Yes, any aerated or non-aerated fish/aquarium water is a great fertilizer. (mostly nitrogen and phoshorus), but that is NOT the same as fish emulsion or fish meal.
Fish meal and fish emulsions are made from cooked, slightly composted, fish scraps (mostly the leftover parts of the menhaden fish). The menhaden fish is an oily fish, kin to the herring and sardine. The best parts of the fish is sold off as cat food products and cosmetic products. The leftover stuff is made into natural fertilizing products.
Because of the process, most commercial fish emulsions contain absolutely no fish oils and mainly no beneficial aerobic microbes in the bottles. Think about it! If fish emulsions had aerobic microbes growing in them, the bottles would explode on the shelves! (LOL)
Fish meals, on the other hand, may have a touch of fish oils in them, but they contain more cooked, ground up fish flesh and bones, based on the factory's recipe for the product.
Any whole fish scraps that you can put in your compost pile, garden beds, or in special aerobic compost tea recipes, will have far more nutrients and a wider variety of beneficial microbes in it, than most commercial fish meals or emulsions anyway.
The entire Kingdom of God can be totally explained as an Organic Garden (Mark 4:26)