CatchRules

Fish identifier

What Fish Is This?

Upload a photo of your catch and this free tool names the species in seconds. It compares your image against 1,494 marine and freshwater species and returns the closest matches with a confidence score, so you can check the runner-up when two species look alike. No sign-up, no account, nothing stored.

Drop a fish photo here

or take one with your camera

1 free identification · No sign-up · 1,494 species · Photos aren't stored

How the fish identifier works

The classifier is a vision model trained on wild North American sport fish and invertebrates rather than on general photography. When you upload an image it scores that image against 1,494 species and returns a ranked shortlist, each entry with a confidence figure and a link to that species' profile.

It returns a shortlist rather than a single answer on purpose. Plenty of species pairs are separated by one field mark that a photo may not capture, and a ranked list with an honest confidence score lets you settle the call yourself using the tells below. A tool that always answers with certainty is a tool that is confidently wrong some of the time.

Offline identification: use the app, not this page

This web tool sends your photo to a server, so it needs a working connection. That is usually fine at home and useless on the water, which is exactly where you want it.

The CatchRules app runs the classifier entirely on your device. No upload, no account, no signal required. It identifies a fish at the dock, on the boat, or deep in the backcountry with the phone in airplane mode, and it adds length logging and a catch log on top. If you fish where coverage drops, that is the version worth having.

Field marks that decide the close calls

When two species are genuinely similar, one feature usually settles it. These are the pairs the classifier is asked about most often, and the tell that resolves each.

Channel catfish vs blue catfish

Count the anal fin rays. Channel catfish have 24 to 29; blue catfish have 30 to 36 and a straight-edged fin rather than a rounded one. Spotting fades with age on channel cats, so colour alone misleads.

Largemouth vs smallmouth bass

Look at the jaw. On a largemouth the upper jaw extends past the rear edge of the eye; on a smallmouth it stops beneath the eye. Smallmouth also show vertical bars rather than a horizontal band.

Walleye vs sauger

Check the spiny dorsal fin and the tail. Walleye carry a dark blotch at the rear base of the spiny dorsal and a white tip on the lower tail lobe. Sauger have distinct rows of spots on that fin and no white tail tip.

Bluegill vs pumpkinseed

Read the ear flap. Bluegill show a solid dark flap; pumpkinseed carry a bright red or orange crescent on the rear edge, plus wavy blue lines across the cheek.

King (chinook) vs coho salmon

Open the mouth. Chinook have black gums along the lower jaw and small spots on both tail lobes. Coho have white gums at the base of the teeth and spots on the upper lobe only.

Striped bass vs white bass

Follow the stripes. On a striped bass several lines run unbroken to the tail and the body is long. White bass are deeper-bodied with broken, fainter lines and a single tooth patch on the tongue.

Several of these have a full comparison guide: largemouth vs smallmouth, walleye vs sauger, bluegill vs pumpkinseed, king vs coho, and striped vs white bass.

How to get an accurate identification

  • Shoot the whole fish side-on. A profile view carries the body shape, fin placement, and lateral markings the model relies on.
  • Keep the fish unobstructed. Hands over the flank hide the markings that separate close relatives.
  • Wet fish in good light photograph best; glare and shadow wash out the colour cues that distinguish similar species.
  • If the top result looks wrong, check the alternates. Closely related species are often separated by a single field mark.
  • Photograph the fish before it dries out. Colour drains within minutes of a fish leaving the water, and washed-out flanks cost the classifier the cue it needs most.

What this tool will not do well

Knowing where a classifier struggles is most of knowing when to trust it.

  • Juveniles. Many species do not carry adult colouration until their second year. A young fish photographs as a plausible member of several species at once.
  • Hybrids. Saugeye, splake, and hybrid striped bass sit between two parent species by definition, and the shortlist will usually name both parents rather than the cross.
  • Aquarium and ornamental fish. The model is trained on wild North American species. A tropical pet fish is outside its range entirely.
  • Partial fish. A fillet, a head, or a fish mostly hidden behind a hand carries too little of the body for a confident call.
  • Legal decisions. A photo identification is a hint, not a determination. Confirm the species in hand and confirm the rules with your state or provincial agency before keeping a fish.

Identify by category

Narrowing to a group helps when several species look alike. Each guide covers the field marks that separate them.

Frequently asked questions

How do I identify a fish from a photo?

Upload or take a photo of your catch and the CatchRules classifier compares it against 1,494 marine and freshwater species, returning the most likely matches with a confidence score. A clear side-on shot of the whole fish, unobstructed and in good light, gives the best result.

Is the fish identifier free?

Yes. Identifying a fish on this page is free, requires no account or sign-up, and your photo is processed and then discarded rather than stored. The CatchRules app is also free on iPhone and Android, and adds unlimited identifications, length logging, and a catch log.

Does the fish identifier work offline?

This web tool needs an internet connection, because your photo is sent to a server for classification. The CatchRules app is the offline one: it runs the same classifier entirely on your device, on both iPhone and Android, so it identifies fish with no signal at all, which matters on a boat or in the backcountry.

What fish can it identify?

The classifier covers 1,494 species including bass, trout, salmon, catfish, panfish, snapper, grouper, tuna, sharks and rays, plus crabs, lobsters, and other commonly caught invertebrates. It is trained on wild North American species rather than aquarium fish.

Why did it get my fish wrong?

Three things cause most misses: a photo taken at an angle rather than side-on, a hand or glove covering the flank markings, and juvenile fish that have not yet developed adult colouration. Closely related species separated by one field mark, such as channel versus blue catfish, are the hardest cases. Check the runner-up candidates before accepting the top result.

Is a fish identifier accurate enough to decide what I keep?

No. Treat any photo identification as a strong hint, not a legal determination. Confirm the species by its field marks in hand, and confirm the size and season rules with your state or provincial wildlife agency before you keep a fish.

What happens to my photo?

Your photo is sent to the classifier, scored, and discarded. CatchRules does not store uploaded images, does not attach them to an account, and does not require you to create one to use this page.

How is this different from a general AI image search?

A general image model is trained to describe pictures; this classifier is trained specifically on North American sport fish and invertebrates, so it distinguishes species that differ by fin ray counts or jaw length rather than stopping at “a fish”. Each result also links to a species profile with range and identification notes.

Browse the full species reference

Every species the identifier knows has a profile with range, IUCN status, and identification notes: browse all species, or read the identification guides for the pairs that cause the most trouble.