The general life cycle of all three grub species includes a bird host (e.g., herons, kingfishers, and cormorants), and a snail intermediate host (Physa spp., white grub and Helisoma (= Planorbella) spp., black and yellow grub) (Figure 1). The parasites mature and sexually reproduce in the bird, releasing eggs that are voided in the bird’s feces. In water, eggs embryonate and release a free-swimming miracidium that seeks out and penetrates the snail host. Once inside an appropriate snail host, the grub asexually reproduces, ultimately releasing swimming cercariae. Cercariae seek out and penetrate host fishes, developing into the characteristic “grubs” in the fish flesh.

In larger fish these trematodes give the fish a “wormy” appearance, rendering it unmarketable, as most consumers do not find the wormy appearance aesthetically pleasing. It is important to note that the asexual multiplication of the worm inside the host snail greatly increases the risk of infection to the next host (i.e., the fish), and exacerbates the problem of control. For example, a given infected snail may release tens to hundreds of cercariae each day over a several month lifespan. This amounts to thousands (to millions) of potential grubs in infected fish resulting from very few infected snails.

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Aquatic Grub Control