The four rules that decide "keeper or release"

  • Minimum size limit. The fish must be at least this long to keep. It protects fish until they've had a chance to spawn at least once.
  • Slot limit. Some waters flip the logic: you may only keep fish inside (or outside) a size window — for example 18–27 inches for red drum in many states — protecting the big breeders.
  • Bag limit. How many of that species you can keep per day. Possession limits cap how many you can have in total, including at home in the freezer in some states.
  • Season. Some species can only be kept during certain months; outside the season it's catch-and-release only, or no targeting at all.

How to measure a fish correctly

Most U.S. states measure total length: snout tip to the tip of the compressed tail, fish flat on a ruler, mouth closed. Some species and states use fork length (snout to the fork of the tail) — tunas and some sharks are commonly regulated by fork length. Measuring the wrong way on a fish that's near the limit is one of the most common accidental violations.

Why the rules are so hard to keep track of

Because they change on every axis at once:

  • By species — a 15-inch fish can be a legal walleye and an illegal bass in the same lake.
  • By state and water — the same species can have different limits across a state line, between fresh and salt water, or even between two neighbouring lakes.
  • By date — seasons open and close, and emergency closures happen mid-year.

Traditionally you'd cross-reference a printed regulations booklet or a state website PDF — assuming you know the species, your exact zone and the current year's rules. That's three chances to get it wrong, and fines don't care which of the three you missed.

The two-part problem: a regulations lookup is useless if you've misidentified the fish, and a perfect ID is useless if you don't know the local rules. You need both, together, at the moment of the catch.

Check your local limits in one step with CatchScan

CatchScan showing size limit, bag limit and season for red grouper in Florida state waters
One photo: species ID plus the size, bag and season rules for the water you fished

Fish Identifier: CatchScan is built around exactly that moment. Snap a photo of your catch and the app:

  1. Identifies the species — so the rules you see are for the fish you actually caught (see what fish did I just catch?);
  2. Reads the location saved in your photo — not wherever your phone is now — and matches it to the jurisdiction that governs that water, including whether it was state or federal waters, checked against NOAA boundary data;
  3. Shows the verdict: minimum size, bag limit, season status, and clear keeper-or-release guidance;
  4. Answers follow-ups — "what's the possession limit?", "when does the season close?" — in the same chat Premium.

No booklet, no PDF, no signal-starved state website. One photo, one answer.

Play it safe

Regulations are ultimately set and enforced by your state or provincial fisheries authority, and they can change mid-season. CatchScan gives you the answer at the water's edge; for borderline calls — a fish right at the limit, an unusual zone boundary — confirm with the official source, and when in doubt, release. A released fish is never a violation.