Fish handle salt water by actively transporting the chloride ions (one of the major ions in seawater – which is mostly sodium chloride) out of their cells. Euryhaline fish (those fish that can go back and forth between salt and fresh) usually do so as part of their lifecycles – e.g. salmon lay eggs in freshwater, but migrate and mature as adults in the ocean. There are fancy words for this – anadramous fish like salmon breed in freshwater and move to saltwater, while catadromous fish (such as the American eel) spawn in seawater and return to live in freshwater as adults. To survive in saltwater, these fish ‘turn on’ a set of genes coding for proteins that actively transport the salt from their tissues, and also alter their gills. Notable among these genes is CFTR, the cystic fibrosis transmembrane conductance regulator – the same gene that is partially or completely dysfunction in cystic fibrosis! In fact, studies of CFTR in euryhaline fish have contributed to our knowledge of this inherited human disease!
Fish handle salt water by actively transporting the chloride ions (one of the major ions in seawater – which is mostly sodium chloride) out of their cells. Euryhaline fish (those fish that can go back and forth between salt and fresh) usually do so as part of their lifecycles – e.g. salmon lay eggs in freshwater, but migrate and mature as adults in the ocean. There are fancy words for this – anadramous fish like salmon breed in freshwater and move to saltwater, while catadromous fish (such as the American eel) spawn in seawater and return to live in freshwater as adults. To survive in saltwater, these fish ‘turn on’ a set of genes coding for proteins that actively transport the salt from their tissues, and also alter their gills. Notable among these genes is CFTR, the cystic fibrosis transmembrane conductance regulator – the same gene that is partially or completely dysfunction in cystic fibrosis! In fact, studies of CFTR in euryhaline fish have contributed to our knowledge of this inherited human disease!