Variation in the parasite communities of three co-occurring herbivorous coral reef fishes.

Parasites are important, diverse, and abundant components of natural ecosystems and can influence the behaviour and health of their hosts, inter- and intraspecific interactions, and ultimately community structure. Coral reefs are one of the world's most biodiverse ecosystems, yet our understanding of the abundance, diversity, and composition of parasite communities of coral reef fishes is limited. Here, the authors aimed to compare the abundance, richness and composition of parasite communities among three co-occurring herbivorous coral reef fishes (the barred rabbitfish Siganus doliatus, Ward's damsel Pomacentrus wardi and the obscure damsel Pomacentrus adelus) from an inshore reef of the Great Barrier Reef (GBR). In total, 3978 parasites (3869 endoparasites and 109 ectoparasites) from 17 families were recovered from 30 individuals of each of the three fish species (mean = 44 ± 22 s.e. parasites per fish; range = 0-1947 parasites per fish). The parasite communities of P. wardi and P. adelus were characterised by pennellid copepods, derogenid and lecithasterid digeneans and were distinct from those of S. doliatus that were characterised by a higher abundance of atractotrematid and gyliauchenid digeneans. The abundance and family richness of all parasites were greatest in S. doliatus (abundance: 22.1 ± 5.0 parasites per fish; richness: 3.2 ± 0.3 families per fish), intermediate in P. wardi (abundance: 4.8 ± 1.1 parasites per fish; richness: 2.3 ± 0.3 families per fish) and lowest in P. adelus (abundance: 1.4 ± 0.4 parasites per fish; richness: 0.9 ± 0.2 families per fish). Similarly, the abundance of endoparasites was greatest in S. doliatus (19.7 ± 5.1 endoparasites per fish), intermediate in P. wardi (2.6 ± 0.7 endoparasites per fish) and lowest in P. adelus (1.2 ± 0.4 endoparasites per fish). Ectoparasite abundances were also lowest for P. adelus (0.2 ± 0.1 ectoparasites per fish), and S. doliatus and P. wardi had comparable abundances of ectoparasites (1.3 ± 0.3 and 2.1 ± 0.5 parasites per fish, respectively). Similarities between the parasite assemblages of the two pomacentrids may be related to their similar behaviours and/or diets vs. those of the larger-bodied and more mobile rabbitfish. Investigating the causes and consequences of variation in parasite communities across a broader range of fish species will be critical to understand the potential role of parasites in coral reef ecosystems.

Cleaner fish are potential super-spreaders.

Cleaning symbiosis is critical for maintaining healthy biological communities in tropical marine ecosystems. However, potential negative impacts of mutualism, such as the transmission of pathogens and parasites during cleaning interactions, have rarely been evaluated. Here, we investigated whether the dedicated bluestreak cleaner wrasse, Labroides dimidiatus, is susceptible to and can transmit generalist ectoparasites between client fish. In laboratory experiments, L. dimidiatus were exposed to infective stages of three generalist ectoparasite species with contrasting life histories. Labroides dimidiatus were susceptible to infection by the gnathiid isopod Gnathia aureamaculosa, but were significantly less susceptible to the ciliate protozoan Cryptocaryon irritans and the monogenean flatworm Neobenedenia girellae, compared with control host species (Coris batuensis or Lates calcarifer). The potential for parasite transmission from a client fish to the cleaner fish was simulated using experimentally transplanted mobile adult (i.e. egg-producing) monogenean flatworms on L. dimidiatus. Parasites remained attached to cleaners for an average of 2 days, during which parasite egg production continued, but was reduced compared with that on control fish. Over this timespan, a wild cleaner may engage in several thousand cleaning interactions, providing numerous opportunities for mobile parasites to exploit cleaners as vectors. Our study provides the first experimental evidence that L. dimidiatus exhibits resistance to infective stages of some parasites yet has the potential to temporarily transport adult parasites. We propose that some parasites that evade being eaten by cleaner fish could exploit cleaning interactions as a mechanism for transmission and spread.

DNA profiling reveals Neobenedenia girellae as the primary parasitic monogenean in global fisheries and aquaculture.

Accurate identification of parasite species and strains is crucial to mitigate the risk of epidemics and emerging disease. Species of Neobenedenia are harmful monogenean ectoparasites that infect economically important bony fishes in aquaculture worldwide, however, the species boundaries between two of the most notorious taxa, N. melleni and N. girellae, has been a topic of contention for decades. Historically, identifications of Neobenedenia isolates have overwhelmingly been attributed to N. melleni, and it has been proposed that N. girellae is synonymous with N. melleni. We collected 33 Neobenedenia isolates from 22 host species spanning nine countries and amplified three genes including two nuclear (Histone 3 and 28S rDNA) and one mitochondrial (cytochrome b). Four major clades were identified using Maximum Likelihood and Bayesian inference analyses; clades A-D corresponding to N. girellae, N. melleni, N. longiprostata and N. pacifica, respectively. All unidentified isolates and the majority of Neobenedenia sequences from GenBank fell into clade A. The results of this study indicate that N. girellae is a separate species to N. melleni, and that a large proportion of previous samples identified as N. melleni may be erroneous and a revision of identifications is needed. The large diversity of host species that N. girellae is able to infect as determined in this study and the geographic range in which it is present (23.8426°S and 24.1426°N) makes it a globally cosmopolitan species and a threat to aquaculture industries around the world.

Molecular and morphological evidence for the widespread distribution of Laticola paralatesi infecting wild and farmed Lates calcarifer in Australia.

Infections with monogeneans of the Diplectanidae can limit productivity of and cause considerable health issues for fish in aquaculture. To date, 9 species of diplectanids have been reported from the Asian sea bass or barramundi Lates calcarifer (Perciformes: Latidae) in the Asia-Pacific region. This study characterised the diplectanid parasite fauna found infecting wild and farmed barramundi from 5 localities in tropical Australia, including north Queensland and Western Australia. A combination of morphometric and comparative genetic analyses of partial 28S ribosomal RNA (28S rRNA) from specimens recovered were used to confirm their identity and to explore relationships with other diplectanids. These data revealed that a single, dominant species of diplectanid, Laticola paralatesi, infects wild and farmed Lates calcarifer in tropical Australia. Laticola lingaoensis Yang, Kritsky, Sun, Jiangying, Shi & Agrawal, 2006 is synonymised with L. seabassi (Wu, Li, Zhu & Xie, 2005) Domingues & Boeger, 2008 based on the combination of the host infected (Lates calcarifer), geographic distribution, distinct morphological similarity, and identical 28S rRNA sequence data identified here. Laticola seabassi is now designated as the type species of Laticola due to nomenclatural priority.

Effects of temperature and salinity on the life cycle of Neobenedenia sp. (Monogenea: Capsalidae) infecting farmed barramundi (Lates calcarifer).

Effective parasite management can be achieved through strategically timed treatments that break the life cycle. We examined the effects of temperature (2 °C increments from 22 to 34 °C) and salinity (0, 11, 22, 35, 40‰) on the life cycle (embryonation period, hatching success, oncomiracidia (larvae) longevity, infection success, and time to sexual maturity) of Neobenedenia sp. (Monogenea: Capsalidae), a harmful ectoparasite of farmed marine fishes. Experiments were conducted in controlled conditions in the laboratory. The life cycle was faster in warm, high saline conditions compared to cooler conditions (10-13 days between 26-32 °C, 40‰; 15-16 days between 22-24 °C at 40‰). Warm seawater and high saline conditions (24-32 °C, 35-40‰) improved egg hatching success, reduced time to sexual maturity, and resulted in parasites reaching sexual maturity at a larger size (at 30-32 °C) compared to cooler conditions (22 °C). In contrast, cool, hypersaline conditions (22 °C, 40‰) increased oncomiracidia longevity and infection success. Linear and quantile regression models were used to construct an interactive, online parasite management interface to enable strategic treatment of parasites in aquaculture corresponding to observed temperature and salinity variation on farms in the tropics. It was recommended that farmers treat their stock more frequently during summer (27-31 °C) when parasites can complete their life cycle more quickly. Nevertheless, farmers should be aware of the potential for increased Neobenedenia sp. infections during winter months (21-26 °C) due to increased infection success.

How do fishes manage disease?

Disease drives the evolution of proactive and reactive mitigation behaviours in fishes as for terrestrial animals. Understanding fish self-remedy behaviours could discover algal bioactives, reveal novel strategies for disease management, identify new habitats or ecosystems critical to population health and conservation, and enhance knowledge of interspecific evolutionary relationships and communication.

Assigning cause for emerging diseases of aquatic organisms.

Resolving the cause of disease (= aetiology) in aquatic organisms is a challenging but essential goal, heightened by increasing disease prevalence in a changing climate and an interconnected world of anthropogenic pathogen spread. Emerging diseases play important roles in evolutionary ecology, wildlife conservation, the seafood industry, recreation, cultural practices, and human health. As we emerge from a global pandemic of zoonotic origin, we must focus on timely diagnosis to confirm aetiology and enable response to diseases in aquatic ecosystems. Those systems' resilience, and our own sustainable use of seafood, depend on it. Synchronising traditional and recent advances in microbiology that span ecological, veterinary, and medical fields will enable definitive assignment of risk factors and causal agents for better biosecurity management and healthier aquatic ecosystems.

An Efficient Tetraplex Surveillance Tool for Salmonid Pathogens.

Fish disease surveillance methods can be complicated and time consuming, which limits their value for timely intervention strategies on aquaculture farms. Novel molecular-based assays using droplet digital Polymerase Chain Reaction (ddPCR) can produce immediate results and enable high sample throughput with the ability to multiplex several targets using different fluorescent dyes. A ddPCR tetraplex assay was developed for priority salmon diseases for farmers in New Zealand including New Zealand Rickettsia-like organism 1 (NZ-RLO1), NZ-RLO2, Tenacibaculum maritimum, and Yersinia ruckeri. The limit of detection in singleplex and tetraplex assays was reached for most targets at 10-9 ng/µl with, respectively, NZ-RLO1 = 0.931 and 0.14 copies/µl, NZ-RLO2 = 0.162 and 0.21 copies/µl, T. maritimum = 0.345 and 0.93 copies/µl, while the limit of detection for Y. ruckeri was 10-8 with 1.0 copies/µl and 0.7 copies/µl. While specificity of primers was demonstrated in previous studies, we detected cross-reactivity of T. maritimum with some strains of Tenacibaculum dicentrarchi and Y. ruckeri with Serratia liquefaciens, respectively. The tetraplex assay was applied as part of a commercial fish disease surveillance program in New Zealand for 1 year to demonstrate the applicability of tetraplex tools for the salmonid aquaculture industry.

Effects of Harmful Algal Blooms on Fish and Shellfish Species: A Case Study of New Zealand in a Changing Environment.

Harmful algal blooms (HABs) have wide-ranging environmental impacts, including on aquatic species of social and commercial importance. In New Zealand (NZ), strategic growth of the aquaculture industry could be adversely affected by the occurrence of HABs. This review examines HAB species which are known to bloom both globally and in NZ and their effects on commercially important shellfish and fish species. Blooms of Karenia spp. have frequently been associated with mortalities of both fish and shellfish in NZ and the sub-lethal effects of other genera, notably Alexandrium spp., on shellfish (which includes paralysis, a lack of byssus production, and reduced growth) are also of concern. Climate change and anthropogenic impacts may alter HAB population structure and dynamics, as well as the physiological responses of fish and shellfish, potentially further compromising aquatic species. Those HAB species which have been detected in NZ and have the potential to bloom and harm marine life in the future are also discussed. The use of environmental DNA (eDNA) and relevant bioassays are practical tools which enable early detection of novel, problem HAB species and rapid toxin/HAB screening, and new data from HAB monitoring of aquaculture production sites using eDNA are presented. As aquaculture grows to supply a sizable proportion of the world's protein, the effects of HABs in reducing productivity is of increasing significance. Research into the multiple stressor effects of climate change and HABs on cultured species and using local, recent, HAB strains is needed to accurately assess effects and inform stock management strategies.

Redescriptions of two species of microcotylid monogeneans from three arripid hosts in southern Australian waters.

Microcotyle arripis Sandars, 1945 is redescribed from Arripis georgianus from four localities: Spencer Gulf, Gulf St. Vincent, off Kangaroo Island and Coffin Bay, South Australia, Australia. Kahawaia truttae (Dillon & Hargis, 1965) Lebedev, 1969 is reported from A. trutta off Bermagui, New South Wales and is redescribed from a new host, A. truttaceus, from four localities in South Australian waters: Spencer Gulf, Gulf St. Vincent, off Kangaroo Island and Coffin Bay. Phylogenetic analysis of the partial 28S ribosomal RNA gene (28S rRNA) nucleotide sequences for both microcotylid species and comparison with other available sequence data for microcotylid species across four genera contributes to our understanding of relationships in this monogenean family.

Temperature alters reproduction and maternal provisioning in a fish ectoparasite.

This study quantified the effects of temperature on reproduction and maternal provisioning of the ectoparasite, Neobenedenia girellae (Platyhelminthes: Monogenea), a species known to cause detrimental impacts to aquaculture fishes in tropical and subtropical environments worldwide. At 20 and 25 °C, parasites exhibited relatively slower production of larger eggs that were energy-dense. In contrast, parasites at 30 °C attained sexual maturity faster, were reproductively active over a shorter period, grew to a smaller size and laid smaller, less energy-rich eggs at a faster rate. As such, parasites exhibited two distinct reproductive patterns in response to temperature: parasites at lower temperatures produced larger eggs with higher energy content, while those at the higher temperature had a higher rate of egg production. Larger eggs produced under cooler conditions were better provisioned with energetic reserves and important, membrane-bound lipids that would likely facilitate larval longevity and development success. This is commensurate with previous observations of epizootics of this parasite species in aquaculture systems during winter. Meanwhile, eggs produced at 30 °C contained higher proportions of saturated fatty acids compared with polyunsaturated fatty acids, likely reflecting metabolic regulation of cell membrane fluidity, which is necessary for larvae to survive warm conditions. This study demonstrates that fish ectoparasites have evolved substantial reproductive and metabolic flexibility to maximise infection success under variable environmental conditions.

Practical methods for culturing parasitic gnathiid isopods.

The reliance of parasites on their hosts makes host-parasite interactions ideal models for exploring ecological and evolutionary processes. By providing a consistent supply of parasites, in vivo monocultures offer the opportunity to conduct experiments on a scale that is generally not otherwise possible. Gnathiid isopods are common ectoparasites of marine fishes, and are becoming an increasing focus of research attention due to their experimental amenability and ecological importance as ubiquitous, harmful, blood-feeding "mosquito-like" organisms. They feed on hosts once during each of their three juvenile stages, and after each feeding event they return to the benthos to digest and moult to the next stage. Adults do not feed and remain in the benthos, where they reproduce and give birth. Here, we provide methods of culturing gnathiids, and highlight ways in which gnathiids can be used to examine parasite-host-environment interactions. Captive-raised gnathiid juveniles are increasingly being used in parasitological research; however, the methodology for establishing gnathiid monocultures is still not widely known. Information to obtain in vivo monocultures on teleost fish is detailed for a Great Barrier Reef (Australia) and a Caribbean Sea (US Virgin Islands) gnathiid species, and gnathiid information gained over two decades of successfully maintaining continuous cultures is summarised. Providing a suitable benthic habitat for the predominantly benthic free-living stage of this parasite is paramount. Maintenance comprises provision of adequate benthic shelter, managing parasite populations, and sustaining host health. For the first time, we also measured gnathiids' apparent attack speed (maximum 24.5 cm sec-1; 6.9, 4.9/17.0, median, 25th/75th quantiles) and illustrate how to collect such fast moving ectoparasites in captivity for experiments. In addition to providing details pertaining to culture maintenance, we review research using gnathiid cultures that have enabled detailed scientific understanding of host and parasite biology, behaviour and ecology on coral reefs.

Parasitic copepods of the family Lernanthropidae Kabata, 1979 (Copepoda: Siphonostomatoida) from Australian fishes, with descriptions of seven new species.

The total number of species of Lernanthropidae previously recorded from Australian waters is 15 (i.e., one species each of Aethon Krøyer, 1837, Lernanthropodes Bere, 1936, and Lernanthropsis Do, in Ho Do, 1985; 10 species of Lernanthropus de Blainville, 1822; and two species of Sagum Wilson, 1913), and all of these records are reviewed. We report here the presence of three species of Aethon. One species, A. garricki Hewitt, 1968, is reported from Australian waters for the first time and a new species, A. bicamera sp. nov., is described from the latrid, Latris lineatus (Forster, 1801) caught off South Australia. The genus Lernanthropodes is represented by a single species, L. trachinoti Pillai, 1962. We recognize Chauvanium Kazachenko, Kovaleva, Nguyen Ngo, 2017 as a subjective synonym of Lernanthropodes and transfer its type and only species C. chauvani Kazachenko, Kovaleva, Nguyen Ngo, 2017 which becomes Lernanthropodes chauvani (Kazachenko, Kovaleva, Nguyen Ngo, 2017) n. comb. Lernanthropsis mugilii (Shishido, 1898) is reported here from Mugil cephalus Linnaeus, 1758 sampled in Queensland and in New South Wales. The genus Lernanthropus is the most species rich and we report the presence of 20 nominal species on Australian marine fishes. This total includes six new species: L. alepicolus sp. nov. from Alepes apercna Grant, 1987, L. elegans sp. nov. from Atractoscion aequidens (Cuvier, 1830), L. gnathanodontus sp. nov. from Gnathanodon speciosus (Forsskål, 1775), L. paracruciatus sp. nov. from Protonibea diacanthus (Lacepède, 1802), L. pemphericola sp. nov. from Pempheris compressa (White, 1790), and L. selenotoca sp. nov. from Selenotoca multifasciata (Richardson, 1846). In addition, we report the presence of another four species in Australian waters for the first time: L. abitocephalus Tripathi, 1962, L. cadenati Delamare Deboutteville Nuñes-Ruivo, 1954, L. microlamini Hewitt, 1968, and L. pomadasysis Rangnekar Murti, 1961. After reexamination of the types of L. paenulatus Wilson, 1922 held in the USNM, we relegate this species to subjective synonymy with L. seriolii Shishido, 1898. Previous records of L. paenulatus from Australian Seriola species should be reassigned to L. seriolii. Lernanthropus ecclesi Kensley Grindley, 1973 is recognized as a junior subjective synonym of L. micropterygis Richiardi, 1884, and L. delamarei Marques, 1960, which is based on the male only, is tentatively considered to be a junior subjective synonym of L. micropterygis. Males are described for the first time for three species; L. breviculus Kabata, 1979, L. microlamini and L. mollis Kabata, 1979. A member of the genus Mitrapus Song Chen, 1976, M. oblongus (Pillai, 1964), is reported from Australia for the first time, on Herklotsichthys castelnaui (Ogilby, 1897) caught off Queensland and New South Wales. Finally, two species of Sagum were previously known from Australia and here we add three more. Two of the newly reported species were originally described as species of Lernanthropus but we formally transfer them here to Sagum as S. lativentris (Heller, 1865) n. comb. and S. sanguineus (Song, in Song Chen, 1976) n. comb. The males of S. lativentris and S. vespertilio Kabata, 1979 are described for the first time. A key to the females of the 31 species of lernanthropids found in Australian waters is provided.

Morphological descriptions of the larval and first juvenile stages of the decorator crab Camposcia retusa (Latreille, 1829) from laboratory-reared material.

The complete larval and first crab stages of the decorator crab Camposcia retusa (Latreille, 1829) are described and illustrated based on laboratory-reared material for the first time. Specimens were obtained from larvae hatched from adult crabs collected from coral reefs of Queensland, Australia. Newly hatched larvae were successfully reared to settlement as the first-stage crabs. Larval development consisted of two zoeal stages and one megalopal stage. The morphology of each larval stage was compared with those available from a previous study using material from the Red Sea. Due to substantial differences in morphology of the second zoeal and megalopal stages between the two studies, we argue that these larval stages described by the earlier report may not be that of C. retusa. Finally, the morphological characters of both larval and first crab stages of C. retusa are also compared with the corresponding stages of previously reported Inachidae.

Speciation of the Paradeontacylix spp. (Sanguinicolidae) of Seriola dumerili. Two new species of the genus Paradeontacylix from the Mediterranean.

Two new species of teleost blood fluke belonging to the sanguinicolid genus Paradeontacylix are described from the greater amberjack, Seriola dumerili, i.e. Paradeontacylix ibericus n. sp. from the Iberian Peninsula and Paradeontacylix balearicus n. sp. from the Balearic Islands. P. ibericus n. sp. and P. balearicus n. sp. show morphological similarities with Paradeontacylix kampachi and Paradeontacylix grandispinus respectively, which occur in mixed infection in S. dumerili from Japan. Multivariate analysis of morphometrical data provided statistical evidence for the separation of four species. However, component by component analysis did not show statistically significant differences between P. balearicus and P. grandispinus. Molecular data based on rITS2 and mCO1 gene sequences also supported the separation into four species. Morphological and molecular data were used to examine phylogenetic relationships between Paradeontacylix species from S. dumerili and other species in the genus. The results coincided in revealing two main branches with P. kampachi+P. ibericus and (((P. grandispinus+P. balearicus) Paradeontacylix sanguinicoloides) Paradeontacylix godfreyi). Paradeontacylix odhneri, for which little data are available, was located basal in a separate branch. This is the only species of Paradeontacylix which parasitizes a non-carangid host which might probably explain the separation from the other species. Paired similarities between the Japanese and the Mediterranean species, despite the large geographic distance, could be explained by the speciation of parasite geminate lines before host separation by tectonic events. Consequently, geographic and historical isolation support the morphological and genetic differences leading to the evolution of the new species described here.

Cleaner shrimp are a sustainable option to treat parasitic disease in farmed fish.

Chemical use is widespread in aquaculture to treat parasitic diseases in farmed fish. Cleaner fish biocontrols are increasingly used in fish farming as an alternative to medicines. However, cleaner fish are susceptible to some of their clients' parasites and their supply is largely dependent on wild harvest. In comparison, cleaner shrimp are not susceptible to fish ectoparasites and they can be reliably bred in captivity. The effectiveness of shrimp in reducing parasites on farmed fish remained unexplored until now. We tested four cleaner shrimp species for their ability to reduce three harmful parasites (a monogenean fluke, a ciliate protozoan, and a leech) on a farmed grouper. All shrimp reduced parasites on fish and most reduced the free-living early-life environmental stages - a function not provided by cleaner fish. Cleaner shrimp are sustainable biocontrol candidates against parasites of farmed fish, with the peppermint cleaner shrimp reducing parasites by up to 98%.

Parasite Dispersal From the Ornamental Goldfish Trade.

Goldfish, Carassius auratus Linnaeus, 1758, are immensely popular ornamental cyprinid fish, traded in more than 100 countries. For more than 500 years, human translocation has facilitated the spread of goldfish globally, which has enabled numerous and repeated introductions of parasite taxa that infect them. The parasite fauna assemblage of goldfish is generally well documented, but few studies provide evidence of parasite coinvasion following the release of goldfish. This review provides a comprehensive synopsis of parasites that infect goldfish in farmed, aquarium-held, native, and invasive populations globally and summarises evidence for the cointroduction and coinvasion of goldfish parasites. More than 113 species infect goldfish in their native range, of which 26 species have probably coinvaded with the international trade of goldfish. Of these, Schyzocotyle acheilognathi (Cestoda: Bothriocephalidae), Ichthyophthirius multifiliis (Ciliophora: Ichthyophthiriidae), Argulus japonicus (Crustacea: Argulidae), Lernaea cyprinacea (Crustacea: Ergasilidae), Dactylogyrus anchoratus, Dactylogyrus vastator and Dactylogyrus formosus (Monogenea: Dactylogyridae) are common to invasive goldfish populations in more than four countries and are considered a high risk of continued spread. Coinvasive parasites include species with direct and complex life cycles, which have successfully colonised new environments through utilisation of either new native hosts or suitable invasive hosts. Specifically, I. multifiliis, A. japonicus and L. cyprinacea can cause harm to farmed freshwater fish species and are important parasites to consider for biosecurity. These species may threaten other aquatic animal industries given their low host specificity and adaptable life histories. Future attention to biosecurity, management and border detection methods could limit the continued spread of exotic parasites from the ornamental trade of goldfish.

Aquatic Parasite Cultures and Their Applications.

In this era of unprecedented growth in aquaculture and trade, aquatic parasite cultures are essential to better understand emerging diseases and their implications for human and animal health. Yet culturing parasites presents multiple challenges, arising from their complex, often multihost life cycles, multiple developmental stages, variable generation times and reproductive modes. Furthermore, the essential environmental requirements of most parasites remain enigmatic. Despite these inherent difficulties, in vivo and in vitro cultures are being developed for a small but growing number of aquatic pathogens. Expanding this resource will facilitate diagnostic capabilities and treatment trials, thus supporting the growth of sustainable aquatic commodities and communities.

Morphological variation in the cosmopolitan fish parasite Neobenedenia girellae (Capsalidae: Monogenea).

Intra-species morphological variation presents a considerable problem for species identification and can result in taxonomic confusion. This is particularly pertinent for species of Neobenedenia which are harmful agents in captive fish populations and have historically been identified almost entirely based on morphological characters. This study aimed to understand how the morphology of Neobenedenia girellae varies with host fish species and the environment. Standard morphological features of genetically indistinct parasites from various host fish species were measured under controlled temperatures and salinities. An initial field-based investigation found that parasite morphology significantly differed between genetically indistinct parasites infecting various host fish species. The majority of the morphological variation observed (60%) was attributed to features that assist in parasite attachment to the host (i.e. the posterior and anterior attachment organs and their accessory hooks) which are important characters in monogenean taxonomy. We then experimentally examined the effects of the interaction between host fish species and environmental factors (temperature and salinity) on the morphology of isogenic parasites derived from a single, isolated hermaphroditic N. girellae infecting barramundi, Lates calcarifer. Experimental infection of L. calcarifer and cobia, Rachycentron canadum, under controlled laboratory conditions did not confer host-mediated phenotypic plasticity in N. girellae, suggesting that measured morphological differences could be adaptive and only occur over multiple parasite generations. Subsequent experimental infection of a single host species, L. calcarifer, at various temperatures (22, 30 and 32 °C) and salinities (35 and 40‰) showed that in the cooler environments (22 °C) N. girellae body proportions were significantly smaller compared with warmer temperatures (30 and 32 °C; P < 0.0001), whereas salinity had no effect. This is evidence that temperature can drive phenotypic plasticity in key taxonomic characters of N. girellae under certain environmental conditions.

Metazoan parasite assemblages of wild Seriola lalandi (Carangidae) from eastern and southern Australia.

Yellowtail kingfish, Seriola lalandi support significant commercial and recreational fisheries as well as aquaculture operations throughout the world. Metazoan parasite infections of S. lalandi are of considerable economic and ecological importance, yet very little is known about wild parasite assemblages. S. lalandi were collected from the east coast and south coast of Australia and examined for metazoan parasites. Forty-three parasite taxa were identified, including 26 new host records. Four of the parasite species recovered have been previously associated with disease or mortality in Seriola aquaculture. Comparisons are made between ectoparasite and endoparasite prevalence and intensity of S. lalandi from New South Wales and Victoria. S. lalandi sampled from the east coast of Australia shared ectoparasites previously documented from this species in New Zealand, providing support that S. lalandi in the Tasman Sea comprise a single stock. Based on previously used criteria to evaluate the suitability of parasites as biological tags, the monogenean Paramicrocotyloides reticularis Rohde and the copepod Parabrachiella seriolae Yamaguti and Yamasu may be potentially useful for stock discrimination.