Fish most definitely! Jokes aside, you should definitely invest in some quality equipment. Some essential equipment includes things such as a filter and light. Then, depending on the types of fish you have, you may want to consider purchasing things like aquarium heater. In order to help mimic your fish’s natural habitat, you’ll also want to purchase decorations. rocks, aquarium caves, plants - life and fake, and statues are great options to make a tank feel a bit more like home.