Stock Separation of Tenualosa Ilisha in Bangladesh Waters Using Parasites as Biological Tag

Fourteen species under eleven genus of endohelminths were identified from alimentary canal and associated organs of host, only two of them had satisfied the criteria of being as biological tag. These are one species of cestode parasite named Ilisha parthenogenetica and two acanthocephalan parasite species named Acanthocentis indica and Acanthocentis hilsai, which are in together termed as Acanthosentis spp. The presence of these parasites in all the habitats indicates host’s anadromous nature as well as higher prevalence of these tag parasites at respective sites and the trend of prevalence of infection in size class of host fish reinforced the belief that T. ilisha population in Bangladesh are largely anadromous in nature that cannot currently be divided into a group of discrete stocks and as a whole, a single stock of T. ilisha migrates from the sea to the rivers through the estuaries and vice versa. Asiat. Soc. Bangladesh, Sci. 46(1): 61-70, June 2020

Using parasites as biological tag for Hilsa shad (Tenualosa ilisha) migration in Bangladesh waters

The study was aimed at following the movement of adolescent Tenualosa ilisha from nursery grounds to feeding and spawning grounds or other type of movements in Bangladesh waters. To accomplish this, data on metazoan endoparasites were used as biological tags for detection of migratory route. A total of 2667 host fishes were collected from eleven sites covering the three different ecological habitats of Bangladesh. Initial selection of parasites as biological tags was executed by using established criteria, primarily on the basis of different level of infection in different habitats. The role of incidental parasites as tags is also discussed. Overall fourteen species under eleven genus of endohelminths were identified from alimentary canal and associated organs of host, only three species of them had satisfied the criteria of being as biological tag. These are cestode parasite Ilisha parthenogenetica and acanthocephalan parasite Acanthosentis indica and Acanthosentis hilsai. Higher prevalence of these parasites at respective sites and the trend of prevalence of infection in size class of host fish demonstrated host‟s anadromous nature and reinforced the belief that the T. ilisha as a whole, migrates from the sea to the rivers via the estuaries and vice versa. Bangladesh J. Zool. 48(2): 243-251, 2020

Effects of parasites upon non-host predator avoidance behaviour in native and invasive gammarids

The acanthocephalan parasite, Polymorphus minutus, manipulates its intermediate hosts' (gammarids) behaviour, presumably to facilitate its transmission to the definitive hosts. A fundamental question is whether this capability has evolved to target gammarids in general, or specifically sympatric gammarids. We assessed the responses to chemical cues from a non-host predator (the three-spined sticklebacks Gasterosteus aculeatus) in infected and non-infected gammarids; two native (Gammarus pulex and Gammarus fossarum), and one invasive (Echinogammarus berilloni) species, all sampled in the Paderborn Plateau (Germany). The level of predator avoidance was assessed by subjecting gammarids to choice experiments with the presence or absence of predator chemical cues. We did not detect any behavioural differences between uninfected and infected G. pulex and E. berilloni, but an elevated degree of predator avoidance in infected G. fossarum. Avoiding non-host predators may ultimately increase the probability of P. minutus' of predation by the definitive host. Our results suggested that P. minutus' ability to alter the host's behaviour may have evolved to specifically target sympatric gammarid host species. Uninfected gammarids did not appear to avoid the non-host predator chemical cues. Overall the results also opened the possibility that parasites may play a critical role in the success or failure of invasive species.

The invasive amphipod Gammarus tigrinus Sexton, 1939 conquering the north of Europe using a new pathway: the first recordings from Norway

The invasive amphipod Gammarus tigrinus has during the last decades spread to large parts of Northern Europe, mainly using pathways eastwards from The British Isles to Continental Europe and further northeast into the Baltic Sea. From the coastline it has to some extent spread further inland, especially in topographically low-relief landscapes with highly polluted rivers. This account reports another geographical direction of dispersal, towards north into Southern Norway. In coastal brackish-water regions G. tigrinus may displace other gammarids. Large parts of Norway consist of high-relief landscapes close to many estuaries, so the further spread into this country is doubtful. However, if the taxon can avoid the initial barriers using vectors and spread into new watercourses above such barriers and thrive in this new ambient water chemistry, it may have large negative influence on the other benthic fauna. But Norwegian lakes and rivers are most probably too electrolyte-poor to support this species. However, in estuaries and other brackish waters along the coast, at least in the southern part of Norway, the species will thrive. Gammarus tigrinus is the only known intermediate host for the native American acanthocephalan parasite Paratenuisentis ambiguus, which has the American eel as its main host. This parasite also infects the European eel, and this poses an additional threat to the already endangered eel in Norwegian rivers where G. tigrinus has been recorded.

Parasites of Prussian carp (Carassius gibelio): an invasive species in Alberta, Canada

A cyprinid, the Prussian carp (Carassius gibelio (Bloch, 1782)), has become an established invasive fish in several watersheds in Alberta, Canada. Originating in Eurasia, Prussian carp negatively impact native fish through predation, competition, and habitat modification. Prior to this study, nothing was known regarding the external and internal parasites of these fish in North America, although nine studies had been conducted in Europe and Asia. We examined 22 fish (20 female, 2 male) ranging from 3 to 5 years of age and recorded morphological features, stomach contents, and performed standard necropsy examinations for parasites. One parasite species, the acanthocephalan Pomphorhynchus bulbocolli Linkins in Van Cleave, 1919, was found in three fish (14%), with a mean intensity of 1.0. This is a new host record and the first report of any acanthocephalan parasite in Prussian carp. We conclude that Prussian carp are not introducing any novel parasites into native fish and that they are resistant to most infections by native parasites.

Parasite-induced colour alteration of intermediate hosts increases ingestion by suitable final host species

Parasites with complex life cycles often alter the phenotypic appearance of their intermediate hosts in order to facilitate ingestion by the final host. However, such manipulation can be costly as it might increase ingestion by less suitable or dead-end hosts as well. Species-specific parasitic manipulation is a way to enhance the transmission to suitable final hosts. Here, we experimentally show that the altered body colouration of the intermediate host Gammarus pulex caused by its acanthocephalan parasite Pomphorhynchus laevis differently affects predation by different fish species (barbel, perch, ruffe, brown trout and two populations of three-spined stickleback) depending on their suitability to act as final host. Species that were responsive to colour manipulation in a predation experiment were more susceptible to infection with P. laevis than unresponsive species. Furthermore, three-spined stickleback from different populations responded to parasite manipulation in opposite directions. Such increased ingestion of the intermediate host by preferred and suitable hosts suggests fine-tuned adaptive parasitic manipulation and sheds light on the ongoing evolutionary arms race between hosts and manipulative parasites.

Winning the arms race: host–parasite shared evolutionary history reduces infection risks in fish final hosts

Parasite manipulation of intermediate hosts evolves to increase parasite trophic transmission to final hosts, yet counter selection should act on the final host to reduce infection risk and costs. However, determining who wins this arms race and to what extent is challenging. Here, for the first time, comparative functional response analysis quantified final host consumption patterns with respect to intermediate host parasite status. Experiments used two evolutionarily experienced fish hosts and two naive hosts, and their amphipod intermediate hosts of the acanthocephalan parasite Pomphorhynchus tereticollis . The two experienced fish consumed significantly fewer infected than non-infected prey, with lower attack rates and higher handling times towards the former. Conversely, the two naive fish consumed similar numbers of infected and non-infected prey at most densities, with similar attack rates and handling times towards both. Thus, evolutionarily experienced final hosts can reduce their infection risks and costs via reduced intermediate host consumption, with this not apparent in naive hosts.

Sclerocollum saudii Al-Jahdali, 2010 (Acanthocephala: Cavisomidae) as a sentinel for heavy-metal pollution in the Red Sea

Currently, fish helminth parasites, especially cestodes and acanthocephalans, are regarded as sentinel organisms to elucidate metal pollution in aquatic ecosystems. Here, 34 specimens of the fish Siganus rivulatus were collected in the Red Sea, from a seriously polluted, small lagoon named Sharm-Elmaya Bay, at Sharm El-Sheikh, South Sinai, Egypt; 22 (64.7%) were infected by Sclerocollum saudii (Acanthocephala: Cavisomidae). Thus, 22 natural infrapopulations (26–245 individuals) of this parasite were collected from infected fish. Samples of water and sediments from the bay, samples of muscle, intestine and liver from each fish, and samples from the parasite were taken for analysis of heavy metals (cadmium (Cd) and lead (Pb)). Both Cd and Pb concentrations in sediments were higher than those in water. The concentration of these metals were significantly higher in tissues (intestine, liver and muscle) of non-infected fish than those in infected fish, with Pb concentrations consistently higher than those of Cd, and both were drastically decreased in the order: liver > intestine > muscle. Metal concentrations in this acanthocephalan were much higher than those in its fish host. There were strong negative relationships between metal concentrations in tissues (intestine, liver and muscle) of infected fish and infrapopulation size, and between metal concentrations in the acanthocephalan and its infrapopulation size. These relationships strongly suggest competition for these metals between the fish host and its acanthocephalan parasite, and intraspecific competition among acanthocephalan individuals for available metals in the fish intestine. Bioconcentration factors were relatively high, since the mean Cd concentration in S. saudii was 239, 68 and 329 times higher than those in intestine, liver and muscle tissues, respectively, of its fish host. Also, mean Pb concentration was 55, 13 and 289 times higher than those in these tissues, respectively. The host–parasite system described here seems to be promising for biomonitoring of metal pollution in the Red Sea.

Remarkable differences in the presence of the acanthocephalan parasite Echinorhynchus truttae in brown trout (Salmo trutta) captured in two adjacent river basins in Galicia (NW Spain)

This is the first report on the presence of acanthocephalan parasite Echinorhynchus truttae in brown trout (Salmo trutta) from Spain. A total of 343 fish were captured by local anglers from 19 rivers in the adjacent Tambre and Ulla watersheds in Galicia (north-western Spain). Macroscopic and microscopic analyses of the intestinal contents revealed the presence of adults and/or eggs of E. truttae in 53 of the 123 trout from Tambre river basin (43.1%). By contrast, parasitic forms of this acanthocephalan were only observed in eight of the 220 fish from Ulla basin (3.6%), showing significant differences between the prevalences obtained in two adjacent watersheds (P < 0.001, odds ratio 19.0). Prevalence was significantly higher in specimens >3 years (length >26.0 cm) than in younger specimens (P < 0.05). The absence of Gammarus pulex in the region suggests that native gammarid species in Galicia (Echinogammarus lusitanicus and Echinogammarus beriyoni) may act as intermediate host in the life cycle of E. truttae. Different prevalences of E. truttae indicate that the presence/abundance of the intermediate crustacean host may be different in the two river basins, probably as a consequence of various abiotic factors and anthropogenic activities.