Abstract
Parasite communities of Chionodraco hamatus were investigated from Terra Nova Bay (Ross Sea, Antarctica) during host spawning time. Special attention was given to helminth infracommunities and effect of host sex on its structure. A total of 21 taxa including 5 ecto-parasites and 16 endo-parasites were identified. The number of ecto and endo-parasite species per individual host ranged from 1 to 3 and 3 to 10, respectively, while the mean numbers of parasite specimens per individual host were 4.7 and 1309.7, respectively. The rich abundance of infection suggests a rich concentration of helminth intermediate/paratenic hosts in the coastal waters of Terra Nova Bay. Chionodraco hamatus serves as a definitive host for 10 helminth taxa, while it acts as an intermediate/paratenic host for 6 helminth taxa. Larvae of 6 helminth taxa for which C. hamatus serves as intermediate/paratenic host represented 98.7% of all specimens found. Of these, the tetraphyllidean and diphyllobothridean cestodes and the nematode Contracaecum osculatum s.l. were the most prevalent and abundant. ‘Larval’ infracommunities had significantly higher species richness, total abundance and diversity than ‘adult’ infracommunities, suggesting the important role of C. hamatus in supporting the life cycles of those parasites in the study area as a paratenic/intermediate host. Significant differences in the pattern of helminth infracommunities of larval forms between male and female fish were found. These differences could be caused by physiological, and most probably by behavioral differences between sexes suggesting that sex is an important factor influencing parasite burden in C. hamatus during reproductive season.
Highlights
Icefish belonging to Channichthyidae, a family unique among vertebrates in that they lack haemoglobin, live in the cold-stable environment of the Southern Ocean and include between 15 to 17 recognized species [1,2]
We studied a total of 100 C. hamatus sampled in January 2012 (n = 50), and February 2013 (n = 50) by hand line or net at benthic depths ranging from 110 to 160 m in front of the Mario Zucchelli Station in Terra Nova Bay (74u 419S – 164u 059E/74u 419S – 164u 049E)
Data analysis Apart from analyses based on all parasite taxa, we focused on endo-parasites and on the basis of parasite stage we considered two helminth categories in the description analysis, and interpretation of infracommunity structure, i.e. the ‘larval’ infracommunity and the ‘adult’ infracommunity [19]
Summary
Icefish belonging to Channichthyidae, a family unique among vertebrates in that they lack haemoglobin, live in the cold-stable environment of the Southern Ocean and include between 15 to 17 recognized species [1,2]. Among the nine species occurring in the Ross Sea (Eastern Antarctica), C. hamatus is the most abundant [3]. It has a high-Antarctic type of distribution being limited to shelves close to the Antarctic continent, where it feeds mainly on euphausiid crustaceans and benthic and mesopelagic fishes according to local and seasonal availability [1,2,3]. Despite its common occurrence in the Ross Sea, quantitative helminthological studies of C. hamatus have been focused so far on specific parasite taxa and limited to occasional examination of incomplete individual hosts [4,5]. Most studies were on taxonomic features of specific taxa, description of new or re-description of poorly known species [5,6], larval anisakids identification by genetic markers [7], or pathological changes by larval helminths [8].
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