Pleistophora infestation in fathead minnows, Pimephales promelas (Rafinesque)

Area of Science:

• Ichthyology
• Parasitology
• Aquatic Animal Health

Background:

• Pleistophora species are known microsporidian parasites affecting fish.
• Ovarian infections can impact fish reproduction and health.
• Fathead minnows (Pimephales promelas) are common model organisms in aquatic research.

Purpose of the Study:

• To identify and characterize a Pleistophora infestation in adult fathead minnows.
• To investigate the pathological effects of the parasite on fish ovaries.
• To differentiate between potential Pleistophora species based on observed parasitic stages and host condition.

Main Methods:

• Histopathological examination of infected ovaries.
• Ultrastructural identification of parasitic stages.
• Comparison of morphometric and physiological parameters between infected and non-infected fish.

Main Results:

• Parasitic stages of a microsporidian, identified as likely Pleistophora ovariae, were found exclusively in the ovaries of adult fathead minnows.
• Infection led to oocyte degeneration and ovarian inflammation.
• No significant differences were observed in body length, weight, gonadal weight, gonadosomatic index, or plasma vitellogenin levels between parasitized and non-parasitized females.
• Male fish testes were unaffected.

Conclusions:

• Pleistophora ovariae is the probable causative agent of ovarian microsporidiosis in the studied fathead minnows.
• The parasite causes localized ovarian pathology but does not appear to systemically affect host health metrics under these laboratory conditions.
• Further research is needed to understand the transmission and broader ecological implications of this ovarian parasite in fish populations.