Philometra floridensis (Nematoda: Philometridae) damages ovarian tissue without reducing host (Sciaenops ocellatus) fecundity

Abstract

The parasitic nematode Philometra floridensis infects the ovary of its only host, the economically important fish species Sciaenops ocellatus, but the factors influencing host susceptibility and potential pathogenic effects are unknown. Here we report new information on these topics from evaluations of infected and uninfected hosts collected from the northeastern Gulf of Mexico. Fish length and age were evaluated vis-à-vis nematode prevalence to check for ontogenetic differences in host susceptibility. To evaluate health and reproductive consequences of infection, we looked for effects in Fulton's condition factor (K ) and batch fecundity estimates (BF), and we evaluated ovarian tissue histologically to check for oocyte atresia and other host responses. We observed localized pathological changes in fish ovarian tissue associated with female nematodes, including leucocytic exudates, granulomatous inflammation, and Langhans-type multinucleated giant cells; the hosts, however, appeared to maintain high fecundity and actually exhibited, on average, better health index scores and higher relative fecundity than did uninfected fish. These differences are likely explained by the parasite's tendency to disproportionately infect the largest, actively spawning fish and by the localization of pathogenic changes, which could have masked effects that otherwise would have been reflected in mass-based health indicators. Although we did not detect negative effects on measures of overall health or reproductive output, further research is needed to better elucidate the relationship between these parasites and other factors affecting host reproductive potential, such as egg quality.

Occurrence and prevalence of Philometra filiformis (Stossich, 1896) on Pagellus erythrinus (Linnaeus, 1758) in the Southern Tyrrhenian Sea

“…In fact, a higher prevalence of Philometra sp. in the ovary than in the testes was found in Paralichthys adspersus , Glaucosoma ebraicum , Cynoscion nebulosus , Genypterus chilensis and Sciaenops ocellatus (Oliva et al., ; Hesp et al., ; Perez et al., ; Chávez and Oliva, ; Bakenhaster et al., ). Philometrids often affect only one gender of a given species (Moravec and de Buron, ); similarly in this case, no male gonads of P. erythrinus were parasitized.…”

Histopathological changes on the gills of asp (Aspius aspius) and European catfish (Silurus glanis) caused by Lamproglena pulchella and a Lamproglena sp. (Copepoda: Lernaeidae), respectively

“…In mammals and birds, degeneration processes are often followed by formation of giant cells, and in fish, their presence is only rarely mentioned mostly with nematode infections. In these rare instances, Molnár, Szakolczai, and Vetési () observed them in the swim bladder with Anguillicola crassus Kuwahara, Niimi & Itagaki, 1974 infection due to invasion of second stage larvae, while Bakenhaster, Lowerre‐Barbieri, Kiryu, Walters, and Fajer‐Avila () found giant cell formations with Philometra infections of fish. No information is available about giant cell formation at infection of fish in parasitic copepods.…”

Occurrence and consequence of the parasitic nematode Philometra piscaria (Moravec & Justine, 2014) on Epinephelus coioides (Hamilton, 1822) from the southeast coast of India

“…Studies of the effects of Philometra on fish ovaries are uncommon, as are those addressing parasitism of fish gonads in general [16]. Bakenhaster et al [18] reported that nematode (Philometra floridensis) parasite infection resulted in reduced fecundity in Sciaenops ocellatus as a result of the effective volume of the ovaries was reduced. Infected ovaries of Channa punctata exhibited necrosis and decrease in the yolk formation due to the disappearance of vitellogenic oocytes.…”

“…The present observation attributes towards that nematode P. piscaria larvae resulted in a decrease in the formation of atretic follicles during reproductive period potential of infected host fish. Bakenhaster et al [18] reported the histopathological changes caused by the Philometra floridensis in Sciaenops ocellatus which revealed damaged oocytes showing signs of necrosis, damaged and disrupted germinal epithelium, liquefaction of yolk globules and reduction in yolk formation in infected ovaries.…”