I'm thinking the same thing, Will...the article is about saltwater creatures, and when it mentions freshwater it states freshwater shrimp don't absorb minerals from the environment, but rather intake through diet.
"Fish and shrimp live in a hypertonic environment and drinking salt water may partly fulfill of their mineral requirements (NRC, 1983). Also they make with the direct absorption of minerals through the gills, fins and skin. The situation in freshwater fish and prawns is the reverse .Freshwater fish and prawns are therefore more demanding on an adequate dietary mineral supply than marine fish and shrimp (Cowey and Sargent, 1979)."