Pseudochaenichthys georgianus, Norman, 1937

Kuzmina, T. A., Salganskiy, O. O., Vishnyakova, K. O., Ivanchikova, J., Lisitsyna, O. I., Korol, E. M. & Kuzmin, Yu. I., 2022, Helminth Diversity In Teleost Fishes From The South Orkney Islands Region, West Antarctica, Zoodiversity 56 (2), pp. 135-152 : 142

Pseudochaenichthys georgianus

In the South Georgia icefish, 16 helminth species were recorded (from 3 to 12 species per host), including 3 species of trematodes, 4 species of cestodes, 5 species of nematodes and 4 species of acanthocephalans (table 3). Estimated species richness was 18 (Chao1), 19 (jackknife) or 17 (bootstrap) species. The diversity indices equalled 1.54 (Shannon), 0.68 (Simpson), and 0.55 (Pielou’s evenness).

All the cestode species, as well as the nematodes Anisakis sp. , Contracaecum sp. and Pseudoterranova sp. and acanthocephalans Corynosoma spp. parasitize P. georgianus on larval stages. Thus, P. georgianus is considered to be a definitive host for 6 out of 16 helminth species recorded. As in the mackerel icefish, cestodes predominated in the helminth community of P. georgianus ; together they comprised 78.7 % of the total helminth number ( fig. 1 ).

According to the prevalence of infection, 8 species predominated in the helminth community in P. georgianus (table 3). Bilocular and trilocular metacestodes had an infection prevalence higher than 95 %. The cestode Diphyllobothrium sp. , the trematodes M. pennelli and N. georgiensis , the nematodes Contracaecum sp. and Pseudoterranova sp. had an infection prevalence of 70–95 %. The nematode D. fraseri and monolocular metacestodes were common, with the infection prevalence of 36.4 % and 45.5 %, correspondingly. Other 8 species of helminth occurred in less than 30 % of examined P. georgianus .

In all three latter fish species, the proportion of helminth species found on larval stages was larger (62.5–75 %) than that of the species represented by adult parasites (25–37.5 %) ( fig. 2 ).

The helminth species richness appeared to be much higher in fishes from shallowwater (10–30 m deep) habitats than in deep-water (60–800 m) habitats (table 4).

Analysis of similarity between helminth faunas in studied samples of shallow- and deepwater fishes (table 5) revealed the highest similarity of helminth faunas in two shallow-water species from the Ukrainian Antarctic Station area: P. charcoti and N. coriiceps (SØrensen index 90.6 %) and C. aceratus with N. coriiceps and P. charcoti (88.0 % and 89.8 %, respectively). Also, helminth faunas of deep-water populations of C. aceratus and P. georgianus were similar (SØrensen index 88.9 %). The lowest similarity was recorded for the helminth fauna of the deep-water population of C. gunnari ; the similarity between N. coriiceps and C. gunnari was minimal (20.0 %).

Visualization of the helminth faunal similarities according to the Bray-Curtis index using the cluster analysis ( fig. 3 ) showed a clear division of groups of shallow- and deepwater fish species.

According to the results of the SIMPER analysis, the overall dissimilarity between the helminth communities of shallow- and deep-water fishes was 80.1 %. Four helminth species had the largest contribution to the dissimilarity: the acanthocephalan Corynosoma pseudohamanni (19.4 % contribution), anisakid nematodes Contracaecum sp. (17.4 % contribution) and Pseudoterranova sp. (14.4 % contribution), and trilocular metacestodes (11.4 % contribution). Infection of shallow-water fishes with C. pseudohamanni and anisakid nematodes was more than 10–15 times higher, while deep-water fishes had 168 times higher infection with trilocular metacestodes.

Figures

Fig 3. Cluster analysis of the similarity between the helminth communities of the shallow-water (SW) and deepwater (DW) populations of fish species determined by the Bray-Curtis index.

Fig. 1. Proportion (%) of four parasite taxa in three fish species from the South Orkney Islands area, West Antarctica.

Fig. 2. Proportion (%) of helminth species parasitizing three teleost fishes from the South Orkney Islands area, West Antarctica on larval and adult stages.