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.     

Herring (Clupea harengus) filter-feeding in the dark

The behaviour of juvenile herring (Clupea harengus L.) feeding on Artemia sp. nauplii in both light and dark was recorded using an infra-red-sensitive television-recording technique. In the light, two modes of feeding were observed, particle biting and filtering, but in the dark only filtering was observed. Marked differences in swimming behaviour were seen between light and dark. In the light, the fish continued to school while feeding in both modes; in the dark, the school dispersed, the fish swam slower in tight circular paths and fed only by filtering. In the dark, filtering fish swam faster (0.11 m s^-1) than non-filtering fish (0.07 m s^-1). In the light, no difference in speed was measured between filtering and non-filtering fish (0.34 m s^-1). Owing to the lower filtering speeds in the dark, the removal rate of nauplii from the water was much lower than in light, except in the highest prey concentrations. This suggests that if night-time filter-feeding takes place in the sea, it will be of importance only when exploiting dense patches of food.     

Effect of light intensity on activity and food-searching of larval herring,Clupea harengus: a laboratory study

Larvae of Clupea harengus were reared from spawning herring caught in March 1982 and 1983 in the Firth of Clyde, Scotland. An infra0red observation technique was used to record the behaviour of larval herring both in shallow dishes using a top view and in a tank 2 m deep using a side view. The amount of time larvae spent swimming, which was minimum in complete darkness, increased with increasing light intensity and as the larvae grew. Maximum swimming speeds of feeding larvae were recorded at light intensities between 10 and 100 lux. The presence of food organisms (Artemia sp., Brazilian strain) at light intensities below the feeding threshold (0.1 lux) caused an increase in the proportion of time spent active, but light intensities above the threshold had different effects, depending on developmental stage: larvae of 12 mm increased swimming speed, but 21 mm larvae decreased speed. In the 2 m deep tank in darkness, larvae displayed inactive periods wherein they sank head first, interspersed with periods of upward swimming. As light intensity increased, vertical swimming was replaced by horizontal swimming. These results are discussed with reference to food searching and vertical migration of larval herring in the sea.     

Effects of various diets on the nutritional value of Artemia sp. as food for the prawn Penaeus monodon

The nutritional value of Artemia sp. as food for marine fish and crustacean larvae has been linked to the level of its polyunsaturated fatty acid (PUFA) content. Experiments in August 1984 were conducted to determine the effects of various artificial diets and algae on fatty acid composition of PUFA-deficient Artemia sp. (Utah GSL strain) and their resulting value as food for postlarvae of the prawn Penaeus monodon (Fabricius). Nauplii of the brine shrimp were grown on extracts of corn, copra, soybean and rice bran containing precursors (C18) to long-chain PUFA and also on algal species containing different levels of long-chain PUFA (C20). The nauplii were then used as food for P. monodon postlarvae. The results revealed that absence of C20 polyunsaturates from the feeds and their presence in the algae were reflected in the polyunsaturated fatty acid content of the tissues of Artemia sp. When fed with brine shrimp fed on algae, P. monodon displayed better postlarval survival and significantly higher growth; related to the content of polyunsaturated fatty acids in Artemia sp. A practical feeding approach in prawn hatcheries would be to grow Artemia sp. on a cheap diet such as rice bran, and then to enhance its nutritional value with a diet high in PUFA prior to harvesting, in order to improve hatchery production.     

Biochemical composition and digestive enzyme activity in larvae and postlarvae ofPenaeus japonicus during herbivorous and carnivorous feeding

The growth, survival, digestive enzyme activity and biochemical composition ofPenaeus japonicus (Bate) larvae and postlarvae were measured under three feeding regimes. Larvae were reared through the protozoeal stages usingChaetoceros gracilis. From the first mysis stage, three feeding regimes were used; (A)C. gracilis plusArtemia sp. nauplii, (B)Artemia sp. nauplii alone or (C)C. gracilis alone. No significant difference was found in growth, survival, protein content or lipid content of postlarvae from the treatments receiving the single-feed type, despite the low protein (7%) and highly unsaturated fatty acid content of the alga. Growth of larvae receiving the mixed diet was significantly higher than in the other treatments. Trypsin activity was more strongly influenced than amylase activity by dietary treatment, and differences in the ratio of these enzymes between treatments suggest independent control of their secretion. Trypsin activity recorded in larvae feeding onC. gracilis was up to six time higher than in larvae feeding onArtemia sp. nauplii, apparently in response to the low protein content of the alga. Larvae receiving the mixed diet exhibited an intermediate level of trypsin activity; it is suggested that the ingestion of algae is necessary for optimal assimilation of the zooplankton component of the diet.     

Effects of water motion and prey behavior on zooplankton capture by two coral reef fishes

Water motion is an important factor affecting planktivory on coral reefs. The feeding behavior of two species of tube-dwelling coral reef fish (Chaenopsidae) was studied in still and turbulent water. One species of blenny, Acanthemblemaria spinosa , lives in holes higher above the reef surface and feeds mainly on calanoid copepods, while a second, A. aspera , lives closer to the reef surface, feeds mainly on harpacticoid copepods, and is exposed to less water motion than the first. In the laboratory, these two blenny species were video recorded attacking a calanoid copepod ( Acartia tonsa, evasive prey) and an anostracan branchiopod (nauplii of Artemia sp., passive prey). Whereas A. spinosa attacked with the same vigor in still and turbulent water, A. aspera modulated its attack with a more deliberate strike under still conditions than turbulent conditions. For both fish species combined, mean capture success when feeding on Artemia sp. was 100% in still water and dropped to 78% in turbulent water. In contrast, when feeding on Acartia tonsa, mean capture success was 21% in still water and rose to 56% in turbulent water. We hypothesize that, although turbulence reduces capture success by adding erratic movement to Artemia sp. (passive prey), it increases capture success of Acartia tonsa (evasive prey) by interfering with the hydrodynamic sensing of the approaching predator. These opposite effects of water motion increase the complexity of the predator-prey relationship as water motion varies spatially and temporally on structurally complex coral reefs. Some observations were consistent with A. aspera living in a lower energy benthic boundary layer as compared with A. spinosa: slower initial approach to prey, attack speeds modulated according to water velocity, and lower proportion of approaches that result in strikes in turbulent water.Communicated by P.W. Sammarco, Chauvin     

Digestive mechanics and gluttonous feeding in the feather starOligometra serripinna (Echinodermata: Crinoidea)

The movement and digestion of food in the gut ofOligometra serripinna (Carpenter) were studied at Lizard Island (14°3842S; 145°2710E) in the austral winter of 1986. Feather stars in the laboratory were fed a brief, small meal of brine shrimp nauplii and killed at increasing time intervals thereafter. Histological reconstructions showed that the ingested nauplii progressed along the digestive tract surprisingly quickly. Some nauplii were found in the mid and hind intestine in only 30 min, and all of the nauplii had reached the hind intestine and rectum in 1 h. Digestion of the nauplii had started at 1 h, and only a few fragments of naupliar exoskeleton remained in the hind intestine and rectum 5 h after the start of feeding. Videotape analysis showed that no fecal pellets were released during this experiment. In the natural environment ofO. serripinna, ingested particles may similarly be transported quickly to the hind part of the gut and digested there — when feather stars were fixed in the field, most of the gut contents were found in the hind intestine and rectum.O. serripinna, which efficiently rejects inert particles before they are ingested, usually defecates infrequently (probably not more than once over a span of many hours) and differs from some other feather stars that ingest numerous inert particles and defecate much more frequently. When specimens ofO. serripinna were fed continuously on brine shrimp nauplii,Artemia sp. (San Francisco strain), in the laboratory, the feather stars fed gluttonously, packing their guts with several hundred nauplii in 1 to 2 h. Thereafter, superfluous feeding began (i.e., further ingestions appeared to force undigested nauplii, some of them still living, out of the anus). These observations suggest thatO. serripinna usually feeds at relatively modest rates in its natural habitat, but can feed gluttonously to take advantage of infrequent patches of highly concentrated, nutritious particles (e.g. copepod swarms, migrating demersal zooplankton, and invertebrate gametes from mass spawnings). It is likely that such patches of nutritious particles are usually small enough to drift out of reach of the feather stars before gluttonous feeding proceeds to superfluous feeding. Opportunities for superfluous feeding in nature are probably very infrequent (e.g. ingestion of coral gametes and embryos after a mass spawning), and the feather stars evidently have no behavior that stops further ingestions after the gut becomes filled to capacity.     

A study of the variations in lipid levels,lipid class composition and fatty acid composition in the first stages ofArtemia sp.

The lipid class composition and the fatty acid composition of total lipids of the cysts, newly hatched nauplii and 24-h-old metanauplii of a Spanish parthenogenetic diploid strain ofArtemia sp. were studied. Substantial differences in the total lipid level occurred among these stages, with a marked increase from the cyst to the nauplii being followed by a decrease in the metanaupliar stages. This variation affected the absolute levels (mg/g dry wt) of the total lipid classes and individual fatty acids, although the percent composition of the fatty acids in total lipid was essentially unchanged. An exception occurred during hatching in that the percentages of 16:0 and 16:1n-7 in total lipid decreased whereas that of 20: 5n-3 increased. The lipid classes showed higher variation than the fatty acids both in absolute and in relative terms, and in particular, the ratio of phosphatidylcholine:phosphatidylethanolamine decreased progressively from cysts to nauplii and metanauplii. The implications of these findings for the use ofArtemia sp. as a larval feed in aquaculture are considered.     

Life cycle ofRhopilema nomadica: a new immigrant scyphomedusan in the Mediterranean

Rhopilema nomadica is an Indopacific scyphomedusan, which has migrated into the eastern Mediterranean in recent years. Large aggregations of the medusae were recorded in Haifa Bay, Israel, reaching 5.5×10⁵ medusae per square nautical mile during summer 1989. The life cycle ofR. nomadica from planula to young medusa is described. Fertilization is external and planulae are formed within a few hours at 20°C. After settlement, polyps were fed withArtemia sp. nauplii and developed into polydisc strobilae within 45 d. The strobilation process was completed within 7 d, and the liberated ephyrae developed into young medusae within 2 mo. Asexual reproduction occurred mainly via podocyst formation. The population explosion ofR. nomadica could be attributed to its high reproductive potential.     

Electrophoretic survey of genetic variation in Pecten maximus,Chlamys opercularis,C. varia and C. distorta from the Irish Sea

Food selection by young larvae of the gulf menhaden (Brevoortia patronus) was studied in the laboratory at Beaufort, North Carolina (USA) in 1982 and 1983; this species is especially interesting, since the larvae began feeding on phytoplankton as well as microzooplankton. When dinoflagellates (Prorocentrum micans), tintinnids (Favella sp.), and N1 nauplii of a copepod (Acartia tonsa) were presented to laboratory-reared, larval menhaden (3.9 to 4.2 mm notochord length), the fish larvae ate dinoflagellates and tintinnids, but not copepod nauplii. Larvae showed significant (P<0.001) selection for the tintinnids. Given the same mixture of food items, larger larvae (6.4 mm notochord length) ate copepod nauplii as well as the other food organisms. These feeding responses are consistent with larval feeding in the northern Gulf of Mexico, where gulf menhaden larvae between 3 and 5 mm in notochord length frequently ate large numbers of dinoflagellates (mostly P. micans and P. compressum) and tintinnids (mostly Favella sp.), but did not eat copepod nauplii. As larvae grew, copepod nauplii and other food organisms became important, while dinoflagellates and tintinnids became relatively less important in the diet. Since the tintinnids and nauplii used in the laboratory feeding experiments were similar in size as well as carbon and nitrogen contents, the feeding selectivity and dietary ontogeny that we observed were likely due to a combination of prey capturability and larval fish maturation and learning.Contribution No. 5575 of the Woods Hole Oceanographic Institution     

Functional responses of juvenile herring and sprat in relation to different prey types

The relationship between particulate-feeding rates and prey concentrations (functional response) of juvenile herring and sprat (5–9 cm total length) was investigated in controlled feeding experiments monitored by an underwater camera system. A special tank system was developed allowing the regulation and quantification of low prey concentrations (1–160 L^?1). Non-evasive Artemia nauplii was used as prey to estimate the maximum biting rate of both predators. In contrast, Acartia tonsa with a high escape ability was used as a realistic prey type. Herring and sprat showed a type II functional response for both prey types. Nonlinear mixed effects model revealed no significant difference between the functional responses of both predators, except that herring showed significantly higher biting rates than sprat at A. tonsa concentrations below ~40 L^?1. For both predators feeding rates were significantly higher with Artemia nauplii than with A. tonsa. Video analysis indicated that sprat, unlike herring, is an obligate particulate-feeder.     

Filtering rates of the juvenile Atlantic menhaden Brevoortia tyrannus (Pisces: Clupeidae), with consideration of the effects of detritus and swimming speed

From July to September 1982 feeding experiments were conducted with 138-mm fork length Atlantic menhaden Brevoortia tyrannus (Latrobe) (Pisces: Clupeidae) to determine their particle size-specific feeding abilities. Monoculture clearing-rate experiments showed that the minimum size of particles filtered, the minimum size threshold, for 138-mm fish is 7 to 9 m. Filtration efficiency for three species of phytoplankton below the minimum size threshold. Pseudoisochrysis paradoxa, Monochrysis lutheri, and Isochrysis galbana, averaged 1.0% (n=14). Tetraselmis suecica, Prorocentrum minimum, and 2-celled Skeleionema costatum, phytoplankton which are larger than the minimum size threshold and smaller than the 20-m upper limit for nanoplankton, were filtered at efficiencies averaging 21% (n=24). S. costatum chains of 3 to 6 cells, prey particles exceeding the size limits of nanoplankton, were filtered at average efficiencies ranging from 22 to 84%. The mean filtration efficiency for Artemia sp. nauplii (San Francisco Bay Brand) of 36% (n=7) was lower than for smaller phytoplankton prey. The presence of detritus at concentrations usually encountered in nature enhanced filtering efficiency and lowered minimum size thresholds at which phytoplankton were retained. For small food particles, filtering efficiency decreased as swimming speed of the menhaden increased. As menhaden grow, their feeding tepertoire shifts to larger planktonic organisms.Contribution No. 1201 Virginia Institute of Marine Science     

Reanalysis of conversion efficiencies for larval Fundulus heteroclitus

The conversion efficiency (gross growth efficiency) of larval Fundulus heteroclitus fed newly hatched Artemia sp. nauplii was recently reported as the lowest observed (0.69 to 1.11%) for a fish. A recalculation of the efficiencies, based on data from Radtke and Dean, showed that the original determinations were in error by two orders of magnitude. The recalculated values (69.0 to 114.4%), however, are impossibly large and probably result from measurement error in the determination of the weight of a single prey individual (nauplius). Using a nauplius weight estimate from the literature, the conversion efficiencies were again recalculated. The new efficiencies (25 to 41%) agree with those reported for other fish species. The values are still higher than those reported elsewhere for adult F. heteroclitus, but this is consistent with the generalization that conversion efficiency decreases with age.Contribution No. 422 of the University of Georgia Marine Institute     

Effects of diet on fatty acid composition of body zones in larvae of the sea bass Dicentrarchus labrax: a chemometric study

Larvae of the sea bass Dicentrachus labrax were fed four Artemia sp. diets for 28 d. Three were nauplii enriched with emulsions of polyunsaturated fatty acids, and the fourth nauplii enriched with baker's yeast. At the end of the experimental period, the fatty acids of the bodies, heads and eyes of the larvae were analysed. A multivariate statistical method (discriminant analysis, DA) applied to the data revealed anatomical as well as dietary fatty acid pattern-discrimination. We propose here the use of discriminant analysis as a pattern-recognition method that will help to integrate the fatty acid information obtained in nutritional studies.     

Effects of feeding history on the growth characteristics of a reef fish at settlement

A feeding experiment was conducted on the pelagic stages of the tropical goatfish Upeneus tragula (family Mullidae) to examine how food quantity affects growth characteristics and potential success at settlement. Pelagic goatfish were collected from aggregation rafts 3 nautical miles west of Lizard Island on the northern Great Barrier Reef during December 1990. Three tanks in each of four feeding regimes were stocked with 25 pelagic goatfish between 20 and 23 mm standard length (SL). The four feeding regimes were: fed ad lib. (fed): fed once per day (f1pd); starved every second day (stld); starved for 3 d and re-fed (st3d). Fishes were fed 36 to 48 h old Artemia sp. nauplii (Ocean Star strain). Fish were removed from tanks when they underwent metamorphosis, changed pigmentation and settled to the bottom of the tanks. Morphology, muscle development, time taken to settle and biochemical condition were examined. Growth attributes of the treated fish were compared to fish which settled within 24 h of capture (field). All attributes examined were significantly influenced by the feeding treatments. Fish within the fed and st3d treatments were significantly larger and heavier than fish in the less well-fed treatments (f1pd, st1d). Similarly, concentrations of total lipid, carbohydrate and protein in the settled fish were significantly higher in the fed and st3d treatments compared with the st1d and f1pd treatments. For all these morphological and biochemical attributes the st1d and f1pd fish did not significantly differ from the field fishes, but did differ from the fed and st3d fishes. Water content was significantly higher in the f1pd, st1d and field fishes compared with the fed and st3d fish. Furthermore, the average time taken to settle followed the pattern: fed (14d)U. tragula are physiologically well suited to exploiting a patchy food source, and that food availability within the pelagic stages can have a major influence on the growth characteristics of this reef fish at settlement. The ramifications of this finding are discussed in relation to survival and success once fish have recruited to the reef population.     

Effects of prey escape ability,flow speed,and predator feeding mode on zooplankton capture by barnacles

Experimental studies of feeding on zooplankton often involve the use of non-evasive Artemia spp. to represent zooplanktonic prey. Some zooplankton, however, such as copepods, are potentially evasive due to possession of effective predator-avoidance mechanisms such as high-speed escape swimming. In the present study, we compared the efficiencies with which non-evasive (A. salina) and evasive (copepods) zooplankton were captured by a sessile, suspension feeder, the coral-inhabiting barnacle Nobia grandis (Crustacea, Cirripedia). N. grandis specimens and zooplankton used in the present study were collected near Eilat, Israel in 1993. The effect of different flow speeds (from 0 to 14 cm s^-1) on captures of the two preys was also investigated. Additionally, we examined the effect of a flow-induced barnacle behavioral switch from active to passive suspension feeding, on zooplankton capture. Two video cameras were used to make close-up, three dimensional recordings of predator-prey encounters in a computer-controlled flow tank. Frame-by-frame video analysis revealed a highly significant difference (P< 0.001) in the efficiency with which A. salina and copepods were caught (A. salina being much more readily captured than copepods). After an encounter with cirri of feeding barnacles, copepods were usually able to swim out of the barnacles capture zone within one video frame (40 ms), by accelerating from a slow swimming speed (approximately 1.85 cm s^-1) to a mean escape swimming speed of 18.11 cm s^-1 (ca. 360 body lengths s^-1). This was not the case for A. salina nauplii, which usually remained in contact with cirri before being transferred to the mouth and ingested. Thus, experimental studies addressing the methodology of organisms feeding on zooplankton should consider that slow-swimming prey like Artemia sp. nauplii may only represent the non-evasive fraction of natural mesozooplankton assemblages.     

Characteristics of feeding on dinoflagellates by newly hatched larval crabs

The zoeal larvae of brachyuran crabs must feed soon after hatching on a diet that includes large micro- and mesozooplankton in order to satisfy nutritional requirements. However, newly hatched larvae have been shown to ingest a variety of dinoflagellates, perhaps using microbial carbon sources to sustain them until they encounter more favored prey. Ingestion of dinoflagellates by larval crabs has been documented previously under conditions in which the larvae were exposed to algae provided in monoculture or in defined mixtures of cells. We report here on experiments conducted on the hatching stage of five crab species to determine if ingestion of dinoflagellates occurred when they were provided in combination with Artemia sp. nauplii or after a period of feeding on mesozooplankton. Quantitative measurements of chl a in the larval guts provided evidence of ingestion of algal cells. Active ingestion of the dinoflagellate Prorocentrum micans at specified intervals during an extended feeding period was determined on larvae of two crab species using fluorescently labeled cells provided for brief periods at prescribed time intervals. Stage 1 larvae of four of the five crab species ingested dinoflagellates when they were provided in combination with nauplii and larvae of all five species ingested cells after feeding solely on nauplii for 24 h. Ingestion of algal cells was first evident in the larval guts after 6 h of feeding at both low (200 cell ml⁻¹) and high (1,000 cells ml⁻¹) prey densities. Higher prey densities resulted in higher gut chl a. Larvae continuously exposed to dinoflagellates actively ingested cells at every 3 h interval tested over a 36 h period. Results confirm previous studies that larvae will ingest dinoflagellates even when they are encountered in a mixed prey field or when having previously fed. Ingestion of cells may occur on a continual basis over time.     

Predator shoaling moderates the confusion effect in blue-green chromis,Chromis viridis

Summary In experiments, blue-green chromis [Chromis viridis (Cuvier 1830)] were fed on either scattered or aggregated swarms of brine shrimp (Artemia sp.). Ten runs with each prey dispersion treatment were performed with shoals of one, two, five and ten chromis. The mean lag in reaching peak feeding rate for fish fed on aggregated prey was significantly shorter in the larger chromis shoals. In contrast, with the scattered treatment all such lags were similar and very short. As foraging proceeded, higher feeding rates were observed in the larger feeding shoals, regardless of prey dispersion. Prey capture success (i.e. the rate of retention of intercepted prey) declined with time, but was significantly higher in groups of ten fish. Two main conclusions emerge. Firstly, grouping facilitated initiation of feeding by individuals preying on concentrated swarms and reduced the delay in reaching a maximum feeding level. This may have been due to a suppression of the confusion effect through reduced reliance upon vigilance. Secondly, reduced vigilance allowed larger shoals of chromis to feed effectively over more extended periods. Trends of increasing shoal cohesion and decreasing prey retention rate with time were consistent with a postulated increase in antipredator vigilance with declining feeding motivation.     

Effects of dieldrin-contaminated food on the development of Leptodius floridanus larvae

Leptodius floridanus (Rathbun) (Decapoda: Xanthidae) larvae were fed dieldrin-contaminated Artemia nauplii throughout their development to megalopa. Sublethal effects were noted at dieldrin concentrations as low as 5.49 ppm, and no larvae completed their development when fed Artemia containing 33.0 ppm dieldrin. Organochloride pesticide residues were measured in zooplankton collected from Onslow Bay, North Carolina, USA. These residue levels were found to be much lower than those found to affect Leptodius larvae in the laboratory.     

Marker technique for investigating gut throughput rates in coral reef fishes

Artemia sp. shells were evaluated to determine their accuracy for tracing the passage of algal filaments through the gut of the damselfish Pomacentrus amboinensis Bleeker, 1868 (family Pomacentridae), an omnivorous coral reef fish. An automatic faeces-collection apparatus enabled the quantitative collection of markers and faeces in the laboratory. Defecation rates were similar for light and heavy doses of Artemia sp. shells and controls, indicating no detrimental effects of Artemia sp. shells on the gut throughput rate of P. amboinensis. In addition, similar rates and patterns of the passage of Artemia sp. shells and the algal markers Enteromorpha sp. and Lyngbya sp. indicated that Artemia sp. shells provide a reliable representation of the throughput rate of algal filaments. The mean throughput time of P. amboinensis was 4.6 h ±0.3 SE, with a modal recovery time of 4 h. Laboratory throughput estimates were validated by comparing the distribution patterns of Artemia sp. shells in the dissected gut of specimens administered markers in the laboratory and field. In addition, the retention of markers in the stomach of P. amboinensis suggested a likely site of prolonged processing. Received: 24 October 1996 / Accepted: 18 March 1997