Parasitic Gnathiid Isopods Research Articles

Nocturnal Infestation of Flounder (Bothidae: Pleuronectiformes) by Parasitic Gnathiid Isopods in the Central Philippines

We present observations of fish-parasitic gnathiid isopods infesting bothid flounders at night in shallow reef habitat in the central Philippines.

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.

Predation on parasitic gnathiid isopods on coral reefs: a comparison of Caribbean cleaning gobies with non-cleaning microcarnivores

On coral reefs, gnathiid isopods are a common blood-feeding ectoparasite of reef fishes that can have significant impacts on reef-fish health and fitness. Cleaner fishes and shrimps are the only major documented predators of gnathiids, removing them from the bodies of host fishes. However, gnathiids spend most of their lifecycle free living and thus may be eaten by other microcarnivorous fishes that collectively could have larger impacts on gnathiid populations. This study examined gut contents from Caribbean nocturnal reef microcarnivorous fish and from the Caribbean cleaning goby Elacatinus evelynae for the presence of gnathiid isopods. Among nocturnal microcarnivores, gnathiids were found in only a small proportion of the gut contents of grunts (5%) and cardinalfish (4%), but in a higher proportion of the gut contents of squirrelfish and soldierfish (26%). In comparison, most cleaning gobies collected in the morning had gnathiids (93%), with an average of 6.3 gnathiids per fish. While microcarnivorous fishes ate far fewer gnathiids, they were present in much greater numbers than cleaning gobies. These results support previous studies on cleaning gobies suggesting that individually, they consume high numbers of gnathiids. However, they also suggest that collectively, other predators could have an equal or greater impact on gnathiid populations.

Fish mucus versus parasitic gnathiid isopods as sources of energy and sunscreens for a cleaner fish

The cleaning behaviour of the bluestreak cleaner wrasse Labroides dimidiatus is extensively used as a model system for understanding cooperation. It feeds mainly on blood-sucking gnathiid isopods and also on the epidermal mucus of client fish; the nutritional quality of these foods, however, is unknown. The epidermal mucus of reef fish contains ultraviolet (UV)-absorbing compounds (mycosporine-like amino acids, MAAs), which are only obtained via the diet; nevertheless, while La. dimidiatus has high amounts of MAAs in its mucus, their source is unknown. Therefore, the energetic value (calories and protein estimated using carbon and nitrogen) and MAA level in gnathiids and mucus from several clients [parrotfishes, wrasses (Labridae), and a snapper (Lutjanidae)] were determined. The energetic value of mucus and gnathiids varied among fishes. Overall, carbon, nitrogen, calories, and protein per dry weight were higher in the mucus of most client species compared to gnathiids. Thus, depending on the client species, mucus may be energetically more advantageous for cleaner wrasse to feed on than gnathiids. UV absorbance, a confirmed proxy for MAA levels, indicated high MAA levels in mucus, whereas gnathiids had no detectable MAAs. This suggests that La. dimidiatus obtain MAAs from mucus but not from gnathiids. Hence, in addition to energy, the mucus of some clients also provides La. dimidiatus with the added bonus of UV-absorbing compounds. This may explain why cleaner fish prefer to feed on mucus over gnathiid isopods. The likely costs and benefits to clients of the removal of UV protecting mucus and parasitic gnathiids, respectively, and the variation in benefits gained by cleaner fish from feeding on these foods may explain some variation in cooperation levels in cleaning interactions.

Low susceptibility of invasive red lionfish (Pterois volitans) to a generalist ectoparasite in both its introduced and native ranges.

Escape from parasites in their native range is one of many mechanisms that can contribute to the success of an invasive species. Gnathiid isopods are blood-feeding ectoparasites that infest a wide range of fish hosts, mostly in coral reef habitats. They are ecologically similar to terrestrial ticks, with the ability to transmit blood-borne parasites and cause damage or even death to heavily infected hosts. Therefore, being highly resistant or highly susceptible to gnathiids can have significant fitness consequences for reef-associated fishes. Indo-Pacific red lionfish (Pterois volitans) have invaded coastal habitats of the western tropical and subtropical Atlantic and Caribbean regions. We assessed the susceptibility of red lionfish to parasitic gnathiid isopods in both their native Pacific and introduced Atlantic ranges via experimental field studies during which lionfish and other, ecologically-similar reef fishes were caged and exposed to gnathiid infestation on shallow coral reefs. Lionfish in both ranges had very few gnathiids when compared with other species, suggesting that lionfish are not highly susceptible to infestation by generalist ectoparasitic gnathiids. While this pattern implies that release from gnathiid infestation is unlikely to contribute to the success of lionfish as invaders, it does suggest that in environments with high gnathiid densities, lionfish may have an advantage over species that are more susceptible to gnathiids. Also, because lionfish are not completely resistant to gnathiids, our results suggest that lionfish could possibly have transported blood parasites between their native Pacific and invaded Atlantic ranges.

Live coral repels a common reef fish ectoparasite

Coral reefs are undergoing rapid changes as living corals give way to dead coral on which other benthic organisms grow. This decline in live coral could influence habitat availability for fish parasites with benthic life stages. Gnathiid isopod larvae live in the substratum and are common blood-feeding parasites of reef fishes. We examined substrate associations and preferences of a common Caribbean gnathiid, Gnathia marleyi. Emergence traps set over predominantly live coral substrata captured significantly fewer gnathiids than traps set over dead coral substrata. In laboratory experiments, gnathiids preferred dead coral and sponge and tended to avoid contact with live coral. When live gnathiids were added to containers with dead or live coral, significantly fewer were recovered from the latter after 24 h. Our data therefore suggest that live coral is not suitable microhabitat for parasitic gnathiid isopods and that a decrease in live coral cover increases available habitat for gnathiids.

The role of vision in host-finding behaviour of the ectoparasite Gnathia falcipenis (Crustacea; Isopoda)

Gnathiids are common isopod crustaceans that feed on blood and plasma from a wide range of reef fishes. Although parasitic gnathiid isopods are active during both day and night on the Great Barrier Reef, little is known about their behaviour and ecology due to difficulty with species identification. Information about nocturnal gnathiids is especially lacking because of logistical constraints. This study shows that a gnathiid species captured at night, Gnathia falcipenis, has a larger eye diameter than that of a taxonomically undescribed sympatric diurnal species, Gnathia sp. A. When tested in a phototaxis experiment with this diurnal species, G. falcipenis moved towards a light source at much lower levels of light intensity than the diurnal species. Their willingness to feed in lab tests with live host fish was also strongly linked to light conditions. This gnathiid appears to have visual adaptations that have evolved for foraging under very low light levels, and is probably completely nocturnal. These results are discussed with reference to the availability of different host fishes during the day and night, the risk of predation that gnathiids may encounter during these periods, and the possibility of an unappreciated diversity of gnathiid taxa that may have a range of foraging strategies.

Diel infestation dynamics of gnathiid isopod larvae parasitic on Caribbean reef fish

Infestation dynamics of parasitic gnathiid isopods on Caribbean reefs were studied throughout the 24-h diel cycle. Gnathiid infestation on caged longfin damselfish (Stegastes diencaeus) peaked strongly at dawn, remained low during the remainder of the day, and increased again at night until about midnight. Gnathiids were less abundant during the pre-dawn period. Peak loads on fish retrieved at dawn were the highest reported in any study thus far. The dawn peak consisted almost exclusively of individuals from the smallest size class, whereas nocturnal activity consisted almost exclusively of individuals of the largest size class. Because of the high rates of infestation at night and dawn, and the high variation in parasite loads on fish collected during that time, reduction of parasite infestation may play an important role in the selection of nocturnal and crepuscular shelter holes and settlement sites by reef fishes.

Reproductive and feeding ecology of parasitic gnathiid isopods of epaulette sharks ( Hemiscyllium ocellatum) with consideration of their role in the transmission of a haemogregarine

Epaulette sharks Hemiscyllium ocellatum were surveyed on Heron Island, Great Barrier Reef, Australia for gnathiid isopods and protozoan (haemogregarine) parasites to determine the prevalence and intensity of infection and to investigate the potential role of gnathiids as vectors of these haemogregarines, the first such study carried out on elasmobranchs. Juvenile gnathiids were collected and quantified using a novel non-invasive and chemical-free technique and gnathiid squashes were examined for haemogregarine developmental stages. The feeding and reproductive ecology of the Gnathia spp. was investigated to better understand the relationship between gnathiids and haemogregarines. Gnathiids were found on all sharks and intensities ranged between two and 66. Only third-stage gnathiid juveniles were found, which fell into two size groups (A and B). These juveniles remained attached to H. ocellatum for up to 17 days, the longest period of attachment yet recorded for gnathiids. Group A female gnathiids produced broods of 45–187 (median =120) first stage juveniles from between 54 and 82 days (median=63 days) after detachment. First stage juveniles survived for an average of 15.8±0.1 (SEM) days without feeding. The prevalence (6.7%) and parasitaemia (usually <0.1% infected erythrocytes) of infections of the haemogregarine Haemogregarina hemiscyllii were relatively low and most stages were immature gamonts. Two undescribed Gnathia spp. were identified by examining adult male gnathiids that metamorphosed from juveniles from each of the two size groups. Our hypothesis that Gnathia spp. transmit H. hemiscyllii is neither supported or refuted, as although intact H. hemiscyllii gamonts were detected in squashes of gnathiids that had engorged on haemogregarine-positive H. ocellatum 24–57 days previously, no further developmental stages were detected.

Cleaner fish, Labroides dimidiatus, diet preferences for different types of mucus and parasitic gnathiid isopods

Cleaner fish, Labroides dimidiatus, prefer the mucus of the parrotfish, Chlorurus sordidus, to parasitic gnathiid isopods, the main items in their diet, indicating a major conflict between clients and cleaners over what the latter should eat during interactions. We tested whether the conflict varied with client species (and the quality of its mucus) and with the presence of blood in the gnathiids. First, we offered cleaners the choice between mucus of the parrotfish and that of the snapper, Lutjanus fulviflamma. When offered equal amounts of mucus on Plexiglas plates, cleaners readily developed a significant preference for the parrotfish mucus. Reducing the amount of parrotfish mucus by 75% made the preference disappear. In a second test, we offered the cleaners gnathiids that were or were not engorged with client fish blood. Cleaners showed no significant preference for either food item. Our results suggest that the degree of conflict between cleaners and clients may vary between species, depending on whether the latter have a preferred mucus. In contrast, the cleaners' lack of preference for engorged gnathiids benefits clients because it means that cleaners do not hesitate to eat unengorged gnathiids before the gnathiids harm the fish by removing blood or by transmitting blood parasites.

Feeding ecology of the fish ectoparasite Gnathia sp. (Crustacea: Isopoda) from the Great Barrier Reef, and its implications for fish cleaning behaviour

The feeding rate of a parasitic gnathiid isopod on fish was examined. Individual fish, Hemigymnus melapterus, were exposed to gnathiid larvae and sampled after 5, 10, 30, 60, and 240 min. I recorded whether larvae had an engorged gut, an engorged gut containing red material, or had dropped off the fish after having completed engorgement; variation among sampling times and larval stages was analyzed using generalized linear mixed model analyses. The likelihood that larvae had an engorged gut increased with time and varied with larval stage. First stage ( 1.45 mm) larvae. After 30 min, however, most (>93%) larvae had an engorged gut regardless of their larval stage. The likelihood of red material in the gut of third stage larvae increased over time (46% after 30 min, 70% after 60 min, and 86% after 240 min) while that of first and second stage larvae remained relatively low (<27%) at all times. First and second stage larvae left the fish at a higher rate (approximately 23% after 30 min and 81% after 60 min) than third stage larvae (3% after 30 min and 26% after 60 min). After 60 min, however, the likelihood that larvae dropped off fish did not change. The variation in feeding behaviour with larval stage is likely due to variation in their diet and gut volume. The rapid feeding rate of gnathiid larvae suggests that their turnover rate on fish is high. This may explain why some fish species seek cleaner fish, which eat many gnathiid larvae, so often. By repeatedly visiting cleaner fish, gnathiids may also be removed from hosts before the parasites become fully engorged.

Do ectoparasites determine cleaner fish abundance? Evidence on two spatial scales

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 263:189-196 (2003) - doi:10.3354/meps263189 Do ectoparasites determine cleaner fish abundance? Evidence on two spatial scales Karen L. Cheney, Isabelle M. Côté* Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK *Corresponding author. Email: i.cote@uea.ac.uk ABSTRACT: Cleaner fish on coral reefs can have a significant impact on the diversity and distribution of their fish clients. Understanding the factors affecting the distribution of cleaners themselves therefore becomes an important consideration for elucidating the mechanisms controlling coral reef fish community structure. We hypothesised that obligate cleaner fish, which rely almost exclusively on ectoparasites gleaned from clients, should be more abundant in areas rich in their preferred prey, namely parasitic gnathiid isopod larvae. We tested predictions from this hypothesis on 2 spatial scales in the Caribbean: among reefs within Barbados, and among 6 islands spanning the Greater and Lesser Antilles. As predicted, densities of coral-dwelling cleaning gobies Elacatinus spp., which are active cleaners, were higher in areas of high rates of emergence of gnathiid larvae from the benthos. This relationship was not observed in sponge-dwelling cleaning gobies, which rely mainly on non-client-gleaned food sources. The density of coral-dwelling cleaners was also correlated with client density, but contrary to our prediction was not related to ectoparasite loads of a common reef fish client. Cleaning goby abundance is more likely to be a consequence than a cause of ectoparasite availability, since cleaning goby recruitment is usually linked to factors related to foraging, and territorial clients do not preferentially settle near cleaning gobies. Whether the link between cleaner abundance and ectoparasite availability is mediated through differential recruitment or differential survival of cleaners in parasite-rich and parasite-poor areas remains to be determined. KEY WORDS: Cleaning symbiosis · Reef fish community structure · Gobiosoma spp. Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 263. Online publication date: November 28, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Are Caribbean cleaning symbioses mutualistic? Costs and benefits of visiting cleaning stations to longfin damselfish

Cleaning symbioses in the marine environment have long been held to be mutualistic interactions in which cleaners glean food from the surface of their fish clients while client ectoparasite load is reduced. However, there is limited evidence to show that clients benefit from being cleaned. We investigated the nature of a cleaner–client relationship by quantifying the costs to territorial longfin damselfish, Stegastes diencaeus, of being cleaned by cleaning gobies (Elacatinus evelynae and E. prochilos) in terms of travelling time, aggression and territorial intrusions incurred while seeking cleaners, and the benefits in terms of reduction in ectoparasite load. Travelling time to seek cleaners increased with distance from a damselfish's territory, as did the number of aggressive attacks by other territorial fish sustained by the travelling damselfish. The number of intrusions by fish on to the unguarded territory also increased, although not significantly, with time spent away from the territory. As a result, damselfish visited cleaning stations less as the distance between its territory and cleaning station increased. This variation in visit rate was related to a slight but significant reduction in the number of parasitic gnathiid isopod larvae per damselfish, suggesting that cleaning gobies significantly reduce client ectoparasite load. Longfin damselfish appeared willing to pay only limited costs to be cleaned. They travelled much further and stayed away longer from their territories to perform reproductive and social activities than they did to seek cleaners. Distance-dependent variability in the costs of seeking cleaners allows damselfish to scale these costs in relation to the benefits gained and ensure that their relationship with cleaners remains mutualistic.

Diurnal variation in the abundance of juvenile parasitic gnathiid isopods on coral reef fish: implications for parasite-cleaner fish interactions

The dynamics of parasitic gnathiid isopod infestation on the fish Henzigymnus melapterus were examined at Heron Island, Great Barrier Reef, by measuring the abundance and feeding state of gnathiids on fish collected between dawn and sunset and by estimating the time required for gnathiids to become engorged on host fluids. A model was developed to estimate gnathiid abundance on fish for any given time of day and host size. Fish at dawn had 2.4 times as many gnathiids compared with fish at sunset, indicating that some gnathiids infest fish overnight. Most gnathiids had engorged guts (72-86%); the proportion of empty guts and engorged guts did not differ in three time periods of collection( 1100 h). In the laboratory, gnathiids fed quickly with 75% of gnathiids exposed to fish for 4 h having engorged guts. The short time required for gnathiids to become engorged and the presence of gnathiids with empty guts throughout the day suggests that gnathiids also infest fish during the day. Thus gnathiids eaten by cleaner fish during the day may be replaced by other gnathiids during the day or night suggesting that interactions between gnathiids and cleaner fish are highly dynamic.

Cleaner fish really do clean

The cleaning of client fish by cleaner fish is one of the most highly developed interspecific communication systems known. But even though it is a seemingly obvious mutualism1,2, several quantitative studies3,5 have failed to show any benefit for the clients, leading to the hypothesis that cleaner fish are ‘behavioural parasites’ that exploit the sensory system of the clients6 to obtain food, rather than to increase the client's fitness. The cleaner fish Labroides dimidiatus eats parasitic gnathiid isopods, which decline in number on the client fish Hemigymnus melapterus daily between dawn and sunset7,8. I find that the cleaner fish reduces parasite abundance, resulting in a 4.5-fold difference within 12 hours, supporting the hypothesis that cleaning behaviour is mutualistic.

Intraspecific and interspecific relationships between host size and the abundance of parasitic larval gnathiid isopods on coral reef fishes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 164:263-271 (1998) - doi:10.3354/meps164263 Intraspecific and interspecific relationships between host size and the abundance of parasitic larval gnathiid isopods on coral reef fishes Alexandra S. Grutter1,*, Robert Poulin2 1Department of Parasitology, The University of Queensland, Brisbane, Queensland 4072, Australia 2Department of Zoology, University of Otago, PO Box 56, Dunedin, New Zealand *E-mail: a.grutter@mailbox.uq.edu.au Parasitic gnathiid isopod larvae on coral reef teleosts and elasmobranchs were quantified at Lizard and Heron Islands (Great Barrier Reef), and Moreton Bay, Australia. The relationship between gnathiid abundance and host size was examined across and within species. Of the 56 species examined, 70% had gnathiids, with counts ranging from 1 to 200 per fish and the elasmobranchs having the highest numbers. Pomacentrids rarely had gnathiids. In contrast, most labrids had gnathiids. Gnathiid abundance was positively correlated with host size in the species Chlorurus sordidus, Ctenochaetus striatus, Hemigymnus melapterus, Siganus doliatus, and Thalassoma lunare, but not for Scolopsis bilineatus. Mean gnathiid abundance per host species also correlated with host size across species, even after controlling for the potential confounding effects of uneven sampling effort and host phylogeny. Thus host size explains much of the intraspecific and interspecific variation in gnathiid abundance on fish. Gnathiidae · Ectoparasites · Coral reef fish · Host-parasite interactions · Fish size · Great Barrier Reef Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 164. Publication date: April 09, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Size‐selective predation by the cleaner fish Labroides dimidiatus

A comparison of the size‐frequency distribution of parasitic gnathiid isopod larvae in the diet of the cleaner fish Labroides dimidiatus and on six host fish species (Chlorurus sordidus, Ctenochaetus striatus, Hemigymnus melapterus, Scolopsis bilineatus, Siganus doliatus, Thalassoma lunare) was made on one occasion. The comparison was repeated with Hemigymnus melapterus on three occasions and between two islands in Australia. L. dimidiatus selected larger gnathiids at all times at Lizard Island but not at Heron Island. Size‐selective predation by L. dimidiatus suggests any potential effect of cleaner fish on parasites may vary according to the size of parasite. However, this effect appears to vary spatially.

Spatiotemporal Variation and Feeding Selectivity in the Diet of the Cleaner Fish Labroides dimidiatus

The composition of the diet of the cleaner wrasse Labroides dimidiatus was quantified at different times and at tao spatial scales. I examined feeding selectivity in the cleaner fish by comparing its diet to the parasite: load of seven species of fish hosts it regularly cleans. Parasitic gnathiid isopods made up 50% of the estimated food volume and 95% of the prey items of Labroides dimidiatus at Lizard Island, Australia. The remaining 50% of the food material mainly was unidentified digested organic matter. Tnf greatest difference in the diet occurred between Heron and Lizard Islands, with only small differences among sites at the latter The total biomass of gnathiid isopods in the diet was four times higher at Lizard Island than at Heron Island, Fish from Lizard Island contained more caligid larvae and other parasitic copepods in their diet, whereas fish from Heron Island contained more nonparasitic copepods and mucus. The number and estimated biomass of gnathiids in the diet more than doubled from May to January. Variation in the diet implies spatial and temporal flexibility in the foraging patterns of L. dimidiatus. The higher ratio of gnathiids to other crustacea in the diet compared to that on host fish, suggests that L. dimidiatus is a selective feeder.