Occurrence of Infestation with the Isopod, Alitropus Typus M. Edwards (Crustacea: Flabellifera: Aegidae) on Commercially Important Freshwater Fishes of Kerala, India

Rapidly rising temperatures and increasing organic load in the inland and coastal waters has led to a significant increase in parasite population. The isopod Alitropus typus infestation on fish in these waters have become more frequent, causing mortalities in both wild and cultured fishes. The present study was aimed to investigate the infestation on different fish hosts, mean intensity, prevalence, environmental influences on the parasite abundance and the histopathological changes it causes in the host. A total of 219 isopod specimens were collected from 149 infested fishes in two districts of Kerala, India. Among the different fish hosts, Channa striata was found to be the most susceptible, followed by Catla catla, Cyprinus carpio, and Wallago attu, with 81%, 10%, 7%, and 2% occurrence, respectively. The prevalence and mean intensity of infestation were found to be 69.8%, 44.4%, 68.2%, 62.5% and 1.33, 4.25, 1.26, 1.80 in C. striata, W. attu, C. catla, and C. carpio, respectively. The parasite abundance was directly influenced by temperature and rainfall patterns. The histopathology of affected gill tissues showed epithelial lifting, rupture of secondary gill filaments, vacuole formation and hemocytic infiltration. The findings indicated that the isopod parasite, A. typus had a negative impact on fish health and appearance, causing economic losses to the small scale farmers/fishermen. This is the first reported record of the infestation of isopod parasite, A. typus on the Indian major carp C. catla and C. carpio from India.

Evolution of diverse host infection mechanisms delineates an adaptive radiation of lampsiline freshwater mussels centered on their larval ecology

North American watersheds contain a high diversity of freshwater mussels (Unionoida). During the long-lived, benthic phase of their life cycle, up to 40 species can co-occur in a single riffle and there is typically little evidence for major differences in their feeding ecology or microhabitat partitioning. In contrast, their brief parasitic larval phase involves the infection of a wide diversity of fish hosts and female mussels have evolved a spectrum of adaptations for infecting host fish with their offspring. Many species use a passive broadcast strategy: placing high numbers of larvae in the water column and relying on chance encounters with potential hosts. Many other species, including most members of the Lampsilini, have a proactive strategy that entails the use of prey-mimetic lures to change the behavior of the hosts, i.e., eliciting a feeding response through which they become infected. Two main lure types are collectively produced: mantle tissue lures (on the female’s body) and brood lures, containing infective larvae, that are released into the external environment. In this study, we used a phylogenomic approach (ddRAD-seq) to place the diversity of infection strategies used by 54 North American lampsiline mussels into an evolutionary context. Ancestral state reconstruction recovered evidence for the early evolution of mantle lures in this clade, with brood lures and broadcast infection strategies both being independently derived twice. The most common infection strategy, occurring in our largest ingroup clade, is a mixed one in which mimetic mantle lures are apparently the predominant infection mechanism, but gravid females also release simple, non-mimetic brood lures at the end of the season. This mixed infection strategy clade shows some evidence of an increase in diversification rate and most members use centrarchids (Micropterus & Lepomis spp.) as their predominant fish hosts. Broad linkage between infection strategies and predominant fish host genera is also seen in other lampsiline clades: worm-like mantle lures of Toxolasma spp. with sunfish (Lepomis spp.); insect larvae-like brood lures (Ptychobranchus spp.), or mantle lures (Medionidus spp., Obovaria spp.), or mantle lures combined with host capture (Epioblasma spp.) with a spectrum of darter (Etheostoma & Percina spp.) and sculpin (Cottus spp.) hosts, and tethered brood lures (Hamiota spp.) with bass (Micropterus spp.). Our phylogenetic results confirm that discrete lampsiline mussel clades exhibit considerable specialization in the primary fish host clades their larvae parasitize, and in the host infection strategies they employ to do so. They are also consistent with the hypothesis that larval resource partitioning of fish hosts is an important factor in maintaining species diversity in mussel assemblages. We conclude that, taking their larval ecology and host-infection mechanisms into account, lampsiline mussels may be legitimately viewed as an adaptive radiation.

Prevalence of Cymothoidae (Isopoda) Infestation in Bigeye Scad (Selar crumenophtalmus) from Batangas, Philippines

Cymothoid isopod research is relatively scarce in the Philippines, despite the local economic significance of bigeye scad as an inexpensive source of protein and other nutrients. Isopod parasitism has also been shown to have detrimental effects on their fish hosts. The current study aimed to define the host-parasite relationship between cymothoid isopod and bigeye scad by determining cymothoid isopod prevalence, intensity, and host-parasite length correlations in bigeye scad (Selar crumenophthalmus) hosts sourced from Batangas, Philippines. Fish samples were sampled from the Tagaytay City Market in Cavite, which sources fish directly from Batangas. Fish samples were immediately measured and inspected for isopods in the branchial and buccal cavities. Isopods found were extracted, measured, and preserved in ethanol for identification. The isopods were identified as cymothoid isopods and consisted mostly of Norileca indica specimens and one Glossobius impressus. Prevalence and mean intensity of cymothoid isopod infections in bigeye scad were 30% and 1.6, respectively. A possible correlation between isopod size and host size was speculated for non-ovigerous female isopods, but data for male and ovigerous female isopod specimens were inconclusive. The host-parasite size relationships between bigeye scad and isopods are less likely based on body size of either the host or the parasite and are more likely based on other factors such as host cavity size.

Occurrence of Neoechinorhynchus curemai (Acanthocephala: Neoechinorhynchidae) in Prochilodus nigricans (Characiformes: Prochilodontidae), in southwestern Amazon

Prochilodus nigricans is extensively exploited in fishing and aquaculture activities in the Brazilian Amazon, it is the definitive host for Neoechinorhynchus curemai Noronha, 1973. Thus, the present study aimed to evaluate the occurrence of N. curemai in P. nigricans and the parasite-host relationship in three rivers (Juruá, Crôa and Môa) in the municipality of Cruzeiro do Sul, state of Acre, Brazil. Fish were caught, weighed, measured, and subjected to necropsy, and the gastrointestinal tract and viscera were analyzed. A total of 178 specimens of N. curemai were found in 61 infected fish, with the (p= 58.62%). The prevalence, mean intensity, and mean abundance were higher in hosts from the Môa River, and lower from the Juruá River. Regarding the length-weight relationship, the b-value did not differ statistically from three (b=3) for fish species in the three locations, nor in parasitized and non-parasitized species. In addition, growth was considered isometric, and in the case of the relative condition factor, there was no difference in fish hosts between the three rivers. The correlation between parasite intensity, condition factor, length, and weight of P. nigricans was not significant. Thus, this parasite infestation varied between the habitats. However, this did not influence the growth and development of the hosts.

Acanthocephalan Worms Mitigate the Harmful Impacts of Heavy Metal Pollution on Their Fish Hosts

Toxic metal pollutants in aquatic environments and infestationwith intestinal helminths adversely affect the fish health, as well as fish consumers. Acanthocephalan worms in fish intestine have a high potential to absorb and bioaccumulate different heavy metals, especially toxic ones, from the intestine via their tegument with greater efficiency than the fish intestinal wall. Herein, 47 specimens of the fish Siganusrivulatus were trapped in the Red Sea, Egypt, from a chronically polluted bay. All were intoxicatedwith Cd and Pb; 20 (42.5%) were uninfected with any intestinal worm, but the other 27 (57.5%) were infected only by the intestinal acanthocephalan Sclerocollum rubrimaris. The number of individual worms in a fish host (infrapopulation size) ranged from 32 to 236. As a reference group, 22 uncontaminated–uninfected specimens of S. rivulatus were trapped from a small unpolluted bay. Our results revealed that infection with acanthocephalans alleviatesthe harmful effectsof toxic metalson their fish hosts by: (1) lowering the elevated concentrations of both Cd and Pb in fish liver; (2) lowering the elevated levels of liver enzymes (ALT, AST, ALP, and GGT), glucose, triglycerides, and urea in fish blood serum; and (3) raising the declined levels of total protein and albumin in fish blood serum. All of these were dependent on S. rubrimaris infrapopulation size in fish intestine.

Checklist of Fish Hosts of Species of Contracaecum Railliet & Henry, 1912 (Nematoda: Ascaridida: Anisakidae) in Iraq

Surveying literature concerning the occurrence of the nematode larval forms of the genus Contracaecum in fishes of Iraq, showed the infection of 44 freshwater and marine fish species in Iraq with such larvae. The infection included larvae of unidentified Contracaecum species, Contracaecum rudolphii type-B and Contracaecum septentrionale Kreis, 1955. The infections were distributed in Tigris, Euphrates and Shatt Al-Arab rivers as well as some of their tributaries, lakes, marshes, drainage networks in addition to many fish ponds and floating cages in different parts of Iraq. This checklist also provided references on some histopathological and biochemical changes, some ecological aspects of the infection, life cycle and scanning electron microscopy. In addition, this checklist includes literature on six species of adult Contracaecum species as well some unidentified species of this genus from 17 bird species from different parts of Iraq, of which both Eurasian bittern Botaurus stellaris and pygmy cormorant Microcarbo pygmaeus were infected with a maximum number of three Contracaecum species as well as unidentified species of this genus.