Seaweed extracts as a natural control against the monogenean ectoparasite,Neobenedenia sp., infecting farmed barramundi (Lates calcarifer)

Aqueous extracts from common tropical seaweeds were evaluated for their effect on the life cycle of the commercially important ectoparasite, Neobenedenia sp. (Platyhelminthes: Monogenea), through the survival of attached adult parasites, period of embryonic development, hatching success and oncomiracidia (larvae) infection success. There was no significant effect of any extract on the survival of adult parasites attached to fish hosts or infection success by oncomiracidia. However, the extracts of two seaweeds, Ulva sp. and Asparagopsis taxiformis, delayed embryonic development and inhibited egg hatching. The extract of A. taxiformis was most effective, inhibiting embryonic development of Neobenedenia sp. and reducing hatching success to 3% compared with 99% for the seawater control. Furthermore, of the 3% of eggs that hatched, time to first and last hatch was delayed (days 14 and 18) compared with the seawater control (days 5 and 7). Asparagopsis taxiformis shows the most potential for development as a natural treatment to manage monogenean infections in intensive aquaculture with the greatest impact at the embryo stage.     

Beyond Symbiosis: Cleaner Shrimp Clean Up in Culture

Cleaner organisms exhibit a remarkable natural behaviour where they consume ectoparasites attached to “client” organisms. While this behaviour can be utilized as a natural method of parasitic disease control (or biocontrol), it is not known whether cleaner organisms can also limit reinfection from parasite eggs and larvae within the environment. Here we show that cleaner shrimp, Lysmata amboinensis, consume eggs and larvae of a harmful monogenean parasite, Neobenedenia sp., in aquaculture. Shrimp consumed parasite eggs under diurnal (63%) and nocturnal (14%) conditions as well as infectious larvae (oncomiracidia) diurnally (26%). Furthermore, we trialled the inclusion of cleaner shrimp for preventative parasite management of ornamental fish, Pseudanthias squamipinnis, and found shrimp reduced oncomiracidia infection success of host fish by half compared to controls (held without shrimp). Fish held without cleaner shrimp exhibited pigmentation changes as a result of infection, possibly indicative of a stress response. These results provide the first empirical evidence that cleaner organisms reduce parasite loads in the environment through non-symbiotic cleaning activities. Our research findings have relevance to aquaculture and the marine ornamental trade, where cleaner shrimp could be applied for prophylaxis and control of ectoparasite infections.     

Breeding biology aspects of spotted flapshell Turtle,Lissemys punctata (Lacepede 1788), in Bangladesh

This study was conducted to determine the breeding season, gonadal development, egg laying period, clutch size and other biological aspects of spotted flapshell turtle, Lissemys punctata, of Bangladesh between January 1997 and December 2001. The egg laying period of L. punctata, was found between August and March. The nesting sites were elevated fallow lands in secluded areas. The female turtle laid all the mature eggs at a time for each clutch at night. A gravid female turtle laid three clutches of eggs in each year and the mean clutch size was 13.0 ± 1.9 eggs and mean weight of each egg was 10.3 ± 1.3 g. The eggs are spherical in shape and whitish in color. The mean incubation period was 173 ± 34 days (range 119–225 days). The incubation period of first clutch was the longest than the second and third clutches. Hatching success was found 41%. Maximum hatching was observed in June. The present investigation was made to explore the possibility to raise turtle farming in captive condition. The findings would, hopefully, help to rear the species and to assess the commercial potentiality of turtle farming in captive condition, that is, in the eco-climatic condition of Bangladesh.     

Effect of Temperature on Pratylenchus penetrans Development

Reproduction and development of Pratylenchus penetrans were studied on genetically transformed ladino clover roots. Solitary females developing on transformed roots in nutrient gellan gum medium (pH 5.5) deposited 1.2, 1.5, 1.6, 1.8, and 2.0 eggs per day at the respective temperatures of 17, 20, 25, 27, and 30 °C. The number of eggs deposited was highly correlated with temperature. A reduction in egg-laying rates at the start of hatching was observed at all temperatures. Juvenile mortality was higher at 17 °C (50.4%), 20 °C (50.3%), and 30 °C (58.4%) than at 25 °C (34.6%) and 27 °C (37.6%). Life-cycle (egg deposition to egg deposition) duration was 46, 38, 28, 26, and 22 days at the respective temperatures. The developmental zero degrees (°C) and the effective accumulative temperatures (degree-days) required for hatching, female emergence, and onset of oviposition (completion of one generation) of P. penetrans were estimated to be 2.7 and 200, 4.2 and 548, and 5.1 and 564, respectively. Pratylenchus penetrans reproduces over a wide range of temperatures.     

Influence of Temperature on Multiplication and Egg Hatching of Longidorus africanus

Longidorus africanus multiplication on tomato was highest at 29 °C. Few nematodes were recovered after 6 weeks at soil temperatures of 35 °C or below 23 °C. The time to egg hatching was shortest and the percentage of eggs hatching was highest at 29 °C. The minimum temperature and the heat sum above this temperature required for egg development were calculated to be 14.3 °C and 94.08 degree-days, respectively. The thermal times required for egg development by L. africanus and L. elongatus were nearly identical. For both species the product of the base temperature and the heat sum was near constant, and at a temperature of 22.3 °C the rates of egg development were equal.     

Maternal Effects May Act as an Adaptation Mechanism for Copepods Facing pH and Temperature Changes

Acidification of the seas, caused by increased dissolution of CO₂ into surface water, and global warming challenge the adaptation mechanisms of marine organisms. In boreal coastal environments, temperature and pH vary greatly seasonally, but sometimes also rapidly within hours due to upwelling events. We studied if copepod zooplankton living in a fluctuating environment are tolerant to climate change effects predicted for 2100, i.e., a temperature increase of 3°C and a pH decrease of 0.4. Egg production of the copepod Acartia sp. was followed over five consecutive days at four temperature and pH conditions (17°C/ambient pH; 17°C/low pH; 20°C/ambient pH; 20°C/low pH). Egg production was higher in treatments with warmer temperature but the increase was smaller when copepods were simultaneously exposed to warmer temperature and lowered pH. To reveal if maternal effects are important in terms of adaptation to a changing environment, we conducted an egg transplantation experiment, where the produced eggs were moved to a different environment and egg hatching was monitored for three days. When pH changed between the egg production and hatching conditions, it resulted in lower hatching success, but the effect was diminished over the course of the experiment possibly due to improved maternal provisioning. Warmer egg production temperature induced a positive maternal effect and increased the egg hatching rate. Warmer hatching temperature resulted also in earlier hatching. However, the temperature effects appear to be dependent on the ambient sea temperature. Our preliminary results indicate that maternal effects are an important mechanism in the face of environmental change.     

A Single Hot Event That Does Not Affect Survival but Decreases Reproduction in the Diamondback Moth,Plutella xylostella

Extremely hot events (usually involving a few hours at extreme high temperatures in summer) are expected to increase in frequency in temperate regions under global warming. The impact of these events is generally overlooked in insect population prediction, since they are unlikely to cause widespread mortality, however reproduction may be affected by them. In this study, we examined such stress effects in the diamondback moth, Plutella xylostella. We simulated a single extreme hot day (maximum of 40°C lasting for 3, 4 or 5 h) increasingly experienced under field conditions. This event had no detrimental effects on immediate mortality, copulation duration, mating success, longevity or lifetime fecundity, but stressed females produced 21% (after 3 or 4 h) fewer hatched eggs because of a decline in the number and hatching success of eggs laid on the first two days. These negative effects on reproduction were no longer evident in the following days. Male heat exposure led to a similar but smaller effect on fertile egg production, and exposure extended pre-mating period in both sexes. Our results indicate that a single hot day can have detrimental effects on reproduction, particularly through maternal effects on egg hatching, and thereby influence the population dynamics of diamondback moth.     

Sequestration and Transfer of Cry Entomotoxin to the Eggs of a Predaceous Ladybird Beetle

In the past 10 years, sequestration of Cry toxins and transfer to offspring has been indicated in three insect species in laboratory studies. This work directly demonstrates the sequestration and intergenerational transfer of Cry1F by the parents of the aphidophagous coccinellid predator, Harmonia axyridis, to its offspring. Recently emerged adults (10 individual couples/cage/treatment) were exposed during 20 days to aphids (100 Myzus persicae each day) that fed on a holidic diet containing 20 μg/mL Cry1F (and a control-group). Egg batches and neonate larvae were monitored daily, and counted and weighed for immunodetection of Cry1F by ELISA. At the end of the bioassay, the parents were weighed and analyzed by ELISA. Cry1F was detected in the offspring, both eggs and neonate larvae, of exposed H. axyridis adults. On average the neonate larvae had 60% of the Cry1F concentration of the eggs from the same egg batch. The Cry1F concentration in the adults was positively correlated with the concentration in their eggs. These three results provided independent evidence of transfer to offspring. No detrimental effects of Cry1F were observed on the age of first reproduction, total number of eggs laid per female, age-specific fecundity, egg development time, hatching rate, or fertility rate. The occurrence and generality of intergenerational transfer of Cry toxins should be investigated in the field to determine its potential ecological implications.     

Effects of Eight Herbicides on In Vitro Hatching of Heterodera glycines

Laboratory studies were conducted to evaluate effects of selected herbicides on hatching of free eggs of the soybean cyst nematode, Heterodera glycines. The herbicides used were Atrazine (atrazine), Basagran (bentazon), Bladex (cyanazine), Blazer (acifluorfen), Command (clomazone), Lasso (alachlor), Sonalan (ethalfluralin), and Treflan (trifluralin). Treatments comprised two concentrations of commercial herbicide formulations and deionized water and 3.14 mM zinc sulfate as negative and positive controls, respectively. Eggs were extracted from females and cysts, surface disinfested, and incubated in herbicide or control solutions at 25 ± 2 C in darkness. Hatched second-stage juveniles were counted every other day for 24 days. Hatching of H. glycines eggs in 50 and 500 μg/ml Blazer was 42 to 67% less than that in deionized water and 6l to 78% less than that in zinc sulfate solution. Zinc sulfate significantly increased hatching activity in 50 μg/ml but not 500 μg/ml Blazer. The other herbicides tested at various concentrations had no significant effect on egg hatching. The specific component of Blazer inhibiting egg hatching is unknown. Suppression of hatching by Blazer indicates that this postemergence soybean herbicide may have a potential role in managing H. glycines.     

Alternative development in Polystoma gallieni (Platyhelminthes,Monogenea) and life cycle evolution

Considering the addition of intermediate transmission steps during life cycle evolution, developmental plasticity, canalization forces and inherited parental effect must be invoked to explain new host colonization. Unfortunately, there is a lack of experimental procedures and relevant models to explore the adaptive value of alternative developmental phenotypes during life cycle evolution. However, within the monogeneans that are characterized by a direct life cycle, an extension of the transmission strategy of amphibian parasites has been reported within species of Polystoma and Metapolystoma (Polyopisthocotylea; Polystomatidae). In this study, we tested whether the infection success of Polystoma gallieni within tadpoles of its specific host, the Stripeless Tree Frog Hyla meridionalis, differs depending on the parental origin of the oncomiracidium. An increase in the infection success of the parasitic larvae when exposed to the same experimental conditions as their parents was expected as an adaptive pattern of non-genetic inherited information. Twice as many parasites were actually recorded from tadpoles infected with oncomiracidia hatching from eggs of the bladder parental phenotype (1.63 ± 0.82 parasites per host) than from tadpoles infected with oncomiracidia hatching from eggs of the branchial parental phenotype (0.83 ± 0.64 parasites per host). Because in natural environments the alternation of the two phenotypes is likely to occur due to the ecology of its host, the differential infection success within young tadpoles could have an adaptive value that favors the parasite transmission over time.     

Differences in Hatching of Heterodera glycines Egg-mass and Encysted Eggs in vitro

Hatching studies with Heterodera glycines typically have been conducted with a mixture of egg-mass and encysted eggs. Laboratory research was conducted to compare hatching of H. glycines eggs from external egg masses with that of eggs extracted from within females and cysts (encysted eggs). Egg-mass eggs were collected by soaking infected soybean roots in 0.5% sodium hypochlorite, and encysted eggs were collected from females and cysts dislodged from the same roots with a stream of water. Eggs were incubated at 25 °C in deionized water, 3.0 mM ZnSO₄solution, or one of three synthetic H. glycines hatch inhibitors, mad hatched juveniles were counted every other day for 22 days. Samples of eggs collected at the beginning and end of all experiments were analyzed to determine extent of embryo development. Egg-mass eggs hatched more rapidly than encysted eggs during the first 16 days, but not thereafter. Throughout the experiments, hatch of egg-mass eggs in deionized water was greater than that of encysted eggs. From day 8 to day 22, egg-mass eggs were less sensitive than encysted eggs to the hatch inhibitor 2-(2''-carboxyethyl)-5-[carboxy(hydroxy)methylidenyl]cyclopentanone. A greater proportion of egg-mass eggs contained vermiform juveniles than did encysted eggs at the beginning of the experiments, but not at the end. Results indicated that H. glycines egg-mass and encysted eggs have different hatching behaviors that cannot be explained entirely by differences in embryological development.     

Relationship between the activity of the succinoxidase system and the rate of oxygen consumption during the embryonic development of the mealworm,Tenebrio molitor Linnaeus

1. Readings were made on the rates of oxygen consumption and on the activities of the succinoxidase system of eggs of the mealworm for each day of embryonic development at 30°C. 2. The rate of oxygen consumption, expressed as microliters/50 eggs/hour, was low (4.89) in newly laid eggs. It rose to 7.41 during the next 24 hours, remained at this level for the next 2 days, and then increased during the remainder of the embryonic period reaching a high value of 14.79 at the time of hatching. 3. The activity of cytochrome oxidase in eggs from newly emerged beetles, expressed as Δ log [Cy Fe⁺⁺]/minute, remained at a value of 0.042 during the first half of the embryonic period, increasing to 0.233 during the latter half of this period. 4. The activity of succinic dehydrogenase showed the same series of changes except at much lower values. Expressed as Δ log [Cy Fe⁺⁺⁺]/minute, they ranged from 0.010 in the newly laid egg to 0.034 at the end of the embryonic period. 5. The activity of cytochrome oxidase of the egg was found to decrease with parental age. Eggs from newly emerged beetles had activity values considerably higher than those of beetles 6 or 8 weeks after emergence. However, no comparable changes were noted in the activity of succinic dehydrogenase or in the rate of oxygen consumption. These observations suggest that cytochrome oxidase is not a rate-limiting enzyme in the respiratory metabolism of the mealworm egg.     

Effects of temperature on fecundity in vitro, egg hatching and reproductive development of Benedenia seriolae and Zeuxapta seriolae (Monogenea) parasitic on yellowtail kingfish Seriola lalandi

Globally, aquaculture industries involved with commercial culture of kingfish (Seriola spp.) experience outbreaks of monogenean parasites, which can cause heavy stock losses. In Australia and New Zealand, aquaculturists of kingfish Seriola lalandi incur financial losses caused by two monogenean species: Benedenia seriolae and Zeuxapta seriolae which parasitise the skin and gills, respectively. This study provides information on some basic temperature-dependent life-cycle parameters of these problematic monogeneans on S. lalandi. Hatching times and age at maturity were inversely related to water temperature within the range experienced by wild kingfish in New Zealand (13-21 degrees C). Mature B. seriolae in vitro laid on average 37 eggs/day that hatched over approximately 4 days; peak hatching occurred 9, 11 and 22 days post-deposition at temperatures of 21, 17.5 and 13+/-1.0 degrees C, respectively. Z. seriolae in vitro laid on average 246 eggs/day that hatched over 2 days; peak hatching occurred 7, 9 and 15 days post-deposition at these respective temperatures. B. seriolae matured within 20, 25 and 48 days p.i. at 21, 18 and 13 degrees C. Z. seriolae matured within 25, 37 and >52 days p.i. at the same temperatures. This research describes stages in the reproductive development of B. seriolae and Z. seriolae and discusses the inclusion of basic parasitic life-cycle parameters into management strategies designed to maximise treatment efficacy and limit monogenean epizootics in sea-cage kingfish culture.     

Ditylenchus dipsaci Infestation of Trifolium repens. I. Temperature Effects,Seedling Invasion,and a Field Survey

Rates of development of stem nematode (Ditylenchus dipsaci) in white clover (Trifolium repens) seedlings were found to be linearly related to temperature. Basal developmental temperature (T_b) was 3 °C, and the thermal constant (S) for development of gravid adult females from freshly laid eggs was 270 accumulated day-degrees above the T_b. Only 12% at 20 °C and 4% at 4 °C of the gravid female nematodes inoculated into seedling axils successfully penetrated seedling epidermis. These nematodes slowly migrated within the seedling and after a lag of 5 days at 20 °C started to lay eggs. The maximal rate of egg production was temperature-dependent, being 0.8 and 3.1 eggs female⁻¹ day⁻¹ at 10 and 20 °C, respectively. Nematodes emigrated rapidly from infested stolons when they were immersed in water, with rates being highest at 25 °C and lowest at 4 °C. The sensitivity to temperature of many of the parameters that govern nematode population dynamics indicates that climatic changes will have a marked effect upon this host-parasite system. A study of infested stolons from the field indicated that nematode numbers increased up to 3,000 or more before tissue senesence, triggered by nematode damage, caused a mass emigration of nematodes from the stolon.     

Observations on egg production in the monogenean Entobdella soleae

Egg production in the monogenean Entobdella soleae increases as adult parasites grow. Medium-sized adults (anterior hamulus length 550–600 μm; total body length approx. 5 mm) produced about 30 eggs per day at 12°C. Parasites with anterior hamuli exceeding 650 μm in length (total body length about 6 mm) may produce more than 60 eggs per day. In smaller adults, eggs tend to spend longer in the ootype after assembly of the shell and the ootype remains empty for longer periods of time. The time taken to assemble a single egg is relatively constant (4–6 min) in adults of all sizes and there is evidence of a small but significant increase in egg size as parasites increase in size. Some eggs were retained in the uterus for as long as 168 min but others spent less than 5 s in the uterus, indicating that the uterus is no more than a passageway for these eggs to the outside world. The egg cell (or zygote) precedes the vitelline cells as they progress along the ovo-vitelline duct to the ootype.     

The accelerating action of illumination in recovery of Arbacia eggs from exposure to ultraviolet radiation

Light of wave lengths 0.30µ to 0.50µ, accelerates return of the cleavage rate of Arbacia eggs to normal, after delay by exposure to ultraviolet radiation (wave lengths 0.238µ to 0.31µ). Recovery is apparently complete. Wave lengths 0.30µ to 0.50µ have no effect on the cleavage rate of normal eggs, nor does such illumination previous to dosage with ultraviolet radiation influence subsequent recovery. Acceleration of recovery of the egg occurs before fertilization as well as after. The effects of ultraviolet radiation and recovery therefrom are essentially the same in nucleated "white halves" as in the intact eggs. This phenomenon in the Arbacia egg seems basically comparable to photoreactivation of bacteria and fungi.     

Adaptive difference in daily timing of hatch in two locust species,Schistocerca gregaria and Locusta migratoria: The effects of thermocycles and phase polyphenism

This study examined the effects of temperature and phase polyphenism on egg hatching time in the desert locust, Schistocerca gregaria, and the migratory locust, Locusta migratoria. The two species exhibited differences and similarities in hatching behavior when exposed to different temperature conditions. In 12-h thermocycles of various temperatures, the S. gregaria eggs hatched during the cryoperiod (low temperature period), whereas L. migratoria eggs hatched during the thermoperiod (high temperature period). The eggs of both species hatched during the species-specific period of the thermoperiod in response to a temperature difference as small as 1 °C. Furthermore, the locusts adjusted hatching time to a new thermal environment that occurred shortly before the expected hatching time. In both species, the hatching of the eggs was synchronized to a specific time of the day, and two hatching peaks separated by approximately 1 day were observed at a constant temperature after the eggs were transferred from thermocycles 3 days before hatching. Eggs laid by gregarious females hatched earlier than those laid by solitarious females in S. gregaria but this difference was not observed in L. migratoria.     

Bemerkungen zur Biologie sowie Haltung und Vermehrung des Sokotra-Riesengeckos, Haemodracon riebeckii (Peters, 1882)

The Socotra Giant Gecko, Haemodracon riebeckii, is the largest species of lizard on Socotra Island. The nocturnal, arboreal and rupiculous living geckos are omnivorous. Two pairs were kept in terrariums and were fed with various insects (crickets, locusts, cockroaches), sweet fruits and other feeding stuff (such as meat, fish). Temporarily H. riebeckii was kept together with other lizards (Eublepharis macularius, Trachylepis socotrana), without any signs of aggressive behaviour. Juveniles and adults of both sexes are able to produce a sound. These acoustic signals seem to be related to predators, because never any intraspecific function could be observed. Within seven years of captive breeding two females produced 253 eggs. Usually two white and sticky soft-shelled eggs were laid within one clutch, more rarely a single egg was laid. The two eggs of a clutch were always laid on the same day. H. riebeckii belongs to the geckos that bury their eggs and practice some brood care, but no special parental care. The female is able to proof with her hind legs the deep and shape of a hollow in the substrate to bury the eggs, which were buried in a sticky and soft-shelled condition. They are oval in shape (egg length 16.4-19.8 mm, egg width 12.4-17.8 mm, quotient EL:EW 1.22±0.05) and have in the beginning a weight ranging from 1.7100 to 2.5201 g. As typical for geckos with hard-shelled eggs the egg weight decreases during the incubation period. The loss can be between 5.59 to 30.29%. The development of eggs up to hatching of young depends upon temperature and the germinal stage in the laid egg. The time difference between the hatching of the young within one clutch of two eggs was usually 1 to 5 days. In some cases there were, however, longer differences (up to 61 days), which are probably caused by different developmental stages of the embryos during the time of egg laying. The shortest incubation period recorded during our investigations was 83 days for eggs incubated at constant temperature of 28 to 29.5 °C and the longest 359 days at 26 to 26.5 °C. Constant high incubation temperatures caused a premature hatching of young. In normal hatched young were the yolk sac retracted and the navel closed. In premature hatched young were the yolk not resorbed and the mortality within the first three month comparatively high. The snout-vent length (SVL) of newly hatched young is from 27 to 39 mm and the tail length (TL) from 25 to 38 mm (SVL:TL index 0.90-1.27), the weight is from 0.7688 to 1.5366 g. Young specimens are distinguished from adults by the brown/white striped lower jaw and the white-banded tail. Young which hatched in the terrarium were eaten by the adults. A loss of young can be avoided if they are raised individually.     

Oviposition-Stimulant and Ovicidal Activities of Moringa oleifera Lectin on Aedes aegypti

Background

Natural insecticides against the vector mosquito Aedes aegypti have been the object of research due to their high level of eco-safety. The water-soluble Moringa oleifera lectin (WSMoL) is a larvicidal agent against A. aegypti. This work reports the effects of WSMoL on oviposition and egg hatching of A. aegypti.

Methodology/Principal Findings

WSMoL crude preparations (seed extract and 0–60 protein fraction), at 0.1 mg/mL protein concentration, did not affect oviposition, while A. aegypti gravid females laid their eggs preferentially (73%) in vessels containing isolated WSMoL (0.1 mg/mL), compared with vessels containing only distilled water (control). Volatile compounds were not detected in WSMoL preparation. The hatchability of fresh eggs deposited in the solutions in the oviposition assay was evaluated. The numbers of hatched larvae in seed extract, 0–60 protein fraction and WSMoL were 45±8.7 %, 20±11 % and 55±7.5 %, respectively, significantly (p<0.05) lower than in controls containing only distilled water (75–95%). Embryos were visualized inside fresh control eggs, but not within eggs that were laid and maintained in WSMoL solution. Ovicidal activity was also assessed using stored A. aegypti eggs. The protein concentrations able to reduce the hatching rate by 50% (EC50) were 0.32, 0.16 and 0.1 mg/mL for seed extract, 0–60 protein fraction and WSMoL, respectively. The absence of hatching of stored eggs treated with WSMoL at 0.3 mg/mL (EC99) after transfer to medium without lectin indicates that embryos within the eggs were killed by WSMoL. The reduction in hatching rate of A. aegypti was not linked to decrease in bacteria population.

Conclusions/Significance

WSMoL acted both as a chemical stimulant cue for ovipositing females and ovicidal agent at a given concentration. The oviposition-stimulant and ovicidal activities, combined with the previously reported larvicidal activity, make WSMoL a very interesting candidate in integrated A. aegypti control.     

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.