Two snail types which pose threat to hybrid striped bass culture.While working around the ponds at BCC, I'd seen one pond where quite a number of the ram's horns snails lay along the embankment. I went back to collect some for display and identification. (I collect mollusk shells). While there, instructor John Baka informs me of a second disease aside of yellow grub (caused by Ram's Horn), it is the white grub. I collected some of the Ram's Horns snails, however unfortunately I did not obtain any live samples. Planorbis was plentiful, which I do have live samples.
John picked up a small piece of driftwood in the pond and showing the underside explained they were all snail eggs! I took the sample home with me, and took a look under the microscope.
Full resolution image of snail eggs on driftwood(Planorbis sp.) commonly called a ram's horn snail is involved in the life cycle of
Yellow Grub and
Physella sp. is involved in the life cycle of
White Grub.
Full resolution image of snail eggs.Yellow grub in Hybrid Striped Bass Culture.
(
Clinostomum complanatum), a digenetic trematode is the most economically devastating disease & parasite problem encountered. These parasites are characterized by their life cycle... having a definitive host (birds) a first intermediate host (snails) and a second intermediate host (fish).
Full resolution image of snail eggs
Magnification 40xDevelopment of Methods for Controlling Parasitic Grub Infection Utilizing Intensified Tank Production and Fingerling Pond Modification in Hybrid Striped Bass Aquaculture
Summary: In 1997, an outbreak of an unidentified white grub disease caused high losses of fry and Phase-I fingerlings in a hybrid striped bass hatchery. With collaboration from North Carolina fish farmers, an examination into the identity, biology, and possible control strategies for this grub was conducted.
Partial experimental completion of the grub’s life cycle, analysis of grub DNA and historic reports of grub disease has indicated that the suspect grub is the common white grub Posthodiplostomum minimum.
Infection with this severe grub disease is attributed to exposure of very young fry with immature immune systems to massive numbers of cercariae — the piscine infective stage of the parasite — in the fry ponds.
The life cycle of P. minimum includes the great blue heron as definitive host, the snail host Physella sp. and a variety of fish hosts. The massive number of cercariae within the fry ponds can be attributed to large, uncontrolled populations of Physella sp.
if the snail population can be eliminated prior to fry production, the disease can be avoided.
It is recommended that fry ponds be used only for the production of Phase-I fingerlings. Further, when not being used for the production of Phase-I fingerlings, the ponds and any remnant pools should be kept drained, thoroughly dried, and tilled or plowed regularly. This would effectively eliminate any active or dormant snail populations and provide the hatchery with 2.5 to 3 months of grub-free fingerling production before snail and parasite populations reach a level that would be pathogenic to the young fish.
Source:
NC Sea GrantComplete
Research Report in PDF Format.
Side-note.
How this snail got its spots...
Read More »
