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OLAW has made the determination that all stages of zebrafish (Brachydanio or Danio species) development greater than three days postfertilization (dpf) must be described in animal-use protocols. Zebrafish from four days postfertilization onward are considered animals, and therefore must be counted.
This policy acknowledges that making exact counts of zebrafish larval forms and adults is difficult, and allows knowledgeable investigators to rely on experience and expertise to arrive at estimated counts that accurately reflect numbers of zebrafish four dpf and older that are used.