Like any good ichthyologist, I keep saltwater fish. When I lost a Banggai cardinalfish recently, how did I deal with this tragedy? Not by flushing it or starting a pet cemetery, but by turning that loss into a gain for the Biodiversity Institute's Ichthyology collection.
It is true that aquarium fish make less than ideal specimens. It is impossible to get accurate, reliable information on the natural habitat, behavior, distribution, and population structure of such a specimen. However, for large-scale genetic studies, a specimen without such data can still provide valuable insight into the evolutionary relationships among fish species. Likewise, we can gain important morphological information to further inform our ideas on the evolution of structures like jaws and tails.
So how does a fish reach scientific immortality after passing on to the great aquarium in the sky? First, and not surprisingly, it's important to get the fish into the freezer as soon as possible to keep it from decomposing (genetic material starts to break down quickly as the fish decomposes). When we are ready to process the fish, we first take photos of it, since preservation often causes bright colors and patterns to fade. Then a small piece of muscle is taken from one side and added to our tissue collection--this leaves the other side of the fish intact for morphological studies. We then inject the fish with formalin and store it in alcohol, or clear and stain it.
While at first blush this may seem perverse, my cardinalfish now lives on as frozen tissue and fluid specimens, where it will provide valuable genetic and morphological information for researchers and students. I know I would much prefer that to being flushed.