Seriously Fish is an online reference for freshwater fish enthusiasts, offering detailed information on 1,822 species. Established in 2009, the site helps aquarists research fish by name, classification, type, or geographic origin. Its species profiles include practical aquarium guidance such as water parameters and tank size, alongside photographs and cited sources where available. Visitors can explore 103 families and 552 genera, browse fish from regions and countries around the world, and use a glossary explaining 1,702 terms.

The site also supports people new to fishkeeping with guidance on choosing suitable fish, assessing a tank, and understanding topics such as pH and water hardness. Its articles cover research, conservation, and fieldwork. Seriously Fish invites contributions of measurements, photographs, and publications, with submissions reviewed by its community. It also connects fishkeepers through the Aquatica Discord. The reference is continually developing: the site identifies missing information in some profiles and notes plans to expand its coverage to aquatic plants and invertebrates, including shrimp, snails, and crayfish.