Methods for preserving fish:

A) For collection specimens:

Fish should be fixed in 5-10% formalin for several days to a week. Larger specimens being left in the solution for a longer time. Larval fish need only 1 day to fix the tissue. After fixing rinse in fresh water several time and place specimens in 75% ethyl- or isoproply alcohol.

Never transport formaldehyde solutions on airplanes. If formaldehyde can not be purchased where you going take paraformaldehyde and prepare the solution as detailed below.

B) For studies involving DNA:

Tissue for molecular studies can be fixed in 95-100% ethyl alcohol. A weaker solution is OK to start if you can not get 95-100% ETOH. You can generally get 70-95% ETOH in Latin America in pharmacies. However, check before you go since it is impossible or very expensive in a few countries like Belize.

4% Paraformaldehyde = 10% Formalin


Used to fix and preserve fish. Large specimens should have the body cavity cut to allow the solution to enter and fix the internal organs. Very large specimens also need to be injected with the solution to prevent internal tissues from rotting. For small specimens a 5% solution can be used.

Directions: (for 1000 ml)

1. Make 500 ml of 8% paraformaldehyde: Combine 45 g paraformaldehyde with about 400 ml of water in an Erlenmeyer flask. Place on low heat (do not exceed 60 0C) and stir for about 15 minutes in the fume hood. Then add 5 or 10 drops of 1N NaOH (sodium hydroxide) solution. When the solution is clear, remove from heat, and add water as necessary to bring to 500 ml.

2. Dilute 2X with water to make a 4% solution (= to 10% formalin)

Caution: Paraformaldehyde fumes are dangerous


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