Anchovy Engraulis Anchoita Research Articles

Contrasting distributional patterns of two co-occurring ctenophores in relation to ichthyoplankton and environmental features in the Southwestern Atlantic Ocean

Assessing the ecological role of ctenophores is crucial to understanding ecosystem functioning, including the recruitment of fish stocks. During austral summer in the North Patagonia Ecosystem (NPE) (41-48°S), the ctenophores Mnemiopsis leidyi and Pleurobrachia pileus co-occur with the peak of ichthyoplankton abundance of 2 important fishing resources: the Argentine anchovy Engraulis anchoita and the Argentine hake Merluccius hubbsi, in association with a highly productive tidal front system. We analyzed 367 plankton samples collected in the NPE over 13 yr (2005-2018) to determine the abundance and spatial distribution of M. leidyi and P. pileus, their spatial overlap with ichthyoplankton (eggs and larvae of hake and anchovy), and their relationship with environmental features. Both ctenophore species displayed contrasting distributional patterns, associated with different physical environments, particularly temperature. M. leidyi showed a higher spatial overlap with ichthyoplankton compared to P. pileus. In addition, we found a significant negative correlation between the biomass of M. leidyi and the abundance of both fish larvae, suggesting a potential negative impact (via predation and competition) on the survival and recruitment of these 2 fisheries resources.

Zonation of protistan plankton in a productive area of the Patagonian shelf: Potential implications for the anchovy distribution

In the southwestern Atlantic Shelf, in northern Patagonia, the coastal-inner shelf area of El Rincón (38°-41°S) is relevant due to retention processes and the occurrence of a mid-shelf front (MSF), which provide favorable habitat for the anchovy Engraulis anchoita, from which other commercial species feed on. Here, we assess the protistan plankton (>5 μm) composition and biomass during spring and summer of different years to explore the community structure at the base of the food web and its potential relation with the heterogenic spatial distribution of the anchovy's life stages previously reported in the literature. Our in situ data together with analyses of surface circulation patterns and satellite chlorophyll a denote a marked zonation of phytoplankton. We find that diatoms are the largest carbon contributors in the coastal sector and dinoflagellates near the MSF, where large copepods and mainly juveniles and adults of E. anchoita are found. In turn, transient small-scale eddies develop in the low chlorophyll central area dominated by nanoflagellates and ciliates, where small copepods and eggs and larvae of the anchovy dominate. Our results provide insights of the potential link between plankton assemblages, hydrological settings and developing stages of a highly exploited fish. Moreover, we contribute to biodiversity records used in global assessments of possible shifts at the population and community levels that might have cascading effects on marine ecosystems' productivity.

Marine fish imported from Argentina as source of human diphyllobothriosis in Europe? Ecological evidence from dolphins.

Diphyllobothriosis caused by the Pacific broad tapeworm Adenocephalus pacificus (syn. Diphyllobothrium pacificum) is an emerging parasitic disease reported also from non-endemic areas, including Europe (Spain). The origin of these human cases is unknown but should be related to fresh marine fish imported from endemic areas. In this study, we molecularly confirmed common dolphins Delphinus delphis off Argentina as euparatenic transit hosts of A. pacificus. Preliminary analysis of their stomach content, together with data from previous studies from the Southwest Atlantic, showed that common dolphins feed almost exclusively on schooling Argentine hake Merluccius hubbsi and Argentine anchovy Engraulis anchoita. Therefore, we suggest that Argentine hake and Argentine anchovy may represent the intermediate hosts of A. pacificus in the Southwest Atlantic, but also in Europe to where M. hubbsi is imported on ice (unfrozen).

Seabirds, environmental features and the Argentine anchovy Engraulis anchoita in the southwestern Atlantic Ocean

As top predators in marine environments, seabirds frequently respond to the presence of their main prey, and both predators and prey are usually associated with specific environmental features. We investigated the variability in the presence and density of flying seabirds (mostly Procellariiformes and Charadriiformes) and Magellanic penguinsSpheniscus magellanicusalong the southwestern (SW) Atlantic continental shelf. Five acoustic assessment surveys were conducted to determine the biomass of the Argentine anchovyEngraulis anchoita, and seabird counts and the collection of oceanographic data were conducted simultaneously with the surveys between June and October 2010. Generalized linear mixed models (GLMMs) were fitted to test the effect of anchovy density and environmental variables on seabird density. Sea surface temperature was significant for the presence of flying seabirds. Bottom water temperature and anchovy density were key variables affecting the presence and density of penguins, while bottom water salinity was also important for penguin presence. Based on Akaike’s information criterion, the most important factor explaining the density of flying seabirds was the difference between surface and bottom salinity (ΔS), while for penguin density, the most important factor was anchovy density. These results highlight that the subtropical shelf front in the SW Atlantic Ocean is a key feature influencing the aggregation of flying seabirds and confirm the close association of penguins and anchovies. Bottom water intrusion, originating from the sub-Antarctic shelf water, is an important factor explaining the presence of penguins, which tend to aggregate in areas with high anchovy densities on the SW Atlantic continental shelf.

Key prey indicates high resilience on marine soft bottom habitats

The key prey was determined based on the diet and spatial patterns of the Nektonic community in southern Brazil. The proposed tool to discriminate key prey was based on simple probabilistic methods and analytical procedures that integrate freely available software on the web. To avoid using arbitrary criteria in key prey determination it was used an indicator based on an adapted outlier analysis including a run of principal component analysis (PCA) and then the choice of prey that fall out of the 99% concentration ellipse. The results showed three key prey identified at species level: the shrimp Artemesia longinaris in the coastal habitats and euphausid Euphausia similis and anchovy Engraulis anchoita in the continental shelf habitats (warm and cold). The analysis of the diets of the indicator species of three necktonic assemblages showed that all of them had both pelagic and detritus as primary sources of energy. However, in shallow coastal waters prevailed access to benthic food web key prey. In deeper areas, the Warm shelf assemblage accessed more evenly the epifauna, infauna and the pelagic compartments, while the Cold shelf assemblage was more dependent on planktonic production and had a prevalence of pelagic key prey. Is demonstrated the importance of the identification of key prey, since it may indicate greater or lesser stability of predator populations depending on whether they come from compartments with more or less dynamic primary production processes, including climate-related changes that may affect the predator prey interactions. This study confirmed the prediction that demersal nekton has high disturbance recovery capacity, which may mask for decades the growing impact of fishing.

Energy Density Predictors for Argentine Anchovy Engraulis anchoita, a Key Species of the Southwestern Atlantic Ocean

AbstractForage fishes have a cosmopolitan distribution and constitute key species in marine trophic webs throughout the world. We estimated the energy density of the Argentine Anchovy Engraulis anchoita, a key component of the base of the food web in a large fraction of the southwestern Atlantic Ocean. We also examined the relationships between energy density and different proxies (condition factor, fork length, and percent dry weight) and compared the relationship of energy density to percent dry weight for Argentine Anchovy to this relationship in other forage fishes. A regression model that includes percent dry weight and fork length was the best predictor for the energy density in this species. The Argentine Anchovy had similar energy density to percent dry weight to all species in the Engraulidae family (anchovies) and to most of the species in the Clupeidae family (sardines). Engraulidae species showed smaller mean energy density and smaller energy density to percent dry weight compared with the Clupeidae species. The difference in energy density between these two families could have direct implications on population dynamics of predators in oscillating sardine–anchovy systems or in regions where these two families are spatially segregated.

Dinoflagellates Amyloodinium and Ichthyodinium (Dinophyceae), parasites of marine fishes in the South Atlantic Ocean.

The morphology and molecular phylogeny of the parasitic dinoflagellates Ichthyodinium chabelardi and Amyloodinium ocellatum was investigated off Brazil (South Atlantic Ocean). This is the first record of Ichthyodinium and the first molecular data of both parasites from the southern hemisphere. I. chabelardi infected the yolk of eggs of wild populations of Argentine anchovy Engraulis anchoita (Engraulidae) and Brazilian sardinella Sardinella brasiliensis (Clupeidae) in different seasons. The small subunit (SSU) rRNA and internal transcribed spacer (ITS) gene sequences were identical and confirmed Ichthyodinium as a host generalist. The new sequences clustered with the type species I. chabelardi from the North Atlantic and environmental sequences from the Pacific Ocean. A second species from the western Pacific remains undescribed. A. ocellatum was isolated from the gills of a cultured cobia Rachycentron canadum after causing mortality. The SSU rRNA gene sequence of the Brazilian isolate was almost identical to those from the northern hemisphere. This suggests a single species with a widespread distribution, although it is uncertain whether the species has a natural pantropical distribution or is the result of artificial distribution due to human-induced fish transport.

Blood-specific isotopic discrimination factors in the Magellanic penguin (Spheniscus magellanicus).

The use of stable isotopes for ecological studies has increased exponentially in recent years. Isotopic trophic studies are based on the assumption that animals are what they eat plus a discrimination factor. The discrimination factor is affected by many variables and can be determined empirically. The Magellanic penguin is a highly abundant marine bird that plays a key role in the southern oceans. This study provides the first estimation of the Magellanic penguin blood discrimination factor for (13) C and (15) N. A two and a half month feeding experiment was performed, in which ten captive penguins were fed their main natural prey (anchovy Engraulis anchoita). The discrimination factors were estimated by comparing anchovy δ(13) C and δ(15) N values (obtained with isotope ratio mass spectrometry using lipid-extracted and bulk anchovy muscle) with penguin blood δ(13) C and δ(15) N values. Penguin blood was shown to be enriched, compared with anchovies, for (13) C and (15) N. No changes were observed in the stable isotope ratios of anchovies and discrimination factors during the experiment. The overall discrimination factors were 0.93±0.12 (bulk) and 0.41±0.12 (lipid-free) for (13) C; and 2.81±0.17 (bulk) and 2.31±0.17 (lipid-free) for (15) N. Having an accurate discrimination factor for the studied species is key in any trophic or food web isotopic study. Comparisons of estimated diet-to-blood discrimination factors with published values of aquatic piscivore birds showed that the (13) C discrimination factor is particularly variable, and therefore ecologists should be cautious when using a surrogate value from other species. In this study, the Magellanic penguin discrimination factor of a tissue that does not require euthanasia was obtained, a fundamental input for trophic isotopic modeling of the species. Copyright © 2016 John Wiley & Sons, Ltd.

Trophic ecology of the smallnose fanskate Sympterygia bonapartii in the San Matías Gulf, northern Patagonia, Argentina

This study quantifies and describes the diet composition and variability, and the trophic ecology of Sympterygia bonapartii (Batoidea: Arhynchobatidae) in the San Matias Gulf, northern Patagonia, Argentina. A total of 1,047 stomachs were analyzed and 98 % of them contained food. The low proportion of empty stomachs recorded and the presence of prey in different stages of digestion suggested that this skate was a continuous feeder. A total of 81 prey items were identified. However, the diet was mainly composed of crabs. Other important groups in its diet were teleost fishes, shrimps and prawns, bivalves and worms. At the species level, the crab Peltarion spinosulum accounted for the highest contribution and the anchovy Engraulis anchoita ranked second in importance. By analyzing its diet composition, it was possible to classify S. bonapartii as a benthic predator, as are other skates reaching a similar maximum size. In addition, it was placed in the functional group of species that mainly feeds on decapod crustaceans. Trophic level was estimated at 3.61, indicating that the species was a secondary consumer. Significant differences were found in the diet according to sex, size class and season. These differences may be due to extrinsic and intrinsic factors that could be operating together.

Histological and histochemical study of the digestive system of the Argentine anchovy larvae (Engraulis anchoita) at different developmental stages of their ontogenetic development

AbstractIn this work, histological and histochemical features of the larval digestive system of Argentine anchovy Engraulis anchoita were described. Structural changes during ontogenetic development were also characterized, and comparisons between the beginning and the end of larval development were made. Histological sections of larvae were subjected to histochemical and routine histological techniques to localize and differentiate glycoproteins (GPs). Both at an early and a late larval stage, the oesophageal goblet cells reacted more intensely than those of the rest of the digestive tract, and only the oesophagus exhibited metachromasia with toluidine blue techniques at different pHs, thus revealing diverse GPs at different concentrations. The GPs histochemical composition in the intestine varied with the developmental stage and the intestinal zone. The absence of goblet cells characterized the foregut; however, they started differentiation at an advanced stage in the midgut. These cells could be detected in the hindgut both at the beginning and at the end of development. The attached glands showed a varied glycoprotein composition. The digestive tract of E. anchoita presented a high level of complexity, related to the multiple functions of mucus in the digestive tract, such as lubrication, protection, antimicrobial function and ionic and osmotic regulation.

Molecular identification and larval morphological description of Contracaecum pelagicum (Nematoda: Anisakidae) from the anchovy Engraulis anchoita (Engraulidae) and fish-eating birds from the Argentine North Patagonian Sea

Anisakids use invertebrates as paratenic and/or intermediate hosts as a basic feature of larval transmission. The third-stage larva usually develops in invertebrates which are prey items of finfish paratenic hosts. Contracaecum larvae molt twice inside the egg and hatch as free third-stage larvae ensheathed in the second-stage larval cuticle. Copepods act as paratenic or obligatory hosts, usually ingesting these free L3 larvae, and fish act as intermediate/paratenic or metaparatenic hosts preying on infected copepods. Fish-eating birds acquire L3 larvae by ingesting infected fish where they develop into the fourth-stage larvae and adults. Objectives of this work were to establish the specific correspondence between Contracaecum pelagicum L3 larvae parasitizing the anchovy Engraulis anchoita, and the adults parasitizing the Magellanic penguin Spheniscus magellanicus and the Imperial shag Phalacrocorax atriceps through the use of molecular markers; and, to evaluate the anisakid L3 larval recruitment and infection caused by ingestion of anchovy by S. magellanicus. Sixteen specimens of Contracaecum L3 larvae were analyzed from E. anchoita from Bahía Engaño, Chubut, eight adult nematodes from S. magellanicus and six adult specimens from P. atriceps both from the Valdés Peninsula, Chubut. All nematodes were sequenced for three genes: mitochondrial cytochrome oxidase 2 (mtDNA cox2), mitochondrial ribosomal RNA (rrnS), and the internal transcribed spacers (ITS-1 and ITS-2) of the nuclear ribosomal DNA region. Phylogenetic analyses were performed by using Maximum Parsimony (MP) analysis by PAUP. In addition, studies under SEM and LM were carried out on L3 larvae. All L3 individuals from E. anchoita, adults from S. magellanicus, and P. atriceps clustered in the same clade, well supported in the MP tree inferred from the mtDNA cox2, and rrnS gene sequences analyses. Further, the sequence alignments of L3 larvae and adults of C. pelagicum here obtained at the ITS-1 and ITS-2 regions of the rDNA matched the sequences of C. pelagicum previously deposited by us in GenBank. Nematode recruitment (Ro) was equal to 33.07 (7.20–91.14) L3 larvae for C. pelagicum in each penguin's meal of anchovy. The MP tree topologies obtained from mtDNA cox2 and rrnS genes demonstrated that specimens of Contracaecum L3 larvae from E. anchoita and C. pelagicum from S. magellanicus as well as from P. atriceps constitute a unique clade, well-distinct and supported from all the others formed by the Contracaecum spp. sequenced so far for these genes. Molecular markers are considered to be an effective tool to elucidate larval transmission. The Contracaecum L3 larval recruitment value showed that many worms fail to establish in the bird digestive tract, probably because they are below a critical size. Further work is needed to elucidate other factors (e.g., physiological, immunological) that control nematode populations in the penguin digestive tract.

Reproductive success of the Argentine anchovy, Engraulis anchoita, in relation to environmental variability at a mid‐shelf front (Southwestern Atlantic Ocean)

AbstractThe mid‐shelf front (MSF) of the Buenos Aires province continental shelf in the Southwestern Atlantic Ocean plays a central role in the pelagic ecosystem of the region acting as the main spring reproductive area for the northern population of the Argentine anchovy Engraulis anchoita and supporting high concentrations of chlorophyll as well as zooplankton, the main food of anchovy. To investigate the influence of environmental variability on the reproductive success of E. anchoita, we analyzed a 13‐yr time series (1997–2009) of environmental data at MSF including chlorophyll dynamics, as well as zooplankton composition and abundance, ichthyoplankton distributions, and recruitment of E. anchoita. Spring chlorophyll concentrations showed high interannual variability and were mainly influenced by changes in water temperature and vertical stratification, which in turn control nutrient supply to the surface. Chlorophyll dynamics (magnitude, timing, and duration of the spring bloom) explained most of the variability observed in E. anchoita recruitment, most likely via fluctuations in the availability of adequate food for the larvae. Our results suggest that satellite ocean color products can be valuable tools for understanding variability in ecosystem dynamics and its effects on the recruitment of fish.

Nutritional condition of Argentine anchovy Engraulis anchoita larvae in connection with nursery ground properties

Nutritional condition of anchovy Engraulis anchoita larvae from Northern Argentinean sea was assessed and compared in three areas characterized by dissimilar oceanographic features (estuarine, mixed and shelf waters). Morphometrical, histological and biochemical (RNA/DNA) indexes were used and larvae were compared through different developmental stages. Multivariate analyses performed on normalized morphometric variables showed that larvae from mixed waters where characterized by higher body depths; variables that indicate a better nutritional condition. Mean histological condition index obtained for larvae at intermediate developmental stages was significantly lower in estuarine waters than those estimated with samples from mixed or shelf waters. Anchovy larvae from the mixed water area showed a higher slope in the log RNA versus log DNA relationship than larvae from the other areas, which indicates that the former were in better condition. Also, standardized RNA/DNA index (RNA/DNA s) resulted slightly better in mixed waters than in shelf area, for larvae at intermediate developmental stages, but due to the high variability of RNA/DNA ratio, no significant differences were found between areas. Finally, using literature equations relating RNA/DNA s, temperature and growth, growth rate and growth performance were estimated. Mean growth performance did not differ between areas and was temperature independent. In conclusion, larval condition was relatively high at all stations, but our results suggested that it was slightly better in frontal areas characterized by water masses with intermediate salinities. We also provide evidence that anchovy larvae might not be food limited in any of the studied areas.

Diet and feeding of the cutlassfish trichiurus lepturus in the subtropical convergence ecosystem of southern brazil

the diet and feeding of the cutlassfish trichiurus lepturus were studied based on analyses of the stomach contents of larvae, juveniles, and adults collected along the continental shelf and shelf break off southern brazil, from the cape of santa marta grande (28°36′s) to chuí (34°45′s). the larvae and pre-juveniles with a total length of <5 cm were found to have fed almost exclusively on calanoid copepods, whereas juveniles (5 to 30 cm) fed on small zooplanktonic crustaceans such as lucifer faxoni and promysys atlantica. on the other hand, sub-adults (30 to 70 cm), fed on euphausiids, mainly euphausia similis, and small fish, mostly anchovy engraulis anchoita. adults (70 to 160 cm) fed on a wide range of larger prey, such as anchovy, sciaenid fish, cephalopods and coastal shrimps, as well as euphausiids. the juveniles and sub-adults fed more intensively than adults during the warm-water season whereas adults fed more intensively during the cold-water season. feeding activity was more intense at night, while cannibalism was more frequent during the warm season, when biological productivity was lower. finally, diet diversity was higher in coastal waters, during the warm season. the abundance of cutlassfish off southern brazil may be explained by the fact that it is adapted to feed on a wide size-range of both pelagic and demersal prey.

Appendicularians: an important food supply for the Argentine anchovy Engraulis anchoita in coastal waters

Summary The stomach contents of 532 adult specimens of the Argentine anchovy, Engraulis anchoita, caught in coastal waters of the Argentine Sea from 1994 to 1996, were analyzed. Larger amounts of food were found in the stomachs of anchovies collected in the northern surveys (35–40°S), with the highest values attained in 1994. Main diet items were copepods, appendicularians, cladocerans, fish eggs, and pteropods. Anchovies caught in the southern surveys (40–45°S) ingested less food, whereby the main items were copepods and appendicularians. Plankton samples collected simultaneously with the fishing trawls were also analyzed. Except for Fritillaria borealis, which occurred only in plankton samples, the same appendicularian species (Oikopleura dioica and O. fusiformis) were found in both stomach contents and in plankton samples. The Ivlev selectivity index calculated for O. dioica and O. fusiformis and for the different maturity stages of both species were in all cases ∼0, supporting the hypothesis of a non-selective feeding.

HOW DO MAGELLANIC PENGUINS COPE WITH VARIABILITY IN THEIR ACCESS TO PREY?

Movements of animals provisioning offspring by central place foraging extend from short, highly local trips where food is brought back essentially unchanged from its normal condition to extensive interseasonal movement where the offspring are nourished from body reserves built up during the adult's absence from the breeding site. Here, appropriate strategies for maximizing lifetime reproductive success depend on the abundance and location of prey in relation to breeding sites and the energetics and speed of travel of the animal. Magellanic PenguinsSpheniscus magellanicusundertake central place movements that are particularly variable during the incubation period; trips may last from a single day to over three weeks depending on colony locality. We reasoned that site‐specific variability in prey distribution and abundance is responsible for this. Remote‐sensing systems attached to 92 penguins from six different colonies over the species distributional range over the Patagonian Shelf were used to determine space use and foraging patterns in an attempt to understand the observed patterns. Birds in the north and south of the latitudinal range were essentially monophagic, feeding primarily on anchoviesEngraulis anchoitaand spratsSprattus fuegensis, respectively, both species that are to be found relatively close to the colonies. Penguins in the center of the distributional range, where these pelagic school fish prey are essentially absent at that time of the year, traveled either north or south, to the same regions utilized by their conspecifics, presumably to exploit the same prey. A simple model is used to clarify patterns and can be used to predict which movement strategy is likely to be best according to colony location. During chick rearing, southerly movement of anchovies and northerly movement of sprats mean that Magellanic Penguins in the center of the distributional range may benefit, although the abundance of these fish is considered to be less than that closer to the Magellanic Penguin range limits. The extensive time involved in the foraging trips during incubation coupled with the postulated poorer prey conditions during the chick‐rearing phase may help explain why Magellanic Penguin colony sizes in the center of the range are not elevated.

Feeding habits of the juvenile striped weakfish, Cynoscion guatucupa Cuvier 1830, in Bahía Blanca estuary (Argentina): seasonal and ontogenetic changes

The aim of this study was to analyze the feeding habits of the juvenile striped weakfish, Cynoscion guatucupa Cuvier, from Bahia Blanca estuary, Argentina. C. guatucupa is one of the most important regional fishing resources although in the last 10 years landings have greatly decreased. The year class strength of fish as well as stock size and yield are determined during the early life stages. Knowledge about the diet of young C. guatucupa may therefore contribute to our better understanding of the influence that the changes occurring in the biota of the estuary exert on the abundance fluctuations of this species. To this end, we investigated the ontogenetic and seasonal dietary changes of C. guatucupa between 1.00 and 12.99 cm total length (age 0+), and we related them to changes in habitat use and prey selection. Two dietary shifts were found during ontogeny. The first shift, at approximately 4 cm total length, involved a change from demersal-pelagic prey (mysid shrimps) to demersal-benthic prey (Peisos petrunkevitchi Burkenroad). The second shift, at approximately 8 cm total length, involved a progressive increase in ichthyophagy (mainly an increase consumption of the Argentine anchovy Engraulis anchoita Hubbs & Marini). Seasonal dietary changes were also found. They evidenced the changes in the availability of organisms. In autumn, the chaetognath Sagitta friderici Ritter-Zahoni, P. petrunkevitchi, and E. anchoita were the dominant prey items; in winter, the copepod Labidocera fluviatilis Dahl along with S. friderici, mysids, and P. petrunkevitchi constituted the majority of the diet; and, in summer, mysids were the most important prey item consumed. Selectivity data showed that whereas some prey items, such as the copepods Acartia tonsa Dana and Paracalanus parvus (Claus) and S. friderici, were consistently negatively selected by all size classes throughout the year, other prey items, such as fish larvae, mysids, and P. petrunkevitchi,were selected in one season and avoided in another. Additional dietary seasonal differences observed in our research indicate that the limited food supply and the low water temperatures are limiting factors for winter juveniles in BahOa Blanca estuary. These factors may also directly influence the more-than-10 cm total length seaward migration of large numbers of C. guatucupa that is registered at the end of every autumn.

Morphological and histochemical characterization of the mucosa of the digestive tract in Engraulis anchoita.

The histomorphological aspects as well as the histochemical content and distribution of glycoproteins (GPs) in the mucosa of the digestive tract of the anchovy Engraulis anchoita were studied. The buccopharyngeal cavity is lined by a squamous stratified epithelium with mucous superficial cells; the oesophagus shows two zones, cranial with a squamous stratified epithelium with mucous superficial cells and caudal with a columnar secretory epithelium. Finally, the stomach presents both the cranial and pyloric portion lined with a simple columnar epithelium. Tubular branched glands, formed by a single type of glandular cell, located along the stomach, are more numerous in the cranial portion. The GPs were identified with (1) oxidizable vicinal diols; (2) sialic acids and some of their chain variants, C7 or C9; (3) sialic acid residues with O-acyl substitution at C7 or C8; (4) carboxyl groups and (5) sulphate groups. Histochemical tests showed that the buccopharyngeal cavity presented the largest amount of the different types of mucosubstances. Epithelial secretory cells were found in the oesophagus, which synthesized a large quantity of sialosulphoglycoproteins likely to be related to a protective role. The surface epithelium of the stomach synthesizes and secretes acid and neutral GPs, probably related to the movement of fluids and to the absorption of easily digested substrates, respectively. Although great differences exist between different species, in E. anchoita as in other fish species, the wall of the digestive tract is composed of the four layers classically described for vertebrates. The GPs secreted by the epithelial cells are suggested to be important for the protection and inhibition of microorganisms. In addition, they are involved in enzymatic digestion of food, absorptive functions and lubrication of the alimentary tract.

Parasites of Argentine anchovy in the south‐west Atlantic: latitudinal patterns and their use for discrimination of host populations

Four stocks of Argentine anchovy Engraulis anchoita in the south‐west Atlantic, south of 34°S were identified by the use of parasites as biological tags. A total of 671 fish were examined for parasites and 19 parasite species were found in 664 Argentine anchovies. The parasite populations and both infra‐ and component communities showed marked latitudinal gradients. Cluster analyses allowed the identification of four groups, one composed of autumn samples (35–37°S) and three of spring ones. Among the latter, a Patagonian group (43–46°S) was clearly separated from a Bonaerense group, which was divided into two groups: North Bonaerense (34–40°S) and South Bonaerense (40–43°S). Autumn samples were characterized by low values of prevalence for most parasite species. Among spring samples Pseudanthocotyloides heterocotyle, Lecithochirium microstomum, Parahemiurus merus, Scolex polymorphus and Corynosoma australe were characteristic of the northern region, whereas Cardiocephaloides sp., Anisakis simplex, Contracaecum sp. and Hysterothylacium aduncum were more prevalent in southern waters. Latitudinal environmental gradients and their influence on the distribution of both zooplankton and definitive hosts, could be determinants of the clines observed.

Environmental patterns and biomass distribution of gelatinous macrozooplankton. Three study cases in the South-western Atlantic Ocean

Fil: Mianzan, Hermes Walter. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigacion y Desarrollo Pesquero; Argentina