Fish size limits are the legal length rules that decide which fish you can keep and which must go back. State wildlife agencies set them for inland and nearshore waters; federal agencies set them offshore. A fish that misses the mark by half an inch is not a legal fish, and the way you measure it has to match the way an enforcement officer would measure it. Get the method wrong or the length wrong, and a good day on the water turns into a citation, a suspended license, or in federal waters, something far worse.
What Size Limits Actually Require
Three types of size rules cover almost every regulated species, and each one exists to protect a different part of the population.
Minimum Size Limits
A minimum size limit means the fish has to be at least a set length to keep. Anything shorter goes back. The point is to let fish spawn at least once before they enter the harvest. This is the most common form of size regulation and the one most anglers run into.
Maximum Size Limits
A maximum size limit works the other way. If the fish is longer than the cap, you release it. The largest fish in a population tend to be the most productive spawners, producing more eggs with better survival than younger fish, and pulling them out destabilizes the population faster than taking smaller ones. Some agencies treat harvesting an over-maximum fish the same as poaching.
Slot Limits
Slot limits define a size window. A protected slot requires you to release any fish inside the window while allowing you to keep fish above or below it. A harvest slot flips that: you may only keep fish within the window. Protected slots are the more common of the two and typically shield the mid-sized fish approaching peak reproduction.
Specific numbers vary by species and by state, and rules typically update every year. A limit that was legal last season may not be legal this one, so check the current regulation for the water you’re fishing before you go.
How to Measure a Fish the Right Way
Regulations name a specific measurement method for each species, and enforcement officers use that method during inspections. If your fish doesn’t measure up under theirs, yours doesn’t matter.
Total Length
Total length runs from the tip of the snout, with the mouth closed, to the very end of the tail fin, with the tail lobes squeezed together to capture the maximum reading. It’s the default for most freshwater species and many saltwater species.
Fork Length
Fork length runs from the tip of the snout to the center of the “V” where the tail splits. Agencies use it for species with deeply forked tails whose outer tips break or wear easily, because a chipped tail lobe would shorten a total-length reading and misrepresent the fish’s real size.
Lower Jaw Fork Length
Lower jaw fork length is used almost exclusively for billfish like marlin and sailfish. You start at the tip of the lower jaw and measure to the center of the tail fork. The bill is excluded because it would dramatically inflate the reading. If you’re fishing billfish in federal waters, this is the measurement that governs.
Technique That Matches Enforcement
Lay the fish on a flat, hard surface or a measuring board with the body fully extended so the spine is straight. Any curve shortens the reading. Press the closed mouth against the headstop; an open mouth adds length that doesn’t count, and an officer will close it during inspection regardless of how you measured on the boat. For total-length species, pinch the tail lobes together and read at the farthest point. For fork-length species, read at the innermost point of the fork.
A few things experienced anglers learn the hard way. Wet the surface first so the fish slides into position without stripping its slime coat. Don’t stretch the fish or push the tail beyond its natural extension. Measure before you put the fish on ice, since cold storage can cause slight shrinkage that pulls a borderline-legal fish under the line.
Who Sets the Rules Where You Fish
Different agencies own different waters, and the rulebook shifts as you move offshore.
State Waters
State wildlife and fisheries departments set the size limits, bag limits, and seasons for inland waters and nearshore coastal areas. State game wardens are the officers you’ll meet on lakes, rivers, and inshore saltwater. They can inspect your catch, measure your fish, check your license, and cite you on the spot.
Federal Waters
Once you move into the Exclusive Economic Zone, which extends from 3 to 200 nautical miles offshore, federal regulations take over. Eight regional fishery management councils develop the specific management plans, including size and bag limits, and NOAA Fisheries implements and enforces them under the Magnuson-Stevens Fishery Conservation and Management Act, the primary federal law for marine fisheries in U.S. waters.1NOAA Fisheries. Magnuson-Stevens Fishery Conservation and Management Act Enforcement offshore comes from NOAA’s Office of Law Enforcement and the U.S. Coast Guard, both at sea and at the dock.
What a Violation Costs You
Penalties for keeping a fish outside the legal size range run from a modest state fine to consequences that end a commercial career. The rules are simple enough that enforcement officers give very little benefit of the doubt.
State Fines and License Suspension
State penalties for possessing undersized or oversized fish vary widely. Most states impose per-fish fines, and repeat offenders face steeper penalties, gear seizure, and suspension of fishing privileges. A conviction can also travel through the Interstate Wildlife Violator Compact, an agreement among the majority of U.S. states under which a suspension in one member state triggers suspension in every other member state. A short fish kept on a vacation trip can cost you the ability to fish at home.
Federal Civil Penalties
Federal violations hit harder. Under the Magnuson-Stevens Act, civil penalties can reach up to $100,000 per violation, and each day of a continuing violation counts as a separate offense.2Office of the Law Revision Counsel. 16 USC 1858 – Civil Penalties and Permit Sanctions Knowing violations can also bring criminal charges. NOAA can revoke or suspend federal fishing permits on top of any monetary penalty, which can effectively end a commercial operation.
Vessel and Gear Forfeiture
Federal law authorizes the government to seize any fishing vessel, along with its gear, cargo, and stores, used in connection with a prohibited act under the Magnuson-Stevens Act.3Office of the Law Revision Counsel. 16 USC 1860 – Civil Forfeitures All fish found on board a seized vessel are presumed to have been taken illegally, and the owner carries the burden of proving otherwise. Recreational anglers in federal waters face the same forfeiture risk, though enforcement discretion means smaller-scale violations more often end in fines.
The Lacey Act Trap
An angler who catches undersized fish in violation of a state’s rules and then transports them across state lines may also face federal prosecution under the Lacey Act, which makes it illegal to import, export, transport, sell, or acquire any fish taken in violation of state, tribal, or foreign law.4Office of the Law Revision Counsel. 16 USC 3372 – Prohibited Acts A state misdemeanor for an undersized bass becomes a federal offense the moment the fish crosses a state line. Anglers fishing border waters or traveling to tournaments get caught by this more often than they expect.
Releasing a Fish That’s Outside the Limit
A fish that falls outside the legal window goes back, but tossing it carelessly defeats the purpose of the rule if the fish dies. Proper release is a practical obligation and, in some jurisdictions, a legal expectation.
Handle the fish as little as possible and keep it in the water when you can. Wet your hands before touching it to protect the slime coat, avoid squeezing the body, and stay away from the gills. Use long-nosed pliers or a dehooking tool to back a hook out. Circle hooks, which tend to catch in the corner of the mouth rather than deep in the throat, make release far easier and are required for certain species in some fisheries.
Barotrauma and Deep-Water Release
Fish brought up from deep water suffer barotrauma. The rapid pressure change causes the swim bladder to expand, which can push the stomach out through the mouth, bulge the eyes, and leave the fish unable to swim back down on its own. A barotrauma-affected fish dropped over the side usually floats on the surface and dies.
Two tools address this. A descending device is a weighted clip or cage that carries the fish back to depth, where pressure re-compresses the swim bladder and the fish swims off. A venting tool is a hollow needle that punctures the body wall to release trapped gas. Descending devices are generally considered safer for the fish because they don’t create a wound. Federal reef fish regulations in the Gulf of Mexico previously required anglers to carry one of these tools rigged and ready under the DESCEND Act, though those specific requirements expired in January 2026.5NOAA Fisheries. NOAA Fisheries Reminds Reef Fish Fishermen of DESCEND Act Requirements and Announces a Final Rule to Clarify Descending Device and Venting Tool Definitions for Reef Fish Fishing Carrying a descending device is sound practice any time you’re fishing deeper than about 50 feet. Some officers will count a dead release against your bag limit.