A large portion of the fish emulsion used in fertilizers comes from the little fish called menhaden caught in the Atlantic and the Caribbean oceans. It is not caught as a human food source since it is such a fishy, bony and oily fish. Instead it is used primarily for fish meal and fish oil, both of which are in high demand. The menhaden swim in huge schools, and are caught in huge nets by the fishermen.
The boats come ashore and unload their fish onto long conveyor belts that pass into a heated oven where they are baked at about 200 degrees (F). This keeps the fish from spoiling and it firms up the tissue so it can be used in the fish meal. In non-organic fertilizers, scraps of fish are used, instead of the whole fish and more additives are used later.
Baked menhaden are fed into large screw presses which force the oils and liquids out of the meat of the fish. The meat solids are collected and further processed to be sold as the fish meal used in pet foods and the liquids are fed on to be further refined.
Fish oil is a very valuable commodity, especially in the health food market, so it is removed from the pressed fluids through the use of a centrifuge which spins the oil out of the mix. The remaining fluid now moves on to be reduced.
The oil-free fish fluid still contains a lot of nutrients and so it is poured into large vats where it can be boiled down into a thick fluid sold as fish emulsion. Often phosphoric acid is added at this point to keep the enzymes from spoiling the emulsion. The amount added is low enough that they can still call it organic fish fertilizer.
Finally, the thickened fish emulsion is bottled and shipped off to stores to be sold as organic fish fertilizer.