17701
Based on available information on copper toxicity and population models , the authors estimated population threshold concentrations at which the population size is stable ( that is , 0 net population growth ) for 13 freshwater species ( 3 algal , 6 invertebrate , and 4 fish species ) .
 Chemical: copper
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities: copper 
Answer:
 Chemical: copper