The copepod (Acartia tonsa) is a species widely cultivated in research laboratories and it has proven valuable as feed for fish larvae in mariculture. The overall ecology of A. tonsa has been studied for decades, but reports on genetic responses to environmental stress in A. tonsa have only recently started to appear. For other copepod species, on the other hand, arow of studies have shown that stress related genes, such as Hsp70 and Hsp90, are expressed at elevated levels as response to, e.g., temperature stress and exposure to chemicals.