Swimming performance of silver eels is severely impaired by the swim-bladder parasite Anguillicola crassus (original) (raw)
Related papers
Journal of Parasitology, 2012
The introduced parasite Anguillicoloides crassus is thought to play an important role in the decline of freshwater eel (Anguilla spp.) populations. These nematodes are known to negatively affect many fitness-related traits in eels. We used experimental infections to study the effect of A. crassus on the relative size or mass of organs, and the expression of functionally relevant genes (total of 12 parameters) that are involved in the silvering process of Anguilla anguilla. Our results showed that the liver mass, the hemoglobin a-chain, and androgen receptors a expression levels were significantly higher in infected eels, whereas the freshwater rod opsin expression level and the gut mass were significantly lower in infected eels. Our results suggested that infected eels were at a more advanced stage in the silvering process than uninfected counterparts of similar size. These results may be explained by 2 hypotheses. First, A. crassus could trigger physiological mechanisms involved in the silvering process as a side-effect of infection. Second, eels may adjust their life history traits in response to infection. The implications for eel migration and reproductive success may be either negative or positive, depending on whether the response to A. crassus infection results in an additional cost of the parasite or is due to the phenotypic plasticity of the host.
Influence of introduced vs. native parasites on the body condition of migrant silver eels
Parasite, 2013
Because parasitism is among the reasons invoked to explain the collapse of Anguilla anguilla, we evaluated the parasitic constraint on body condition (BC) of migrant silver eels as a proxy of fitness with inter-site comparisons. Metazoan parasites were studied in 149 silver eels from five sites (northern Europe). In total, 89% were infected by 13 species including Myxozoa, Monogenea, Cestoda, Nematoda, and Acanthocephala. Anguillicoloides crassus was most common (56%), then Acanthocephalus clavula (30%), and Pseudodactylogyrus sp. (17%). BC, calculated for 58 females, was negatively correlated by abundance of the introduced Pseudodactylogyrus sp. but not by other parasite taxa. Nevertheless, the introduced A. crassus was considered as a severe pathogen based on previous data, whereas the native A. clavula was supposed to have limited impact. Parasite component communities and BC were different between sites. Silver eels from Stockholm Archipelago (Sweden) were the least parasitized (40% vs. 90-95% for other sites) with no parasites on the gills. Burrishoole (Ireland) differed by the absence of A. crassus and high prevalence of A. clavula (84%) but without consequences on BC. Gudenaa (Denmark), Corrib (Ireland), and Frémur (France) were close due to high prevalence of A. crassus (89-93%). Gudenaa and Corrib were the most similar because Pseudodactylogyrus sp. was also highly prevalent (respectively 71% and 60%) whereas absent in Frémur. Our results suggest that the fitness loss induced by the introduced parasites could affect the spawning success of migrant silver eels from Gudenaa and Corrib, and to a lesser extent from Frémur, but probably not those from Stockholm Archipelago and Burrishoole.
While there have many numerous studies regarding the spread of the nematode Anguillicoloides crassus in its host, few of these have addressed the pathology itself. In the present work, we examined the status of the swim bladders of European eels populating Lake Oubeïra, by assessment of their Swim bladder Degenerative Index (SDI). We found that the 450 eels that we captured were aged between 19 and 79 months, and that they exhibited an extremely fast growth rate. Our assessment of the REPRODUCTIVE capacity of the European EELs (EELREP) [13] revealed that 3.78% had not undergone sexual differentiation, while 95.78% were females, of which more than half were silvered; and only 0.45% were silvered males. The parasitism by Anguillicoloides crassus exhibited the following epidemiological parameters: P=50.44%, I=7.04±3.18 parasites per swim bladder, and A=3.74±2.04 parasites per eel (the latter varies significantly with the SDI). Lastly, we noticed that 95% of the examined swim bladders w...
2016
While there have many numerous studies regarding the spread of the nematode Anguillicoloides crassus in its host, few of these have addressed the pathology itself. In the present work, we examined the status of the swim bladders of European eels populating Lake Oubeïra, by assessment of their Swim bladder Degenerative Index (SDI). We found that the 450 eels that we captured were aged between 19 and 79 months, and that they exhibited an extremely fast growth rate. Our assessment of the REPRODUCTIVE capacity of the European EELs (EELREP) [13] revealed that 3.78% had not undergone sexual differentiation, while 95.78% were females, of which more than half were silvered; and only 0.45% were silvered males. The parasitism by Anguillicoloides crassus exhibited the following epidemiological parameters: P=50.44%, I=7.04±3.18 parasites per swim bladder, and A=3.74±2.04 parasites per eel (the latter varies significantly with the SDI). Lastly, we noticed that 95% of the examined swim bladders w...
Journal of fish biology, 2015
The effect of Anguillicola crassus, Pseudodactylogyrus bini and Pseudodactylogyrus anguillae infection on the behaviour of downstream migrating adult European eels Anguilla anguilla as they encountered accelerating water velocity, common at engineered structures where flow is constricted (e.g. weirs and bypass systems), was evaluated in an experimental flume. The probability of reacting to, and rejecting, the velocity gradient was positively related to A. crassus larval, adult and total abundance. High abundance of Pseudodactylogyrus spp. reduced this effect, but A. crassus was the strongest parasitic factor associated with fish behaviour, and abundance was positively related to delay in downstream passage. Delayed downstream migration at hydraulic gradients associated with riverine anthropogenic structures could result in additional energetic expenditure for migrating A. anguilla already challenged by A. crassus infection.
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2008
A swimming speed of 0.4 meters per second (m s − 1 ) is the minimal speed for European female silver eels to reach the spawning sites in the Sargasso Sea in time. As silver eels cease feeding when they start their oceanic migration, the cost of transport (COT) should be minimised and the swimming speed optimised to attain the highest energetic efficiency. In this study, we have investigated the optimal swimming speed (U opt ) of silver eels since U opt may be higher than the minimal swimming speed and is more likely to resemble the actual cruise speed. A variety of swimming tests were performed to compare endurance swimming between farmed eels and wild eels, both in freshwater and in seawater. The swimming tests were run with 101 silver female eels (60-96 cm, 400-1500 g) in 22 Blazka-type swim tunnels in a climatised room at 18°C with running freshwater or seawater. Tests were run at 0.5-1.0 m s − 1 with increments of 0.1 m s − 1 , and either 2 h or 12 h intervals. Remarkably, both tests revealed no changes in oxygen consumption (M .
Impact of Eel Viruses on Recruitment of European Eel
2008
Eels have an uncommon catadromic life cycle with exceptional migratory patterns to their spawning grounds several thousand kilometres away: the European eel (Anguilla anguilla) travels over 5,500 km to the Sargasso Sea (Schmidt 1923; McCleave and Kleckner 1987; Tesch 1982; Tesch and Wegner 1990); the American eel (A. rostrata) migrates over 4,000 km also to the Sargasso Sea (Castonguay and McCleave 1987; McCleave and Kleckner 1987; Tesch and Wegner 1990); the Australian eel (A. aus-tralis) travels over 5,000 km into the Pacific Ocean to spawn (Jellyman 1987); and the Japanese eel (A. japonica) travels over 4,000 km to an area near the Marianna Islands in the Philippines to spawn (Tsukamoto 1992). Evidently such long distance swimming will place those fishes under extra stress caused by the long starvation period, the high energy cost of the journey, and the many changes in the environment such as salt water, darkness, high pressure, and low temperatures, among other stress factors. Stress is often a basis for disease in eel, especially in intensive eel culture (Haenen and Engelsma, 2005 unpublished finding). Nowadays, global transport of live fishes for aquaculture has facilitated the global spread of pathogens from diseased to healthy stocks. Within the last few decades, aquaculture has become an important production branch in our society. Its global production has more than doubled between 1986 and 1996 in tonnage and value, and over one quarter of human fish consumption at world scale is now produced in aquaculture (Naylor et al. 2000). The Netherlands is one of the leading eel producing & trading countries (Heinsbroek and Kamstra 1995). Blanc (1997) showed that nearly 100 pathogens have been introduced into European water bodies since the introduction of aquaculture. Worldwide many diseases are known in both wild and cultured eel. Parasites, for example trematodes, Anguillicola crassus(nematode), and Myxidium giardi (myxosporean)occur naturally in wild eel populations, mostly in low numbers, without causing mortality (Køie 1988; Van Banning and Haenen 1990; Borgsteede et al. 1999). However, under culture conditions, with eels kept in high densities, they may be harmful. Eel pathogenic bacteria like Vibrio vulnificus, Vibrio anguillarum, Pseudomonas anguillisepticaand Edwardsiella tardamay also cause disease, especially when a stress factor is involved or when the eel is injured (Veenstra et al. 1993; Austin and Austin 1999; Haenen and Davidse 2001). As far as we know, the clinical signs are often more severe under culture conditions compared to in the wild.
Bulletin Français de la Pêche et de la Pisciculture, 2003
We have investigated the spread of the infection by Anguillicola crassus among the silver phase of the European eel Anguilla anguilla in the Rhône delta. We reported values of prevalence, mean intensity and abundance in 4 habitats and we revealed negative relationships between these parasitic parameters and values of salinity (prevalence from 52 % in brackish waters to 77 % in fresh waters). We have also assessed the health state of the infected organ, i.e. the swimbladder. This may be a way to check the parasitic history of individuals throughout their continental phase. In silver eels free from parasites, the proportion of past infected individuals was ranged between 40 % and 78 %. When adding individuals showing worms at the autopsy with those showing signs of past infection(s), we highlighted a great proportion of silver eels really affected by anguillicolosis (from 71 % to 95 %, with a negative relationship in respect to salinity values). So, considering the spread of the infection, and its potential impairments on body condition, gas exchanges, hydrostatic abilities, etc., one may legitimately question about the proportion of silver eels that may get back to the Sargasso sea and reproduce.
Aquatic Biology, 2009
Freshwater habitat use by yellow-stage eels is facultative. Survival, infestation rates, and prevalence of the swimbladder parasite Anguillicola crassus (Nematoda) in European eel is higher in freshwater than in brackish water or seawater. This suggests that infestation patterns vary among habitats with different salinity. To evaluate whether Japanese eel Anguilla japonica populations with different habitat use behavior have different parasite dispersion modes, we examined by electron probe microanalyzer the otolith strontium:calcium (Sr:Ca) ratios of 166 Japanese eels collected from the Kaoping River, southwestern Taiwan, in 2006 and 2007. According to the mean and SD of otolith Sr:Ca ratios, we differentiated between 3 types of habitat use in eels: freshwater, low-migratory (Type 1), brackish water, low-migratory (Type 2), and high-migratory (Type 3). The mean prevalence of A. crassus was lowest in Type 2, intermediate in Type 1, and highest in Type 3, but there were no significant differences. Mean intensity of A. crassus at the larval stage (but not adult stage) was significantly higher for Type 1 than for the other 2 types. Our results suggest that diverse habitat use by Japanese eels implies behavioral plasticity to make use of different ecological niches. High-migratory Type 3 eels, which dominate the population, may serve as vectors disseminating A. crassus among different habitats.
Fish Physiology and Biochemistry, 2011
The onset of downstream migration of European eels is accompanied by a cessation of feeding and the start of sexual maturation which stresses the link between metabolism and sexual maturation, also suggesting an important role for exercise. Exercise has been tested with eels in swim tunnels and was found to stimulate the onset of sexual maturation. In this study, we have investigated the interplay between migration and maturation in the field during the downstream migration of female silver eels. Temporal changes in migratory status and sexual maturation among silver eels of the upstream Rhine River system over 3 months of the migration season (August, September and October) were determined in biometrical parameters, plasma 17b-estradiol and calcium levels, oocyte histology and gonadal fat levels. Furthermore, the ecological relevant parameters age as determined by otolithometry and health aspects indicated by haematocrit, haemoglobin and swim-bladder parasite load were measured. Silver eels were estimated to be 14 years old. A strong temporal progression in migratory stage was shown over the months of downstream migration. Catches probably represented a mix of reproductive migrants and feeding migrants of which the ratio increased over time. Furthermore, this study confirmed our hypothesis linking the migratory stage to early maturation as indicated by enlargement of the eyes, oocyte growth and fat deposition in the oocytes, exactly the same changes as found induced by exercise but not ruling out environmental influences. Migrants show extensive fat uptake by the oocytes, probably stimulated by the swimming exercise. In addition, at least 83% of the silver eels in this spawning run may have suffered from negative effects of swim-bladder parasites on their swimming performance.