Formalin is very irritating to your eyes and skin. Work only in a well ventilated space when using it, and never sniff it to detect its presence. You should be sure to label your fishes as to locality and date collected. Habitat information and method of capture recorded either on a label or in a permanent system of file cards or a notebook. Giving each labeled jar a number will make reference to the information much easier.
Many collectors keep files or a notebook of every collection they make.
These sources contain the habitat information and species lists of all specimens caught in each collection. The first three letters are the initial of the collector. Your labels should be written on good quality paper in waterproof ink, and placed inside the jar with your specimen. After the period in formalin, the specimens should be allowed to soak in pure water for a few days to remove most of the irritant. They can then be handled safely for identification.