Temperature alters reproduction and maternal provisioning in a fish ectoparasite

This study quantified the effects of temperature on reproduction and maternal provisioning of the ectoparasite, Neobenedenia girellae (Platyhelminthes: Monogenea), a species known to cause detrimental impacts to aquaculture fishes in tropical and subtropical environments worldwide. At 20 and 25 °C, parasites exhibited relatively slower production of larger eggs that were energy-dense. In contrast, parasites at 30 °C attained sexual maturity faster, were reproductively active over a shorter period, grew to a smaller size and laid smaller, less energy-rich eggs at a faster rate. As such, parasites exhibited two distinct reproductive patterns in response to temperature: parasites at lower temperatures produced larger eggs with higher energy content, while those at the higher temperature had a higher rate of egg production. Larger eggs produced under cooler conditions were better provisioned with energetic reserves and important, membrane-bound lipids that would likely facilitate larval longevity and development success. This is commensurate with previous observations of epizootics of this parasite species in aquaculture systems during winter. Meanwhile, eggs produced at 30 °C contained higher proportions of saturated fatty acids compared with polyunsaturated fatty acids, likely reflecting metabolic regulation of cell membrane fluidity, which is necessary for larvae to survive warm conditions. This study demonstrates that fish ectoparasites have evolved substantial reproductive and metabolic flexibility to maximise infection success under variable environmental conditions.