Tolerance of Juvenile Paddlefish to Salt for Control of Ichthyophthirius multifilis

Salt can be used to control parasites when the salinity tolerance limits of the culture fish exceed those of the parasite. Ichthyophthirius multifilis, known as ICH, is a parasite that is known to infect paddlefish and can cause total mortality. ICH can be controlled with salt between 3 and 6 g/L. However, salinity tolerance of juvenile paddlefish is not well defined. The objective of this project was to evaluate the salinity tolerance of juvenile paddlefish at salinity levels ranging from 3 to 10 g salt per L over a 96-hour period. In Study 1 with salinities ranging from 3 to 7 g/L, there were no fish mortalities. Even though swimming behavior appeared normal, the fish lost 19% of its body weight in water containing 7 g salt/L. In Study 2 with salinities ranging from 6 to10 g/L, fish also had increasing weight loss with increasing salinity. In water containing 9 and 10 g/L, fish lost balance in 24 hours and swam in a spiral motion. In addition, these fish became bloated and discolored. Fish mortality started at 8 g/L and increased with the salinity. Water quality parameters were within acceptable range for juvenile paddlefish in both studies. When the salt level was less than 7 g/L, juvenile paddlefish did not show body weight loss or other physical sign of stress over a 96-hour period. Therefore, salt levels between 3 and 6 g/L for 4 days should be adequate to eliminate the ICH parasite without adversely affecting the health of the fish