resulting in skin rashes. Any direct skin contact with formalin should be avoided by wearing rubber gloves. If formalin does accidentally contact skin or eyes, the affected area should be washed immediately with water.
For fixing fish tissues, a 10-percent buffered formalin solution (one
part formalin and nine parts water) is recommended. Three grams of borax
are added per liter of fixative to act as a buffer, neutralizing the pH of
the formalin, retarding tissue shrinkage, and preventing decalcification
of the tissues. Buffered formalin is poured into a plastic collection
jar, and a collection label (fig. 6) is placed inside the jar with an
additional label taped to the outside of the jar. Labels should be
preprinted on waterproof paper using ink that is resistant to water,
formalin, and alcohol, and the information should be recorded on the label
using a lead pencil.
Figure 6.--Suggested collection label.
All fish to be preserved are first killed by overdose of carbon dioxide. When placing the fish in the collection jar, care should be taken to ensure that buffered formalin is not splashed into the investigator's mouth or eyes. For fish more than 150 mm in length, an incision about 30 mm long is made along the abdominal body wall on the right side of the fish to ensure penetration of fixative into the body cavity. Fish should be left in buffered formalin for 2 days to 1 week to ensure fixation of tissues.
Permanent preservation of fish specimens requires removing them from buffered formalin after fixation of tissues has occurred. The buffered formalin is treated as a hazardous material and is properly discarded according to State and local guidelines, and the fish is soaked in tap water for 48 hours with one change of tap water during this period. After 48 hours, all tap water is discarded and 40-percent isopropyl alcohol or 70-percent ethanol is added to the collection container for permanent preservation.