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Using a microarray approach contrasting parasite - infected and non - infected rainbow trout at low or high estrogen levels , it was observed that molecular response patterns under joint exposure differed from those to the single stressors .
 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: estrogen