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.     

Metazoan parasites of Sebastes capensis from two localities in northern Chile as tools for stock identification

Examination of 290 red rockfish Sebastes capensis from two fishing grounds in northern Chile (Coquimbo 71°30' W; 30°0' S and Antofagasta 70°40' W; 23°30' S) revealed 8770 metazoan parasites, belonging to 18 taxa: Udonella caligorum (Udonellidae); Interniloculus chilensis , Paramicrocotyle sp. and Neobenedenia melleni (Monogenea); larval Gnathia sp., Cirolana sp. and Rocinela sp. (Isopoda); Helicometrina nimia , Diphtherostomum sp., Lecithochirium sp. and Pseudopecoelus sp. (Digenea); Ascarophis sebastodis , Anisakis sp. and larval Hysterothylacium sp. (Nematoda); Caligus cheilodactylus , Lepeophtheirus chilensis and Trifur tortuosus (Copepoda); larval Corynosoma australe (Acanthocephala). Ten species were found only in Coquimbo and three were found only in Antofagasta, species common to both localities were Pseudopecoelus sp., C. australe , Anisakis sp. and A. sebastodis . Evidence, based on qualitative differences between the parasite faunas of the red rockfish, suggests the existence of two discrete stocks.     

A new species of Paracapillaria (Nematoda: Capillariidae) parasitizing the Brazilian sandperch, Pinguipes brasilianus (Pisces: Pinguipedidae), from Argentina

A new species, Paracapillaria argentinensis n. sp., is described from the pinguipedid fish Pinguipes brasilianus Cuvier, 1829 from waters off Mar del Plata, Argentina (38 degrees 08'S, 57 degrees 32'W) (prevalence 22.2%; mean intensity +/- SD, 4.42 +/- 5.19). The new species is assigned to the subgenus Paracapillaria Moravec, 1987. Of the 10 species so far known in the subgenus, the new species more closely resembles P. (P.) plectroplites, from which it is distinguished by having a spicule with an expanded anterior end and a slender medial section. A similar spicular morphology is observed in P. (P.) epinephell; however, it shows shorter spicules and a highly reduced caudal bursa. This is the first record of Paracapillaria in the southwestern Atlantic Ocean.     

Metazoan parasites of the thumb grenadier Nezumia pulchella, from the south-eastern Pacific, off Chile, and their use for discrimination of host populations

The parasite communities of Nezumia pulchella across its geographical range in the south-eastern Pacific were described, from 217 fish captured from four localities in northern and central Chile (24° S to 33° S). Five ectoparasites and 13 endoparasites were recorded and the highest prevalence and intensity of infection was found for the copepods Jusheyhoea macrura and Clavella sp. 1, for the monogenean Diclidophora sp. and for the larval acanthocephalan Corynosoma australe . Parasite species richness decreased with latitude. Multivariate discriminant analysis and correspondence analysis supported the use of parasites of N. pulchella to discriminate populations of this host, suggesting the existence of three well-defined host populations in the geographical range examined. Jusheyhoea macrura , C. australe , Lophoura sp., Diclidophora sp., Capillaria sp. and Proleptus sp. were the most important species for discriminant analysis.     

Parasites of Cynoscion guatucupa along South American Atlantic coasts: evidence for stock discrimination

Two stocks of striped weakfish Cynoscion guatucupa in the south‐west Atlantic Ocean, were identified using parasites as biological tags. A total of 297 fish caught in Brazil, Uruguay and Argentina, contained 29 species of metazoan parasites. Univariate analysis on parasite populations, as well as multivariate discriminant analysis, calculated for juvenile and adult fish separately, allowed the identification of the two stocks, one from Argentina and Uruguay and the other from Brazil, to be made. Southern samples were characterized by higher prevalences and abundance of larval endohelminths, whereas in the northern stock, gastrointestinal and ectoparasitic species were common. Discriminant analyses on parasite infracommunities of Brazilian fish showed notable differences between juvenile and adult hosts; no such trend was observed in fish from Argentina and Uruguay, despite differences between juveniles and adults at the population level. Different oceanographic conditions and their influence on the distribution of parasites as well as of other hosts involved in their life cycles could be key factors for the differences observed among stocks of C. guatucupa .     

Genetic identification of Anisakis larvae in European hake from Atlantic and Mediterranean waters for stock recognition

The occurrence of seven species of the larval parasitic nematode Anisakis , which can be used as a biological tag for hake Merluccius merluccius stocks throughout their geographical range, is reported. Hake were collected from 14 localities in the Mediterranean Sea and the Atlantic Ocean. Anisakis larvae ( n  = 1950), which were recovered, were identified to species by means of genetic markers (allozymes). Within Anisakis type I, the larvae of A. pegreffii , A. simplex s.s ., A. typica and A. ziphidarum were detected, while within Anisakis type II, A. physeteris , A. brevispiculata and Anisakis sp. were identified. There were significant differences in the relative proportions of the various Anisakis species identified in hake samples from the Mediterranean Sea and Atlantic Ocean, suggesting the existence of different stocks of M. merluccius in European waters.     

Introductions, spread and colonization of new localities by fish helminth and crustacean parasites in the British Isles: a perspective and appraisal

Most parasites are disseminated by movements of infected hosts. The increasing extent and rapidity of anthropochore fish movements are causing increased concern related to awareness of their potential and known capacity for disseminating parasites. This paper puts these data in perspective by examining examples of actual and potential translocations of fish helminthes and crustaceans by anthropochore movements offish into and throughout the British Isles, and by distinguishing the processes of dissemination and invasiveness from those of colonization and establishment. An investigation of the British fish and helminth parasite fauna suggests that: (1) the range of many species is not well known, many are local in distribution and appearances beyond the range may reflect detection and patchiness, not translocation; (2) taxonomic problems in many groups hinder detection and determination of range; (3) most parasites possess the attributes of good colonizers so the natural expansion and contraction of ranges are often not noticed or recognized as such and the importance of parasite introductions by natural movements of fish or avian hosts is generally underestimated; (4) invasions are far commoner than colonizations, since conditions for establishment may be very restricted and transmission windows very narrow in time and space; (5) successful colonizations and translocations tend to be documented and attract attention whereas invasions resulting in failed colonizations are seldom observed and more seldom documented, thus biasing our perception. Given the extensive history of fish introductions to, and translocations within, the British Isles it is surprising how few fish helminths and crustaceans have invaded the country successfully (16 species: 11·4%) and how many still show restricted distributions. The majority (68·7%) of introduced helminths are associated with fish having ornamental varieties. Barriers of colonization are more effective than those to invasion and it is clear that most translocations and invasions fail. It is right to be concerned about the dangers, but it is also important to put anthropochore factors in perspective.     

Anterior adhesive areas and adjacent secretions in the parasitic flatworms Decacotyle lymmae and D. tetrakordyle (Monogenea: Monocotylidae) from the gills of stingrays

Abstract. The monogeneans Decacotyle lymmae and D. tetrakordyle (Monocotylidae: Decacotylinae), from gills of the dasyatid stingrays Taeniura lymma and Pastinachus sephen , respectively, have a single aperture for adhesive secretion on each side of the anterior ventrolateral region. Rod-shaped bodies (S1) and electron-dense spherical secretion (S2) exit through specialised ducts opening adjacent to one another within these apertures. The S1 bodies are 230 ± 11 nm wide and ≥4 μm long in D. lymmae and 240 ± 9 nm wide and ≥3.3 μm long in D. tetrakordyle . The S2 bodies have a diameter of 88 ± 7 nm in D. lymmae and 65 ± 6 nm in D. tetrakordyle . The apertures are unusual in being extremely small (internal diameter, 3–5 μm). Each aperture has a slit-like surface opening as small as 160 nm wide, surrounded by muscle fibres indicating that they may be opened and closed. The aperture is also surrounded and underlain by muscle fibres that may aid in secretion from, or even eversion of, the tissue within the aperture. Sensilla/cilia are also found within the apertures. Additional secretions from anteromedian and anterolateral glands (body glands), each containing granular secretions, occur in profusion and exit anteriorly and posteriorly to the position of the apertures, through duct openings in the general body tegument. These granular secretions do not appear to be associated with anterior adhesion. Both species show similarities in aperture, underlying tissue, sense organ, and secretion detail, in accordance with findings from other monogenean genera, and which supports the importance of such data for phylogenetic studies.     

Spatial variation in parasite abundance: evidence of geographical population structuring in southern garfish Hyporhamphus melanochir

Southern garfish Hyporhamphus melanochir were examined for metazoan parasites from nine sites in three regions (Spencer Gulf, Gulf St Vincent and northern Kangaroo Island) in South Australia to document parasite assemblages, identify candidate species suitable for use as biological tags and investigate spatial variation in parasite abundance. Four ectoparasite and 10 endoparasite species were identified representing Cestoda, Trematoda, Monogenea, Nematoda, Acanthocephala, Copepoda and Isopoda. Lernaeenicus hemirhamphi, Micracanthorhynchina hemirhamphi, Mothocya halei and Philometra sp. were suggested for 'permanent' biological markers. Multivariate discriminant function analysis showed that most sites could be distinguished based on differences in parasite abundance. Four endoparasites (Conohelmins sp., Hysterothylacium sp., M. hemirhamphi and Philometra sp.) were most important for site characterization. Limited spatial variation in permanent endoparasite abundance among localities in northern Spencer Gulf provided evidence for a distinct northern Spencer Gulf population with little interregional mixing. In contrast, considerable spatial variation in permanent endoparasite abundance between localities sampled off Kangaroo Island implied limited local movement and suggested H. melanochir may comprise a metapopulation structure. These results largely align with recent evidence from otolith chemistry that indicates fine-scale geographical population structuring in South Australian waters.     

Populations and assemblages of parasites in hake, Merluccius gayi, from the southeastern Pacific Ocean: stock implications

To assess fish stocks, the populations and community assemblages of metazoan parasites were compared in 1172 Chilean hake Merluccius gayi landed at two major ports, and caught during 1991–1992 in three major fishing areas off central Chile. At least two ecological stocks are suggested, based on consistent differences in parasitism between body length classes for Grillotia dollfusi, Hysterothylacium sp., Clestobothrium crassiceps and Aporocotyle wilhelmi . More use should be made of the information on whole parasite assemblages including, for example, patterns of co-occurrence of parasite species. Univariate analyses on selected taxa in samples from different areas may show no differences because of the same prevalence or abundance for each parasite taxon, but opposite numerical arrangements of co-occurring taxa in community assemblages would remain undetected.     

Seasonal variability of inorganic and organic nitrogen in the North Sea

This study considers the cycling of nitrogen in the waters of the North Sea, particularly focussing on organic nitrogen. Dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and particulate organic nitrogen (PON) were measured in the North Sea over a one-year period (autumn 2004–summer 2005). The surface water concentrations of nitrate, ammonium, DON and PON during the present study ranged from <0.1–7.2 μM, <0.1–2.0 μM, 1.9–11.2 μM and 0.3–5.6 μM, respectively, with DON the dominant fraction of total nitrogen at all times. These nutrients concentrations were significantly lower compared to previous studies in the southern North Sea. The seasonal variations showed high mean surface concentrations of nitrate (4.7 ± 0.6 μM) and DON (8.9 ± 0.9 μM), low ammonium (<0.1 μM) and PON (0.8 ± 0.1 μM) in winter, shifting to low nitrate (0.3 ± 0.3 μM) and DON (4.2 ± 1.2 μM) in summer, with high ammonium (0.8 ± 0.4 μM) in autumn and PON (2.5 ± 1.2 μM) in spring. Highest mean surface DON concentration was measured in winter and may be due to resuspension of the organic matter from the bottom sediments. For autumn and spring, phytoplankton DON release was likely to be the most significant source of DON as shown by high concentrations of low molecular weight (LMW) DON and its positive correlation to chlorophyll a. Low total and LMW DON concentrations during summer were likely to be due to the uptake of the LMW DON fraction by phytoplankton and bacteria and the stratification of the water column. DON is therefore shown to be a potentially important source of nitrogen in shelf seas especially after the spring bloom has depleted nitrate to limiting concentrations. Handling editor: L. Naselli-Flores     

Morphological variability of the shape of striped red mullet Mullus surmuletus in relation to stock discrimination between the Bay of Biscay and the eastern English Channel

Truss analysis and length measurements were made on 168 striped red mullet Mullus surmuletus. Multivariate statistical analyses with principal component analysis and partial redundancy analysis (pRDA) were used on these measurements to evaluate the influence of maturity, sex and geographical area distribution on body shape. Truss measurements were important to quantify and discriminate changing body shape, presumably due to changing environmental conditions. Sexual dimorphism was not observed and juveniles could be distinguished from adults based on their body shape. More importantly, M. surmuletus occurring in different geographical areas could be differentiated using this method. Based on pRDA, a significant difference of head morphological dimensions was observed between populations occurring in the eastern English Channel and those occurring in the Bay of Biscay, suggesting that fish from these areas could represent two subpopulations.     

Parasites as biological tags for stock discrimination of the Brazilian flathead Percophis brasiliensis in the south-west Atlantic

Three stocks of the Brazilian flathead Percophis brasiliensis were identified on the coast of Argentina and Uruguay using parasites as biological tags. A total of 177 fish were examined and 23 parasite species were found. Fish were caught in four zones: north of the Argentine–Uruguayan Common Fishing Zone (34°30′–36°30′ S; 53°30′–56°00′ W), south of the Argentine–Uruguayan Common Fishing Zone (38°08′ S 57°32′ W), El Rincón zone (39–41° S; 60–62° W) and San Matías Gulf (41°40′–42°10′ S; 63°50′–65°00′ W). Discriminant analyses allowed the identification of three discrete stocks in the four zones (86·44% of classified samples were correctly identified), with P. brasiliensis from both north and south of the Argentine–Uruguayan Common Fishing Zone clumping together, as a single stock. Some species were important in discriminating among groups, Anisakis simplex was related to southern areas, while Grillotia sp., Corynosoma australe and Hysterothylacium sp. were important in determining the position of fish from the Argentine–Uruguayan Common Fishing Zone. These results were corroborated by comparing parasite prevalence and abundance among zones. The main differences were observed in those comparisons involving fish from the San Matías Gulf. Fish from the Argentine–Uruguayan Common Fishing Zone were characterized by higher infections of Grillotia sp., C. australe, Corynosoma cetaceum and Hysterothylacium sp., while the samples from El Rincón and San Matías Gulf showed higher infections of A. simplex. Samples from San Matías Gulf were characterized by lower levels of parasitism for all other species. Differences in environmental factors and their influence on the distribution of zooplankton and other hosts in the food web may be differentially shaping the parasite community structure in each zone, resulting in identifiable stocks of the P. brasiliensis. The present study confirmed the existence of regional biological tags that delineated fish assemblages.     

Local variability in metazoan parasites of the pelagic fish species, Engraulis ringens: implications for fish stock assessment using parasites as biological tags

Parasites have been used successfully as biological tags in population studies, mainly in marine fishes, but also in marine mammals, crustaceans and molluscs. Almost all published information dealing with parasites as biological tags evaluates differences between localities. However, local variability in the component community has not been assessed. In this work, we examined whether local variation of the metazoan parasite fauna of Engraulis ringens, extracted from five independent samples from two nearby localities in northern Chile, can be a factor causing bias in stock identification. Our results show that local variability, as estimated by a single sample, may suffice to represent component community variability with no need for replicated data.     

Habitat-related differences in the abundance of parasites from a coral reef fish: an indication of the movement patterns of Hemigymnus melapterus

The prevalence and number of an undescribed Benedenia sp. on Hemigymnus melapterus were significantly greater on fish from the reef flat than from the slope at Heron Island, Great Barrier Reef. In contrast, the abundance of gnathiid isopods on the fish did not differ significantly between habitats. As monogeneans do not leave their hosts, the differences in parasite abundance between the habitats suggest that H. melapterus does not move between the reef flat and reef slope, habitats separated by only a few hundreds of metres. Benedenia may thus be a useful biological tag for following the small-scale movement patterns of coral reef fish.     

Temporal and spatial variability of pelagic wild fish assemblages around Atlantic bluefin tuna Thunnus thynnus farms in the eastern Adriatic Sea

The abundance and size structure of wild fishes aggregated around the sea‐cages of two commercial Thunnus thynnus farms, including control locations, were assessed and compared over a 1 year period. The T. thynnus farms were located in the eastern Adriatic Sea, offshore of the islands of Ugljan and Bra?. Fish assemblages were evaluated through visual census using scuba at 2 month intervals at two sites within each farm. The data suggest that wild fish assemblages at the study sites differed greatly; 20 species occurred at the Ugljan farm and 17 at the Bra? farm, while only seven species were observed at the control locations. The abundance and diversity of wild fish assemblages were greater at the farms in comparison to control locations. The most abundant families were Sparidae and Belonidae (>80% of aggregated fishes). At both farms, the abundance and diversity of wild fishes were highest during summer, while diversity was lowest in winter and was mainly characterized by schools of bogue Boops boops and garfish Belone belone. Variability was also detected in spatial assemblages between farms; B. boops and B. belone were the most abundant species for the overall study at the Bra? farm, while B. belone and saddled bream Oblada melanura were the most abundant at the Ugljan farm. The settlement also played a significant role in farm‐associated fish assemblages, as both juveniles and advanced juveniles were common residents at farms. The majority of species which settled at the farms belonged to the sparids. Results indicate that aggregations of wild fishes at T. thynnus farms are persistent year‐round, though the assemblage compositions and size structures of dominant species vary in respect to location and season.     

Seasonal variation in the composition of fish assemblages in small Amazonian forest streams: evidence for predictable changes

1. The effects of seasonal inundation on the biology of fishes on floodplains of large Amazonian rivers are well studied. However, the small seasonal changes in headwater streams are generally considered to have little effect on fish assemblages. 2. In this study, we analysed seasonal changes in the species composition and abundance of fish in small Amazonian forest streams. We sampled fish with hand and seine nets in headwater streams in a 10 000 ha terra‐firme forest reserve near Manaus, Brazil. Each stream was surveyed at the end of the 2005 dry season, at the beginning of the 2006 rainy season and at the beginning of the 2006 dry season, by means of a standardized sampling effort. 3. The numbers of individuals and species caught were higher in the dry season, but rarefaction analyses indicated that greater species numbers could have been due simply to the larger number of individuals caught. 4. Between the dry and rainy season, the direction of changes in species composition in multivariate space varied among sites, especially for quantitative (abundance) data. However, the observed variation among sites was the less than expected if the directions of change were random. 5. Fish assemblages in the second dry season were more similar to those in the previous dry season than expected if changes in species composition among seasons were random. This indicates that a general seasonal pattern in fish assemblages can be detected, despite the existence of some erratic site‐specific changes. 6. Most of the species that showed large seasonal variations in density occupy temporary ponds during the rainy season, when much of the valley is inundated and pond networks form adjacent to streams. Short‐duration lateral migrations to these ponds may play an important role in the seasonal fish‐assemblage dynamics in Amazonian headwater streams. 7. Our results contrast with previous studies on small Amazonian streams, which have found little seasonal change in fish assemblages, and highlight the importance of the abundance of common species as an indicator of general fish assemblage structure in biological monitoring programmes.