Hysterothylacium patagonense n. sp. (Nematoda: Anisakidae) from freshwater fishes in Patagonia, Argentina, with a key to the species of Hysterothylacium in American freshwater fishes

A regional scale study of parasites in Percichthys trucha, an endemic fish of southern South America: insights on diversity and distribution from two decades of field surveys

The current conservation status of Percichthys trucha (Creole perch) is Least Concern, although the population trend is considered to be decreasing. We conducted an extensive survey of parasite fauna in this species over two decades in its distribution range in Argentina. Fish were collected using gill and trawl nets. Parasites were collected, identified, and counted to calculate prevalence and mean intensity. The present work reports the parasite species infecting P. trucha, using data from our own survey and from previously published records. This information enables us to evaluate infection and distribution patterns, assess the role of P. trucha as host, determine the specificity of the parasites, and evaluate the threat represented by introduced, invasive parasites. The data set consists of a total of 453 host-parasite-locality records, of which only 15 are exclusively bibliographic. We found 44 parasite taxa: 19 digeneans, 4 monogeneans, 5 cestodes, 8 nematodes, 4 acanthocephalans, 3 crustaceans, and 1 mollusk. The most represented families were Diplostomidae, Heterophyidae, and Dactylogyridae. This study increases the number of parasite species known from 25 to 44. It can be concluded that this parasite fauna is characterized by high diversity, particularly of digeneans, and most of the parasites reproduce within this host, a pattern which is related to the top position of this fish species in the trophic webs. Six parasite species (Allocreadium patagonicum, Homalometron papilliferum, Acanthostomoides apophalliformis, Duplaccessorius andinus, Pseudodelphys limnicola, and Hysterothylacium patagonense) exhibit high host specificity (only matures in Creole perches) and are widely distributed, which could now be considered as "biogeographical core helminth fauna." Some P. trucha populations are affected by the invasion of alien fishes like Cyprinus carpio and pathogenic parasites like Lernaea cyprinacea and Schizocotyle acheilognathi. Our findings emphasize the need for further research.

Diversity and Ecology of Endohelminth Parasites in a Fish Assemblage of an Amazon River Tributary in Brazil

PURPOSE

This study investigated the diversity and ecology of endohelminth parasites in an assemblage of 15 omnivorous and four piscivorous fish species in a tributary of the Amazon River (Brazil).

METHODS

Fish were collected bimonthly to evaluate the diversity and ecology of endohelminth parasites in omnivorous and piscivorous fish species in a tributary of the Amazon River using traditional methods and other methods.

RESULTS

A total of 4,234 parasites of 19 species (8 Nematoda, 5 Acanthocephala, 4 Digenea and 2 Cestoda) were sampled from 531 fish specimens. Procamallanus (Spirocamallanus) inopinatus and Contracaecum sp. were the predominant parasite species, and the parasites showed an aggregated dispersion pattern. Positive correlation was shown between the abundance of Contracaecum sp., Hysterothylacium patagonense and P. (S.) inopinatus, and the body size of 15.8% of the host fish examined. No difference was shown for Shannon diversity index and evenness between omnivorous and piscivorous hosts, but the richness, abundance and intensity of parasites were greater in piscivorous host fish.

CONCLUSION

In the fish assemblage, the presence of parasites in the larval and adult stages suggests that these are intermediate, paratenic and definitive hosts, reflecting the feeding habits of the omnivorous and piscivorous host species. 74.1% of the parasite species were new records for the different host species examined. The size of the hosts, trophic level and diet had an influence on the structuring of endohelminth communities and infracommunities.

Variation in Helminth Parasite Component Communities of Gambusia affinis

In north-central Texas streams, seasonal changes in ambient temperature and rainfall result in dynamic variation in microhabitat structure, affecting the distribution and abundance of hosts. Since the complex life cycles of parasites require the presence and interaction of multiple hosts, the seasonal variations in microhabitats could influence parasite component communities within these ecosystems. Gambusia affinis (western mosquitofish) serves as a host for a variety of larval and adult parasites. Factors that affect helminth component communities in populations of mosquitofish from the Paluxy River were investigated in this study. Gambusia affinis individuals were collected from 3 sites monthly from June 2015 through August 2016. All helminth parasites were collected during necropsy and subsequently identified. From 495 mosquitofish, 5,283 helminths were collected. Component community diversity varied among collection sites and collection dates and was positively influenced by river flow. These results indicate that helminth assemblages infecting mosquitofish in the Paluxy River vary through time and space, as well as in response to environmental variation (i.e., changes in water flow).

Morphometric and molecular descriptions of three new species of Hysterothylacium (Nematoda: Raphidascarididae) from Australian marine fish

Three new species of Hysterothylacium Ward & Magath, 1917, including H. australe, H. kajikiae and H. brucei, from Australian marine fish are described and illustrated by light microscopy followed by genetic characterization of their first and second internal transcribed spacers (ITS-1 and ITS-2, respectively). This is the first study reporting ITS sequence data for adult Hysterothylacium spp. in Australia, which provides an insight into the identification of some of the Hysterothylacium larval types. Alignment of ITS sequences of these species with Hysterothylacium larval types previously reported in Australia showed that fourth-stage Hysterothylacium larval type XI from Seriola lalandi and third-stage Hysterothylacium larval type X from Sphyraene novae-hollandiae are identical with ITS sequences of H. australe, suggesting that these fish are natural intermediate/paratenic hosts of H. australe.

A new species of Hysterothylacium (Nematoda: Anisakidae) parasite of Ariopsis guatemalensis (Osteichthyes: Ariidae) from Tres Palos lagoon, Mexico

Hysterothylacium perezi n. sp. is described from the intestine of the "cuatete" Ariopsis guatemalensis Günther, 1864 (Osteichthyes: Ariidae), in Tres Palos, a coastal lagoon located in the Mexican Pacific basin. The new species differs from all other species of Hysterothylacium Ward and Magath, 1917, in possessing a spinous postcloacal pad. In addition, H. perezi is readily distinguished from the 21 species described in fishes from America and Hawaii by having the greatest number of caudal papillae (47 to 51 pairs + 1 single, precloacal papillae). This species is the third described from hosts inhabiting estuarine environments in America and the fourth reported in Mexico.

Hysterothylacium winteri sp. n. (Nematoda: Anisakidae), a parasite of Chilean rock cod, Eleginops maclovinus (Perciformes: Eleginopidae), from South Chile

Hysterothylacium winteri sp. n. (Nematoda: Anisakidae) was collected from the intestine of a marine-estuarine fish, Eleginops maclovinus (Valenciennes) (Perciformes: Eleginopsidae), from Abtao in the Gulf of Ancud, Chile. Sixteen (51.6%) out of 31 fish were infected; the intensity was 1-10 (mean 4) worms/host. The new species belongs to the group of congeners possessing one double pair of postanal papillae. By possessing a lateral pair of phasmids situated near the tip of tail, H. winteri most closely resembles Hysterothylacium habena. The new species can be distinguished by the lip flanges forming broadly rounded points and the equal, short spicules (320-400 microm long) representing 0.9-1.7% of body length.

On a new species of Hysterothylacium (Nematoda: Anisakidae) from Cauque mauleanum (Pisces: Atherinidae) by brightfield and scanning electron microscopy

Hysterothylacium geschei n. sp. (Nematoda, Anisakidae) is described from the intestine of Cauque mauleanum (Steindachner) (Pisces: Atherinidae) from Lake Panguipulli (39 degrees-43'S; 72 degrees-13'W), Chile. Eleven (78.6%) out of 14 fish were infected, with a mean intensity (range) of 14.4 (1-55) worms. The new species can be differentiated from the two previously described species of freshwater fishes from South America by the presence of lateral alae, the number of caudal papillae, and the length of the spicules, oesophagus, intestinal caecum, distance vulva-anterior extremity and the length ratio intestinal caecum: ventricular appendix. From the fishes examined in Lake Panguipulli, including the introduced salmonid species Oncorhynchus mykiss (Walbaum) and the authochthonous species Basilichthys australis Eigenmann (Atherinidae) and Percichthys trucha (Valenciennes) (Percichthyidae), only one specimen of P. trucha was found parasitized by a third-stage larva of this species.