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The two stressors were the myxozoan parasite , Tetracapsuloides bryosalmonae , which is the etiological agent of proliferative kidney disease ( PKD ) and a natural stressor to salmonid populations , and 17 beta - estradiol ( E2 ) as prototype of estrogen - active chemical stressors in the aquatic environment .
 Chemical: 17 beta - estradiol; Chemical: estrogen
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: 17 beta - estradiol; Chemical: estrogen