Friday, 10 April 2015

Philometrid Nematodes from Perciform Fish off the north Australian coast.

Philometrids are large Nematodes parasitizing Fish . They show a high degree of sexual dimorphism, with males typically only a few mm in length, while females may reach tens of centimetres. The females give birth to live young.

In a paper published in the journal Parasite on 6 February 2015, FrantiĊĦek Moravec of the Institute of Parasitology of the Biology Centre of the Academy of Sciences of the Czech Republic and Diane Barton of Fisheries Research at the Department of Primary Industries & Fisheries of the Northern Territory and Aquatic Ecology & Management at the Research Institute for the Environment and Livelihoods at Charles Darwin University, describe two species of Philometrid Nematodes from Perciform Fish off the north Australian coast.

The first species is placed in the genus Philometra, and given the specific name protonibeae, in reference to its host species, the Blackspotted Croaker, Protonibea diacanthus. The males of this species reach 3.37–3.90 mm in length; no gravid (i.e. fully mature and pregnant) female was recovered intact, but the largest partial specimen was 427 mm (42.7 cm) in length. The nematodes were found within the ovaries of female Blackspotted Croakers caught at Camdem Sound in Western Australia and Fenton Patches and Ruby Island in the Northern Territory. About 25% of Fish examined were infected, and since the host species has a broad Indo-West Pacific distribution, it is likely that the parasite has a similar distribution.

Philometra protonibeae, left: (A) Anterior end of gravid female, lateral view. (B) Cephalic end of gravid female, apical view. (C) Caudal end of male, apical view. (D) Anterior end of male, lateral view. (E) Anterior end of gravid female (another specimen), lateral view. (F) Larva from uterus, lateral view. (G) Posterior end of gravid female, lateral view. (H) Anterior end of nongravid female, lateral view. (I, J) Posterior end of male, ventral and lateral views. (K, L) Distal end of gubernaculum, dorsal and lateral views. (M) Distal end of spicule, lateral view. (N) Caudal end of gravid female, lateral view. (O) Posterior end of nongravid female, lateral view. Right: (A, B) cephalic end of subgravid female, subapical and apical views. (C) Caudal end of male with protruded spicules and gubernaculum, lateral view. (D) Protruded distal ends of spicule and gubernaculum, lateral view. (E) Distal end of gubernaculum, dorsal view (arrow indicates elevated triangular structure). (F) Caudal end of male, apical view (arrow indicates phasmid). Abbreviations: a, group of four flat caudal papillae; s, spicule. Moravec & Barton (2015).

The second species is also placed within the genus Philometra, but is not assigned to a species as only the females were discovered, and female members of this genus can be very hard to distinguish. Nevertheless it is thought that this is a new species, as it is the first member of the genus described from the John’s Snapper, Lutjanus johnii, and species of Philometra tend to be host specific. The species was found infecting the ovaries of female Fish caught at Bynoe Harbour, Lee Point and Nicol Island, all in the Northern Territory; 45.5% of inspected Fish were infected. One complete gravid female was recovered, this being yellowish in colour and 47 mm in length, as was a subgravid female, 32 mm in length, and two nongravid females, 11.97 and 2.49 mm in length.

Philometra sp. from Lutjanus johnii. (A) Anterior end of largest gravid female, lateral view. (B, C) Posterior end of smaller gravid female, lateral and dorsoventral views. (D) Larva from uterus, lateral view. Moravec & Barton (2015).

See also…

Capillariid Nematodes are parasitic worms infecting a variety of different Vertebrate hosts. The group is split into 22 genera, of which nine are parasites of Fish. Members of the genus Capillaria cause infections in...

Pinworms, Oxyuridae, are parasitic Nematodes infecting the digestive tracts of Mammals. They have short life cycles, typically undergoing several generations in a year, with eggs being released in the host’s faecal matter to infect new hosts. Some species of Pinworm appear to be quite cosmopolitan, infecting...

Parasitic Nematodes of the superfamily Heterakoidea are typified by having three lips, an esophagus with a valved bulb, thick shelled eggs and a pre-anal sucker on the males. They are typically parasites of the digestive tracts of small vertebrates, which do not require an intermediate host (i.e. the species only needs to infect one species of hosts, rather than...

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