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, František 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…
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