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US Fish & Wildlife Service FieldNotes

LIVINGSTON STONE NFH: Investigation into New Rearing Conditions for Delta Smelt, Are Snails Really Needed?

Region 8, August 14, 2012
Rams-horn snails Helisoma anceps
Rams-horn snails Helisoma anceps - Photo Credit: n/a

By Jeremy Shannon, USFWS

The UC Davis Fish Conservation and Culture Laboratory (FCCL) outside Byron, California, has traditionally relied upon small freshwater rams-horn snails as an aide to keep algal growth at bay in the tanks used for rearing endangered Delta Smelt. These snails, Helisoma anceps, are common air-breathing freshwater gastropods found in waters across North America.

Under recirculating aquaculture conditions, the snails are added to the tanks to graze upon algae and excess feed and help to keep the tanks, plumbing, etc., a bit freer of algae buildup that could ensnarl and immobilize fish larvae. Recently, there have been concerns regarding use of these snails for algal control due to the possible transfer of disease and parasites from snails to fish and this has led to an investigation into raising fish without the use of the snails.

Delta Smelt eggs were spawned and incubated in the traditional fashion, but hatched larvae were transferred into tanks lacking snails beginning in April 2012. Tanks were closely monitored for algae growth and food buildup. Feedings were adjusted based on these observations, and fish were moved to clean tanks of the same size at 20 days old. At 40 days old, fish were counted and moved into larger juvenile tanks with no snails. Again, these tanks were closely monitored for algae growth and food buildup, and feedings were adjusted based on these observations. Fish were moved to a clean juvenile tank at 60 days old and observations continue.

So far, smelt survival among the populations in these “no snail” tanks has been in the typical range found in the past; fish size is comparable to those reared with the snails. Initial observations seem promising, but the experiment is ongoing. These trial populations are adding to the ever evolving knowledge of Delta Smelt aquaculture techniques, which in turn helps us to greater understand this species and its needs.

Contact Info: John Rueth, 530-275-0549, john_rueth@fws.gov