Effects of fishing on parasitism in a sparid fish: contrasts between two areas of the Western Mediterranean

Comprehensive annotated checklist of monogenean diversity and distribution in Algerian marine fish

A comprehensive checklist of monogenean parasites from marine fish in Algeria was compiled by reviewing the entire available literature, resulting in a detailed parasite-host and host-parasite list. This checklist includes 156 species across 71 genera and 23 families of monogeneans, with 136 species identified to the species level, while the remaining 20 species are identified only to the genus (19 species) or subfamily level (1 species). These parasites have been reported from 82 marine fish hosts, spanning 34 families: 15 species of Elasmobranchii, 1 of Holocephali, and 66 of Teleostei. The highest number of monogenean species was found on Teleostei (128), followed by Elasmobranchii (26), and Holocephali (2). The family Diplectanidae Monticelli, 1903 is the most prevalent, encompassing 43 species, followed by Microcotylidae Taschenberg, 1879 with 27 species. Among the most diverse genera are Lamellodiscus Johnston & Tiegs, 1922 and Microcotyle Van Beneden & Hesse, 1863, with the latter's species, Microcotyle erythrini, Van Beneden & Hesse, 1863 being the most encountered species. The class Teleostei has been the most extensively studied, with the Sparidae Rafinesque, 1818 family receiving the most attention, particularly Boops boops (Linnaeus) as the most cited fish species. Notably, Diplodus vulgaris (Geoffroy Saint-Hilaire) and Diplodus sargus (Linnaeus) exhibit high species richness. The checklist also identified seven Monogenea species, including Atriaster maillardi López-Román & De Armas Hernández, 1989, newly recorded in the Mediterranean. This checklist provides an up-to-date summary of Monogenea diversity in Algerian marine fish, reflecting nearly three decades of detailed taxonomic research. It highlights the current understanding of these parasites and underscores the need for continued research to fully explore the diversity of monogenean parasites in Algerian fish fauna.

Impact of anthropogenous environmental factors on the marine ecosystem of trophically transmitted helminths and hosting seabirds: Focus on North Atlantic, North Sea, Baltic and the Arctic seas

Alongside natural factors, human activities have a major impact on the marine environment and thus influence processes in vulnerable ecosystems. The major purpose of this review is to summarise the current understanding as to how manmade factors influence the marine biocenosis of helminths, their intermediate hosts as well as seabirds as their final hosts. Moreover, it highlights current knowledge gaps regarding this ecosystem, which should be closed in order to gain a more complete understanding of these interactions. This work is primarily focused on helminths parasitizing seabirds of the North Atlantic and the Arctic Ocean. The complex life cycles of seabird helminths may be impacted by fishing and aquaculture, as they interfere with the abundance of fish and seabird species, while the latter also affects the geographical distribution of intermediate hosts (marine bivalve and fish species), and may therefore alter the intertwined marine ecosystem. Increasing temperatures and seawater acidification as well as environmental pollutants may have negative or positive effects on different parts of this interactive ecosystem and may entail shifts in the abundance or regional distribution of parasites and/or intermediate and final hosts. Organic pollutants and trace elements may weaken the immune system of the hosting seabirds and hence affect the final host's ability to control the endoparasites. On the other hand, in some cases helminths seem to function as a sink for trace elements resulting in decreased concentrations of heavy metals in birds' tissues. Furthermore, this article also describes the role of helminths in mass mortality events amongst seabird populations, which beside natural causes (weather, viral and bacterial infections) have anthropogenous origin as well (e.g. oil spills, climate change, overfishing and environmental pollution).

A century of parasitology in fisheries and aquaculture

Fish parasitological research associated with fisheries and aquaculture has expanded remarkably over the past century. The application of parasites as biological tags has been one of the fields in which fish parasitology has generated new insight into fish migration and stock assessments worldwide. It is a well-established discipline whose methodological issues are regularly reviewed and updated. Therefore, no concepts or case-studies will be repeated here; instead, we summarize some of the main recent findings and achievements of this methodology. These include the extension of its use in hosts other than bony fishes; the improvements in the selection of parasite tags; the recognition of the host traits affecting the use of parasite tags; and the increasingly recognized need for integrative, multidisciplinary studies combining parasites with classical methods and modern techniques, such as otolith microchemistry and genetics. Archaeological evidence points to the existence of parasitic problems associated with aquaculture activities more than a thousand years ago. However, the main surge of research within aquaculture parasitology occurred with the impressive development of aquaculture over the past century. Protozoan and metazoan parasites, causing disease in domesticated fish in confined environments, have attracted the interest of parasitologists and, due to their economic importance, funding was made available for basic and applied research. This has resulted in a profusion of basic knowledge about parasite biology, physiology, parasite-host interactions, life cycles and biochemistry. Due to the need for effective control methods, various solutions targeting host-parasite interactions (immune responses and host finding), genetics and pharmacological aspects have been in focus.

No vagina, one vagina, or multiple vaginae? An integrative study of Pseudaxine trachuri (Monogenea, Gastrocotylidae) leads to a better understanding of the systematics of Pseudaxine and related genera

The presence/absence and number of vaginae is a major characteristic for the systematics of the Monogenea. Three gastrocotylid genera share similar morphology and anatomy but are distinguished by this character: Pseudaxine Parona & Perugia, 1890 has no vagina, Allogastrocotyle Nasir & Fuentes Zambrano, 1983 has two vaginae, and Pseudaxinoides Lebedev, 1968 has multiple vaginae. In the course of a study of Pseudaxine trachuri Parona & Perugia 1890, we found specimens with structures resembling "multiple vaginae"; we compared them with specimens without vaginae in terms of both morphology and molecular characterisitics (COI barcode), and found that they belonged to the same species. We also investigated the male copulatory organ (MCO) of this species, the accuracy of the original description of which is known to be a matter of debate. We found that the genital atrium is armed with 12 hooks arranged as a single circle and a central hollow stylet which is probably involved in traumatic insemination. We redescribed Pseudaxine trachuri based on newly collected specimens from off the coast of Algeria and Museum specimens from off France. Specimens from the type-host, Trachurus trachurus, were found to be similar, for both molecular sequences and morphology, to those found on Boops boops. We can therefore confirm, for the first time with molecular evidence, that B. boops is a host of this parasite. We consider that Pseudaxinoides was erected on the basis of an erroneous interpretation of structures which are not vaginae and, consequently, propose the transfer of most of its species to Pseudaxine, as P. australis (Lebedev, 1968) n. comb., P. bychowskyi (Lebedev, 1977) n. comb., P. caballeroi (Lebedev, 1977) n. comb., P. cariacoensis (Nasir & Fuentes-Zambrano, 1983) n. comb., and P. vietnamensis (Lebedev, Parukhin & Roitman, 1970) n. comb. We also propose Allogastrocotyle dillonhargisorum nom. nov. for Pseudaxine bivaginalis Dillon & Hargis, 1965 to avoid a secondary homonymy.

Parasitic nematodes of marine fishes from Palmyra Atoll, East Indo-Pacific, including a new species of Spinitectus (Nematoda, Cystidicolidae)

Here, we present the results of a taxonomic survey of the nematodes parasitizing fishes from the lagoon flats of Palmyra Atoll, Eastern Indo-Pacific. We performed quantitative parasitological surveys of 653 individual fish from each of the 44 species using the intertidal sand flats that border the atoll's lagoon. We provide morphological descriptions, prevalence, and mean intensities of the recovered seven species of adult nematode (Pulchrascaris chiloscyllii, Capillariidae gen. sp., Cucullanus bourdini, Cucullanus oceaniensis, Pseudascarophis sp., Spinitectus (Paraspinitectus) palmyraensissp. nov., Philometra pellucida) and three larval stages (Pulchrascaris sp., Hysterothylacium sp., Cucullanus sp.). We recorded: Pulchrascaris chiloscyllii from Carcharhinus melanopterus; Capillariidae gen. sp. from Chaetodon lunula, Lutjanus fulvus, and Ellochelon vaigiensis; Cucullanus bourdini from Arothron hispidus; Cucullanus oceaniensis from Abudefduf sordidus; Pseudascarophis sp. from Chaetodon auriga, Chaetodon lunula, and Mulloidichthys flavolineatus; Spinitectus (Paraspinitectus) palmyraensissp. nov. from Albula glossodonta; Philometra pellucida from Arothron hispidus; and three larval forms, Pulchrascaris sp. from Acanthurus triostegus, Acanthurus xanthopterus, Rhinecanthus aculeatus, Platybelone argalus, Carangoides ferdau, Carangoides orthogrammus, Caranx ignobilis, Caranx melampygus, Caranx papuensis, Chaetodon auriga, Chanos chanos, Amblygobius phalaena, Asterropteryx semipunctata, Valencienea sexguttata, Kyphosus cinerascens, Lutjanus fulvus, Lutjanus monostigma, Ellochelon vaigiensis, Mulloidichthys flavolineatus, Upeneus taeniopterus, Gymnothorax pictus, Abudefduf septemfasciatus, Abudefduf sordidus, and Stegastes nigricans; Hysterothylacium sp. type MD from Acanthurus triostegus, Carangoides ferdau, Chaetodon lunula, Chanos chanos, Kyphosus cinerascens, Abudefduf sordidus, and Arothron hispidus; and Cucullanus sp. from Caranx ignobilis. Spinitectus (Paraspinitectus) palmyraensissp. nov. (Cystidicolidae) is described from the intestine of roundjaw bonefish Albula glossodonta. All the nematode species reported in this study represent new geographical records. We discuss how our survey findings compare to other areas of the Indo-Pacific, and the way the relatively numerical dominance of trophically transmitted larval stages likely reflect the intact food web of Palmyra Atoll, which includes a large biomass of large-bodied top predator sharks and ray-finned fishes.

Metazoan parasite infracommunities of the dusky flounder (Syacium papillosum) as bioindicators of environmental conditions in the continental shelf of the Yucatan Peninsula, Mexico

Background

We assessed metrics of the metazoan parasite infracommunities of the dusky flounder (Syacium papillosum) as indicators of aquatic environmental health of the Yucatan Shelf (YS) prior to oil extraction. We sampled the dusky flounder and its parasites along the YS, mostly during the 2015 north wind season (November–April). Our aims were: (i) to determine whether the parasite infracommunity metrics of S. papillosum exhibit significant differences among YS subregions; (ii) to determine whether the probability of the occurrence of its parasite species and individuals were affected by environmental variables, nutrients, heavy metals and hydrocarbons at the seascape level; and (iii) to determine whether there were statistical differences between the parasite infracommunity metrics of S. papillosum from YS and those of Syacium gunteri from the Campeche Sound. Multivariate statistical analyses and generalised additive models (GAMs) were used to examine the potential statistical associations between the contaminants, environmental variables and parasite community metrics, and the maximum entropy algorithm (MaxEnt) was used to characterise the habitat’s suitability for the parasite’s probability of occurrence.

Results

We recovered 48 metazoan parasite species from 127 S. papillosum, with larval cestodes and digeneans being the most numerically-dominant. Multivariate analyses showed significant differences in parasite infracommunity metrics among Western YS, Mid YS and Caribbean subregions, with the latter being the richest in species but not in individuals. The GAM and MaxEnt results indicated a negative effect of top predators (e.g. sharks and rays) removal on parasite metrics. The parasite infracommunities of S. papillosum were twice as rich in the number of species and individuals as those reported for S. gunteri from the Campeche Sound.

Conclusions

The significant differences among subregions in parasite metrics were apparently due to the interruption of the Yucatan current during the north wind season. The fishing of top predators in combination with an influx of nutrients and hydrocarbons in low concentrations coincides with an increase in larval cestodes and digeneans in S. papillosum. The dusky flounder inhabits a region (YS) with a larger number of metazoan parasite species compared with those available for S. gunteri in the Campeche Sound, suggesting better environmental conditions for transmission in the YS.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3524-6) contains supplementary material, which is available to authorized users.

Towards the resolution of the Microcotyle erythrini species complex: description of Microcotyle isyebi n. sp. (Monogenea, Microcotylidae) from Boops boops (Teleostei, Sparidae) off the Algerian coast

The monogenean Microcotyle erythrini is atypical because it has been recorded from several fish host species in the Mediterranean Sea and Atlantic Ocean, in contrast to many species which are considered strictly specific. This could indicate a true lack of specificity or that several cryptic species are involved. This paper is a partial attempt to solve this problem. Specimens of a monogenean resembling M. erythrini were collected from bogues, Boops boops, caught off Algeria. A comparison with published descriptions and with museum specimens of M. erythrini did not yield any clear morphological difference. However, sequences of cytochrome c oxidase subunit I (COI) differed by 16.3% from that of M. erythrini (from GenBank, material collected from the type-host Pagellus erythrinus), indicating that the species was different. The species from B. boops is therefore described here as Microcotyle isyebi n. sp. and differential diagnoses with Microcotyle species from the Mediterranean and from sparids are provided. These results suggest that a molecular re-evaluation of other M. erythrini-like specimens from various fish hosts could reveal the existence of additional parasite biodiversity.

Microcotyle visa n. sp. (Monogenea: Microcotylidae), a gill parasite of Pagrus caeruleostictus (Valenciennes) (Teleostei: Sparidae) off the Algerian coast, Western Mediterranean

Parasite biodiversity of fish of the southern part of the Mediterranean sea is still incompletely explored. We describe here Microcotyle visa n. sp. from the gill filaments of the bluespotted seabream Pagrus caeruleostictus (Valenciennes) (Sparidae) collected off the Algerian coast. The identity of fish hosts was confirmed by barcoding. Microcotyle visa n. sp. is herein described and illustrated. Analysis of the cox1 gene of the monogeneans revealed minor intraspecific variation (1.4%), an order of magnitude lower than the distance between this species and other Microcotyle species (10-15 %). Microcotyle visa n. sp. is distinguished from Microcotyle erythrini van Beneden & Hesse, 1863, a congener infesting sparids, on the basis of morphological (size of clamps, number of testes) and molecular (cox1) differences. This is the fourth member of the genus known to parasitise a sparid host. A species of Paramicrocotyle sp. included in the molecular analysis was nested within a robust Microcotyle + Paramicrocotyle clade; in the absence of demonstrated molecular and morphological differences, we consider that Paramicrocotyle Caballero & Bravo-Hollis, 1972 is a junior synonym of Microcotyle van Beneden & Hesse, 1863 and transfer two species of Paramicrocotyle as Microcotyle danielcarrioni (Martinez & Barrantes, 1977) n. comb. and Microcotyle moyanoi (Villalba & Fernandes, 1986) n. comb.

Parasite communities of the white seabream Diplodus sargus sargus in the marine protected area of Medes Islands, north-west Mediterranean Sea

Marine protected areas are considered a useful tool to preserve and recover the biodiversity of ecosystems. It is suggested that fisheries not only affect populations of target and bycatch species but also their parasite communities. Parasites can indicate fishery effects on host species and also on the whole local community, but the effects of fisheries and protection measures on parasite communities are relatively unknown. This study analyses parasite communities of the white seabream Diplodus sargus sargus in order to assess potential effects exerted by protection measures within and by fisheries outside a reserve in the western Mediterranean Sea. This small scale analysis offered the opportunity to study different degrees of fishery effects on parasite infracommunities, without considering climatic effects as an additional factor. Parasite infracommunities of fishes from the no-take zone (NTZ) differed in their composition and structure compared with areas completely or partially open to fisheries. The detected spatial differences in the infracommunities derived from generalist parasites and varied slightly between transmission strategies. Monoxenous parasites were richer and more diverse in both fished areas, but more abundant in the no-take, whereas richness and abundance of heteroxenous parasites were higher for the NTZ. In addition to host body size as one factor explaining these spatial variations, differences within parasite infracommunities between the areas may also be linked to increased host densities and habitat quality since the implementation of the NTZ and its protection measures.

Long-term stability of Sphyrion lumpi abundance in beaked redfish Sebastes mentella of the Irminger Sea and its use as biological marker

The main commercial fish species in the Irminger Sea, the beaked redfish Sebastes mentella, is commonly infected with the copepod Sphyrion lumpi. This ectoparasite is often used as a biological marker for stock discrimination to evaluate the still-debated metapopulation structure of beaked redfish. Nevertheless, it is still not understood whether parasite abundances and communities vary over longer time periods. In the present study, we investigated the abundance of S. lumpi in S. mentella of the pelagic zone of the Irminger Sea and adjacent waters. Our analyses revealed that live S. lumpi abundance remained constant during summer over a sampling period from 2001 to 2015, which confirms its validity as a biomarker. As S. mentella forms dense aggregations during mating, our results suggest that host densities are, regardless of a fishery-induced decrease in host biomass, large enough to facilitate the direct transmission of S. lumpi. After correcting for covariate effects, two stock units could be differentiated, which supports a continuation of the current fishery management strategy.

Parasite communities in two sparid fishes from the western Mediterranean: a comparative analysis based on samples from three localities off the Algerian coast

We provide the first known comparative assessment of metazoan parasite communities in two taxonomically and ecologically related sparids, Boops boops and Spicara maena, that are common in the coastal infralittoral habitats in the Mediterranean. Using abundant data for infracommunities in three localities off the Algerian coasts of the Mediterranean, we tested the general prediction that the phylogenetic proximity of the two hosts, their overlapping geographical distribution and habitat occupation, as well as the similar feeding habits and diet would contribute to a homogenization of their parasite community composition and structure. The regional fauna of parasites of B. boops and S. maena along the Algerian coasts of the western Mediterranean was species-rich (36 species) and dominated by heteroxenous species (27 spp; of these 20 digenean spp.). The phylogenetic relatedness between the two hosts resulted in a large number of shared parasites (56 %, 20 spp.). However, the significant overlap in the parasite faunas of the two sparid hosts and their similar feeding habits and diet did not translate into homogeneous parasite community pattern; a significant differentiation in terms of both, composition and structure, was observed.

Sclerodistomoides pacificus Kamegai, 1971 (Sclerodistomoididae Gibson & Bray, 1979) and Tetrochetus coryphaenae Yamaguti, 1934 (Accacoeliidae Odhner, 1911), two rarely reported digeneans from Tylosurus acus imperialis (Rafinesque) (Belonidae), and a list of helminth parasites of Tylosurus acus (Lacépède)

Two rarely reported digenean parasites are redescribed: Sclerodistomoides pacificus Kamegai, 1971 (Sclerodistomoididae Gibson & Bray, 1979) from the gall bladder and Tetrochetus coryphaenae Yamaguti, 1934 (Accacoeliidae Odhner, 1911) from the digestive tract of the Mediterranean needlefish Tylosurus acus imperialis (Rafinesque) off Tunisia. Sclerodistomoides pacificus and T. coryphaenae represent new host and geographical records for T. a. imperialis off the Tunisian coast. A complete list of the helminth parasites found in T. a. imperialis and those reported from other subspecies of Tylosurus acus (Lacépède) throughout their wide distributional range is presented. It includes data for T. a. acus (Lacépède), T. a. imperialis, T. a. melanotus (Bleeker) and T. a. rafale Collette & Parin and comprises 46 parasite taxa. Among these, 15 species were recorded from T. a. imperialis off Tunisia.

Nematodes parasitizing Trachurus trachurus (L.) and Boops boops (L.) from Algeria

A total of 455 Boops boops (Linnaeus, 1758) and 953 Trachurus trachurus Linnaeus, 1758 from the east coast of Algeria were examined for their parasitic Nematoda. Two hundred ninety-five specimens of larval stages L3 and L4 were collected from the peritoneal cavity of these two examined fishes. Photonic and scanning electronic microscopy (SEM) studies were performed on these larvae specimens in order to characterize their morphology. Two different species of Nematoda (Anisikidae) were identified: Anisakis simplex (Rudolphi, 1809) and Hysterothylacium aduncum (Rudolphi, 1802). These two parasitic species were reported for the first time on T. trachurus and B. boops from the eastern coast of Algeria. These parasites were attached on different organs in the abdominal cavity (particularly on ovaries and testes). The infestation rate changed according to the month and the host size. The parasitism did not show a significant negative impact on the condition of the examined fishes.

Fishing drives declines in fish parasite diversity and has variable effects on parasite abundance

Despite the ubiquity and ecological importance of parasites, relatively few studies have assessed their response to anthropogenic environmental change. Heuristic models have predicted both increases and decreases in parasite abundance in response to human disturbance, with empirical support for both. However, most studies focus on one or a few selected parasite species. Here, we assess the abundance of parasites of seven species of coral reef fishes collected from three fished and three unfished islands of the Line Islands archipelago in the central equatorial Pacific. Because we chose fish hosts that spanned different trophic levels, taxonomic groups, and body sizes, we were able to compare parasite responses across a broad cross section of the total parasite community in the presence and absence of fishing, a major human impact on marine ecosystems. We found that overall parasite species richness was substantially depressed on fished islands, but that the response of parasite abundance varied among parasite taxa: directly transmitted parasites were significantly more abundant on fished than on unfished islands, while the reverse was true for trophically transmitted parasites. This probably arises because trophically transmitted parasites require multiple host species, some of which are the top predators most sensitive to fishing impacts. The increase in directly transmitted parasites appeared to be due to fishing-driven compensatory increases in the abundance of their hosts. Together, these results provide support for the predictions of both heuristic models, and indicate that the direction of fishing's impact on parasite abundance is mediated by parasite traits, notably parasite transmission strategies.

How have fisheries affected parasite communities?

To understand how fisheries affect parasites, we conducted a meta-analysis of studies that contrasted parasite assemblages in fished and unfished areas. Parasite diversity was lower in hosts from fished areas. Larger hosts had a greater abundance of parasites, suggesting that fishing might reduce the abundance of parasites by selectively removing the largest, most heavily parasitized individuals. After controlling for size, the effect of fishing on parasite abundance varied according to whether the host was fished and the parasite's life cycle. Parasites of unfished hosts were more likely to increase in abundance in response to fishing than were parasites of fished hosts, possibly due to compensatory increases in the abundance of unfished hosts. While complex life cycle parasites tended to decline in abundance in response to fishing, directly transmitted parasites tended to increase. Among complex life cycle parasites, those with fished hosts tended to decline in abundance in response to fishing, while those with unfished hosts tended to increase. However, among directly transmitted parasites, responses did not differ between parasites with and without fished hosts. This work suggests that parasite assemblages are likely to change substantially in composition in increasingly fished ecosystems, and that parasite life history and fishing status of the host are important in predicting the response of individual parasite species or groups to fishing.

Marine protected areas facilitate parasite populations among four fished host species of central Chile

1. Parasites comprise a substantial proportion of global biodiversity and exert important ecological influences on hosts, communities and ecosystems, but our knowledge of how parasite populations respond to human impacts is in its infancy. 2. Here, we present the results of a natural experiment in which we used a system of highly successful marine protected areas and matched open-access areas in central Chile to assess the influence of fishing-driven biodiversity loss on parasites of exploited fish and invertebrate hosts. We measured the burden of gill parasites for two reef fishes (Cheilodactylus variegatus and Aplodactylus punctatus), trematode parasites for a keyhole limpet (Fissurella latimarginata), and pinnotherid pea crab parasites for a sea urchin (Loxechinus albus). We also measured host density for all four hosts. 3. We found that nearly all parasite species exhibited substantially greater density (# parasites m(-2)) in protected than in open-access areas, but only one parasite species (a gill monogenean of C. variegatus) was more abundant within hosts collected from protected relative to open-access areas. 4. These data indicate that fishing can drive declines in parasite abundance at the parasite population level by reducing the availability of habitat and resources for parasites, but less commonly affects the abundance of parasites at the infrapopulation level (within individual hosts). 5. Considering the substantial ecological role that many parasites play in marine communities, fishing and other human impacts could exert cryptic but important effects on marine community structure and ecosystem functioning via reductions in parasite abundance.