Family Philometridae

Revised 10/23/22

Philometridae Baylis & Daubney, 1926
Marine and freshwater nematodes, parasites of fish. Often parasitizing the gonads of the host fish. 

Rasheed (1963) indicates that given the absnce of males, the following morphological and anatomical charaters are important for the fsamily Philometridae:

1. The shape and size of the body.

2. The cuticle.

3. The head and cephalic papillae.

4. The esophagus.

5. The tail

Since the anus and vulva are atrophied in the Philometridae, their positions cannot be considered.


Body size: Eggs develop in the uterus and are retained in the body. Consequently, body size is affecetd by the number of eggs produced.

Cuticle: considered important in this family: smooth, thin, with scattered inflations or "bosses", or "rods and cones" projecting from the cuticle.  These characters differ with age of the female.

Head and cephalic papillae: number, shape and size vary with species

Female mouth a simple circular to oval or roughly triangular shape, which is sometimes armed with numerous minute circumoral sclerotized formations (denticles) that support the peribuccal rim internally.

Esophagus: generally cylindrical and somilar among species. In Philometra it is generally swollen anteriorly.

Tail shape: varies among genera


Life Cycle:

All philometrids are ovoviviparous and after fertilization, females become very large as first stage larvae fill their uteri. In fully gravid females the vulva and anus atrophy iexcept in Alinema. The first stage juveniles are dispersed nwhen the female body bursts in contact with water.

Philometrids exhibit a marked  sexual dimorphism in which females are highly modiied  and considerably larger than the males. While males are usually 2-4 mm long, the conspeciic gravid  females may be several centimetres long and even and a length of  more than 1 meter has been reported for one unidentiied species of Philometra

Many genera are blood-feeding and so the body color of females is often pink to red or brown.

The  deinitive  hosts  of  philometrid  nematodes  are  freshwater,  brackish-water  and  marine  fishes.  Many  species feed in various fish tissues while others are n body cavities. Depending on the  species,  philometrids  may  infect,  for  example,  the  skin and subcutaneous tissues, body musculature, eyes, orbits, swimbladder, gonads, circulatory system or body cavity of their fish host (Moravec and de Buron, 2013).

Intermediate hosts of philometrids are copepods, which become infected after ingesting the free-living first stage juveniles released into the water by gravid females. Two molts occur in the intermediate hostís haemocoel and the third stage is infective to the definitive fish host.  Some  philometrids  use fish  paratenic  hosts  as the main  source  of infection (Moravec and de Buron, 2013).

Damage to Host:

Of the many species of philometrids that parasitize marine fishes, the most  pathogenic are  probably the Philometra species that parasitize host gonads (mostly ovaries).

In those tissues they cause inflammation, haemorrhage, oedemas and granuloma formations in both male and female fishes (Moravec and de Buron (2014).



Moravec, F. and Justine, J-L. 2008. Some philometrid nematodes (Philometridae), including four new species of Philometra, from marine fishes off New Caledonia. Acta Parasitologica 53:369-381.

Moravec, F., de Buron, I.  2013. A synthesis of our current knowledge of philometrid nematodes, a  group  of increasingly important  ish  parasites. Folia Parasitologica 60:81-101.

.Rasheed, S. 1963. A revision of the genus Philometra Costa, 1845. J. Helminthol. 37:89-130..

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