13931
While Cu levels were higher in the Cu - pre - exposed fish than in the control fish at T , net Cu accumulation was faster in the control fish than in the Cu - pre - exposed fish during the subsequent high - level Cu exposure .
 Cu, Cu, Cu, Cu, Cu
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Cu, Cu, Cu, Cu, Cu