Cause of increased size of acipenseriform eggs infected with Polypodium hydriforme

Eggs of acipenseriform fish infected with the parasite Polypodium hydriforme become enlarged during later stages of development. This study examined if the increase in size is due to the increase in nutrients or water in the infected eggs and if the polypodium eggs affect the nutrient levels of the neighbouring eggs in the ovary. Infected and uninfected eggs were collected from parasitized Paddlefish, Polyodon spathula, hosts and unparasitized individuals. Levels of water, protein, carbohydrates, lipids and amino acids were determined for each egg. Although there were nutritional differences between eggs infected with P. hydriforme and uninfected eggs there was no indication that there was an increase in resource allocation to the infected eggs. The amount of water was much higher in infected eggs, suggesting the size increase was due to a greater influx of water. Levels of free amino acids were much higher in infected eggs and we hypothesize they could be used to increase the solute concentration to increase the influx of water, a mechanism that is also used by marine teleosts.