polystyrene spheres exhibited the highest trypsin content in the intestines. Mechanisms responsible for the regulation of pancreatic enzyme secretion are discussed.     

Feeding rates and prey selectivity of planktonic decapod larvae in the Western English Channel

Meroplankton are seasonally important contributors to the zooplankton, particularly at inshore sites, yet their feeding ecology is poorly known relative to holoplankton. While several studies have measured feeding in decapod larvae, few studies have examined the feeding rates of decapod larvae on natural prey assemblages throughout the reproductive season. We conducted 8 feeding experiments with Necora puber, Liocarcinus spp. and Upogebia spp. zoea larvae collected from the L4 monitoring site off Plymouth (50°15.00′N, 4°13.02′W) during spring–summer 2009 and 2010. This period spanned moderate-to-high food availability (0.5–1.6 µg chl-a L^?1), but a great range in food composition with small cells <20 µm dominating in 2010. Daily rations averaged 17, 60 and 22 % of body C for the 3 respective decapod species. Clearance rates differed according to prey type, and all 3 decapod genera showed evidence of selection of dinoflagellates. Importantly, small cells including nano- and pico-plankton were ingested, this being demonstrated independently by flow cytometric analysis of the feeding experiments and molecular analysis. PCR-based analysis of the haptophyte portion of the diet revealed ingestion of Isochrysis galbana by decapod larvae in the bottle incubations and Isochrysis galbana and Phaeocystis globosa by decapod larvae collected directly from the field. This study has shown that pico- and nano-sized plankton form an important supplement to the diverse and variable diet of decapod larvae.     

Some effects of food density on the growth and behaviour of plaice larvae

The effect of food density on the growth, survival, and swimming activity of plaice larvae (Pleuronectes platessa L.) was investigated under controlled laboratory conditions. Suboptimal food concentrations decrease the growth of the height of the body musculature relative to length, and increase the amount of time spent searching for food. Older larvae are able to withstand much longer periods without food than young larvae. On the basis of these experiments, it is suggested that food limitation in a larval plaice population is likely to result in a concave mortality curve.     

Ontogeny of diet changes in a tropical benthic carnivorous fish, Parupeneus barberinus (Mullidae): relationship between foraging behaviour, habitat use, jaw size, and prey selection

Parupeneus barberinus forages on benthic invertebrates using a wide range of foraging modes, including vigorous digging in the substratum, resulting in considerable disturbance to the benthos. Polychaetes were the most important prey item for all size classes, but fishes less than 120 mm total length consumed more small ostracods and nematodes than did larger fishes. Fishes greater than 120 mm total length consumed mostly bivalves, and fishes over 240 mm total length consumed mostly bivalves and crabs. A morphological examination of the feeding apparatus suggested that the size of important prey items consumed was determined by gape height and jaw width. Prey available to different size classes of fishes was determined by combining information on microhabitat use, foraging behaviours, and prey volumes in the substratum. Small fishes spent more time foraging on the reef flat and slope, compared with larger fishes that foraged mostly on the reef edge and base. In addition smaller fishes foraged mostly in the upper 2 cm of sediment, whereas larger fishes often foraged to depths of 10 cm. Selection ratios showed that different size classes of fishes selectively extracted different prey items from the substratum. Small fishes showed a preference for ostracods whereas large fishes selected for bivalves and crabs. Although polychaetes were the dominant prey item for all size classes, they were consistently selected against.     

Prey selection by larval weakfish (Cynoscion regalis): the effects of prey size,speed, and abundance

We examined feeding by larval weakfish, Cynoscion regalis (Bloch and Schneider), in laboratory experiments conducted during the 1991 spawning season. under natural conditions weakfish larval development is ca. 3 wk, and we ran separate experiments with larvae of five different ages (5, 8, 11, 14, and 17 d post-hatching). We used two different size classes of rotifers (Brachionus plicatilis) and brine shrimp nauplii (Artemia sp.) as prey organisms. Contrary to results of previous research, weakfish larvae did not select prey based on size alone. When prey abundance was above 100 itemsl^-1 weakfish, larvae always chose large rotifers (length = 216 m) over small rotifers (length = 160 m). At 11 d post-hatching, larvae switched their diet from large rotifers to small brine shrimp nauplii (length = 449 m); however, when fed small rotifers and small brine shrimp nauplii the change in diet occurred at 14 d post-hatching. This pattern of selectivity was maintained in each larval age class. Early-stage larvae (5 and 8 d post-hatching) did not feed selectively when prey abundance was less than 100 itemsl^-1. Late-stage larvae (17 d post-hatching) fed selectively at abundances ranging from 10 to 10000 items^-1. Lwimming speeds of prey items, which ranged from 1 to 6 mms^-1, had no consistent effect on prey selection. These results suggest that weakfish larvae are able to feed selectively, that selectivity changes as larvae age, and that selectivity is also influenced by prey abundance.     

Interference by wood ant influences size selection and retrieval rate of prey by Formica fusca

Summary Dominance relations between the territorial wood ant Formica polyctena and the submissive F. fusca generate testable predictions on the mechanisms of their coexistence. Here I tested the influence of interference competition by the dominant F. polyctena on the foraging of F. fusca. In the presence of F. polyctena, the activity and the retrieval rate of items of F. fusca decreased significantly. When F. fusca were given a choice between small chironomids and flies a hundred times heavier they selected nearly always flies in the absence of wood ants; when disturbed F. fusca took proportionately more chironomids. In nature, irrespective of distance from the wood-ant mound the size distribution of potentially available food items was the same. F. fusca collected smaller items close to the wood-ant mound, where the density of interfering wood ants was high, than far from it. Also, F. polyctena carried larger protein items from the outskirts of its territory than from the center. The items of F. fusca were on average smaller than those of F. polyctena although the item-size overlap was substantial. When encountering a F. polyctena, those F. fusca workers carrying a fly always lost their booty to the dominant but always managed to bring the chironomids to the nest. F. fusca and F. polyctena were equally efficient in detecting single chironomids placed on the surface of ground, but the presence of either species decreased the discovery rate of the other. This implies mutual exploitation competition between the species for the locally most abundant protein resource. F. polyctena found single flies faster than F. fusca. In an earlier study I showed that close to the wood-ant mound the colony size and production of sexual offspring of F. fusca were reduced. I suggest that the suppressed colony success of F. fusca is attributable to the diminished size and decreased retrieval rate of prey items close to the woodant mound abounding with interfering wood-ant foragers.     

Relative importance of prey size and concentration in determining the feeding behaviour of the herringClupea harengus

The feeding behaviour ofClupea harengus L. in the light is dependent primarily on prey concentration. In the laboratory the fish feed by biting at low prey concentrations and by filtering at high concentrations. With the brine shrimpArtemia sp. as prey, the concentration required for the onset of filter-feeding was directly dependent on prey size, but the concentration at which 50% of feeding fish were filtering differed little between three sizes of brine shrimp (nauplii, and 2 and 4 mm larvae). When fed onCalanus finmarchicus, however, 50% of fish fed by filtering at concentrations at least six times lower than on any size of brine shrimp. Filter-feeding thresholds forC. finmarchicus were six to ten times lower than for any size ofArtemia sp. and, on the basis of biomass, approximately eight times lower than for equivalent sizedArtemia sp.     

Rearing of prawn larvae,Penaeus japonicus,fed soy-cake particles and diatoms

Soy cake^* was homogenized and filtered through an 80 mesh net to produce small, detritus-like particles. The effect of soy-cake particles, an artificial detritus, on the survival and growth of Penaeus japonicus Bate zoea was then tested. The soy cake was considered to be effective for survival and growth of the zoea. The best survival rate, 85.9%, was obtained in a tank receiving soy cake in quantities of 0.16 mg/zoea/day. An experiment was also performed to compare three kinds of food: particles of soy cake alone, diatoms (Chaetoceros rigidus) alone, and a half and half mixture of the two. The best growth, 2.49 mm, and the highest survival rate, 79.1%, were found in larvae fed the mixture of soy-cake particles and diatoms. The results thus seem to demonstrate that particles of soy cake could be usefully applied to the mass-culture of the penaeid prawn.     

Effects of prey concentration,prey size,predator life stage,predator starvation,and season on predation rates of the carnivorous copepod Euchaeta elongata

Adult females of the large carnivorous copepod Euchaeta elongata Esterly were collected from 1977 to 1980 in Port Susan, Washington, USA. Predation rates of the adult females increased with increasing prey abundance when fed the following 4 sizes of copepods: adult females of Calanus pacificus (average prosome length [PL] of 2 650 μm), adults of Aetideus divergens (PL of 1 560 μm), adult females of Pseudocalanus spp. (PL of 1 060 μm), and nauplii of C. pacificus (PL of 410 μm). Saturation feeding levels were reached when adult females of the predator were fed the small adult copepod, Pseudocalanus spp. Maximum biomass ingested of this small copepod was more than the maximum amount ingested of the larger copepods. Predation rates of the predatory copepodids at Stages IV and V also increased with increasing concentration of the 1 060 μm (PL) prey. High feeding rates exhibited by both adults and copepodids at Stage V of the predator indicate their importance as sources of mortality on populations of small copepods. Ingestion efficiency E _i (prey wholly consumed [prey attacked]^-1) varied as follows: adults of E. elongata were more efficient than copepodids of E. elongata; adults were more efficient than copepodids when ingesting smaller prey; starved adults were more efficient than fed ones; and both adults and copepodids were more efficient at low food concentrations. For adults of E. elongata, there were no marked seasonal variations in predation or respiratory rates that would represent acclimatory responses; however, small adults obtained during winter were more efficient at ingesting prey than were the larger adults gathered in summer. This seasonal variation in the efficiency of ingestion may be a useful indicator of physiological state: high E _i values could indicate that predators are starving in winter, and low E _i values could indicate that predators are satiated in summer.     

Feeding,growth, and survival of Engraulis mordax larvae reared in the laboratory

Methods are described for the successful rearing of northern anchovy larvae (Engraulis mordax Girard) on cultured foods. Larvae were fed successively on the unarmored dinoflagellate Gymnodinium splendens, the veliger of the gastropod Bulla gouldiana, and nauplii of the brine shrimp Artemia salina. Rearing containers ranging in capacity from 4.5 to 510 l were tested; the smaller ones were found to be most useful for laboratory experimentation. Irreversible starvation occurred when E. mordax were denied food for more than 1.5 days after yolk absorption. Growth rates of larval anchovies fed different diets were compared. Larvae fed G. splendens grew for 1 week at the same rate as animals fed wild plankton, but did not maintain this rate. Laboratory survival of E. mordax larvae on a diet of G. splendens alone, did not differ significantly when veligers supplemented the diet. However, when G. splendens and veligers were fed simultaneously to E. mordax larvae, growth rate was greatly improved, although still not matching the growth attained on a diet of wild plankton. Length (L) versus weight (W) analyses were made for all larvae at all diets. The results showed that weight could be calculated most accurately from length by the relationship log W=3.3237 log L-3.8205, regardless of diet.     

Feeding,food preference,and the uptake of food energy by the supralittoral isopod Ligia pallasii

Analyses of gut contents of freshly collected Ligia pallasii (Brandt) showed that the principal foods were encrusting diatoms, insect larvae, occasional members of the same species, and a variety of red and green seaweeds growing in the upper interiidal tidepool habitat. L. pallasii prefers to eat the green seaweed Ulva sp., and the brown alga Nereocystis luetkeana, when given a choice between several seaweeds, although neither of these forms is normally accessible to the isopods. The absorption (assimilation) of food-energy was 78% on a diet of Ulva and 55 to 76% on a diet of N. luetkeana—representative values for an algivorous invertebrate. A correlation analysis on the relationship of feeding preference of L. pallasii with calorific value of 7 potential seaweed foods suggested that feeding preference in this species is related to factors other than energy content of the food. Food preferences of invertebrates are discussed in relation to calorific value, accessibility, and to various nutritional factors.     

The effect of food availability,age or size on the RNA/DNA ratio of individually measured herring larvae: laboratory calibration

RNA/DNA ratios in individual herring (Clupea harengus) larvae (collected from Kiel Bay, Baltic Sea, in 1989) were measured and proved suitable for determining nutritional status. Significant differences between fed and starving larvae appeared after 3 to 4 d of food deprivation in larvae older than 10 d after hatching. The RNA/DNA ratio showed an increase with age or length of the larvae and was less pronounced in starving larvae compared to fed larvae. The individual variability of RNA/DNA ratios in relation to larval length of fed larvae and of larvae deprived of food for intervals of 6 to 9 d is presented. Based on the length dependency and the individual variability found within the RNA/DNA ratios, a laboratory calibration is given to determine whether a larva caught in the field has been starving or not. An example for a field application is shown.     

Clam predation by whelks (Busycon spp.): Experimental tests of the importance of prey size,prey density,and seagrass cover

In 57 l-m² samples within a meadow of Halodule wrightii in Bogue Sound, North Carolina, USA, densities of the clams Mercenaria mercenaria and Chione cancellata were positively associated with seagrass cover. Where seagrass was experimentally removed, marked individuals of both clam species exhibited high rates of mortality in fine sand sediments during two successive experiments spanning 13 months. In the unaltered (control) seagrass meadow, M. mercenaria density remained constant over 13 months and C. cancellata density declined at a slower rate than in the unvegetated plots. Seagrass provides these clams with a refuge from whelk (Busycon carica, B. contrarium, and B. canaliculatum) predation, the major cause of mortality and population decline in experimentally unvegetated plots. In 2 factorial field experiments in unvegetated substratum in which densities of M. mercenaria and C. cancellata were varied independently, first over 5 levels (0 X, 1/2X, 1 X, 2 X, 4 X) and subsequently over 4 levels (0 X, 1/4 X, 1 X, 4 X), there was no repeatable intra- or interspecific effect of density on percent survival, or on the rate of any mortality type. Whelk predation fell preferentially on larger size classes of both species, whereas factors which contribute to clam disappearance usually acted more intensely on smaller sizes. Experimental exclusion of large predators by caging demonstrated that even in unvegetated substratum survivorship of both clam species was high in the absence of whelks and other predators. Individuals of C. cancellata live closer to the sediment surface than those of M. mercenaria, which may explain why seagrass does not serve as effectively to protect them from whelk predation. The mechanism of whelk inhibition may depend upon sediment binding by the H. wrightii root mat, which produces a demonstrable decrease in the physical penetrability of surface sediments.     

Predator biomass,prey density,and species composition effects on group size in recruit coral reef fishes

Group incidence and size are described for recruit parrotfishes, wrasses, and damselfishes on Hawaiian reefs over 3 years (2006–2008) at sites spanning the archipelago (20–28°N, 155–177°W). Coral-poor and coral-rich areas were surveyed at sites with both low (Hawaii Island) and high (Midway Atoll) predator densities, facilitating examination of relations among predator and recruit densities, habitat, and group metrics. Predator and recruit densities varied spatially and temporally, with a sixfold range in total recruit densities among years. Group (≥2 recruits) metrics varied with time and tracked predator and recruit densities and the proportion of schooling species. Groups often included heterospecifics whose proportion increased with group size. A non-saturating relationship between group size and recruit density suggests that the anti-predator benefits of aggregation exceeded competitive costs. Grouping behavior may have overarching importance for recruit survival–even at high recruit densities–and merits further study on Hawaiian reefs and elsewhere.     

Effects of environmental conditions and prey size on locomotion behaviors of planktivorous fish

The locomotion behavior of Pseudorasbora parva was observed in laboratory under various light intensity, turbidity, structural complexity and zooplankton size, focusing on swimming speed and time of search, approach, and attack. At low prey density, the satiation level affected the swimming speed only slightly. The search speed was nearly constant regardless of the satiation level to reduce the swimming energetic cost when opportunities of encountering prey were low. However, the attack and approach speeds slightly decreased with satiation. With increasing visual and swimming conditions, the approach speed increased markedly, but the search and attack speeds did not. Although the time for the approach and attack to capture a prey did not change much with decreasing swimming and visual conditions, the search time significantly increased to compensate for the decreased swimming speed.     

Feeding behaviour of North Sea turbot (Scophthalmus maximus) and Dover sole (Solea solea) larvae elicited by chemical stimuli

The effect of chemical stimuli on the feeding behaviour of turbot (Scophthalmus maximus L.) and sole (Solea solea L.) larvae was investigated under controlled laboratory conditions. Laboratory-reared flatfish larvae exposed to chemical stimuli showed significant differences in the frequency of various behaviour patterns related to feeding (such as swimming, snapping and darting) compared to larvae exposed to blanks of filtrated seawater. The chemical substances Il-asparagine, glycine, inosine 5-monophosphate and betaine evoked the strongest behavioural responses in turbot larvae. In sole larvae the most potent substances were Il-phenylalanine, Il-lysine, Il-asparagine, inosine 5-monophosphate and betaine. These results show that feeding of turbot and sole larvae is influenced by chemosensory processes at an early larval stage, and indicate that chemoreception may be an integrated part of turbot and sole larvae feeding strategy.     

Flock size,food dispersion,and the feeding behavior of crossbills

Summary Feeding rates of five captive red crossbills (Loxia curvirostra) were measured when they were foraging alone, and in flocks of two or four on three seed dispersion patterns. On the most strongly clumped seed dispersion, individuals had higher mean feeding rates and the smallest probability of starvation when in flocks of two than when alone or in flocks of four. Individuals in flocks of four had higher feeding rates on the weakly clumped seed dispersion than on the uniform and more clumped seed dispersions; there were no food finding benefits gained from flocking on the uniform seed dispersion and aggression increased as food became more clumped. Most recent work has assumed that flocking results in higher feeding rates only because time spent vigilant is reduced. Crossbills, however, did not visit more cones per unit time as flock size increased, as would be expected if less time was spent vigilant. Thus, any reductions in vigilance as flock size increased were countered by increases in other behaviours, such as those related to aggression. Consequently, the higher mean feeding rates of crossbills in flocks than when solitary is not attributable to reduced vigilance. The increase in mean and the decline in variance of feeding rates occurred because crossbills in flocks found good patches earlier, and possible by spending less time assessing poor patches.