Over the past few decades there has been increasing concern about acidification and metal contamination in lakes, rivers, streams, and oceans. Although problems such as acidification and metal contamination may not have serious short term effects on the survival of teleost embryos, they may have long term effects on reproductive success. Problems and adaptations associated with ion and osmoregulation in adult freshwater teleosts.
Freshwater fish are hyperosmotic relative to the external water.
As a result they are faced with the problems of gaining water through their gills and losing salts through their gills and kidneys. Freshwater fish have evolved mechanisms to combat these problems. To maintain water balance they can excrete copious amounts of dilute urine. They are able to maintain their solute content by eating food and actively uptaking salts through their gills Fig. Overview of the stucture of a typical salmonid egg.