Keepnets, sacks and retaining fish
Tackle · Last reviewed 2026-08-18
Holding a live fish for later is one of the few things an angler does that has a welfare cost with no benefit to the fish — which is why it is regulated more often than almost any other piece of equipment.
Retention is the practice of keeping a caught fish alive in the water until the end of a session or until it can be weighed or photographed, and it is worth a record because it is simultaneously ordinary, regulated and consequential.
WHY IT IS DONE. In match fishing, fish are retained so that a total weight can be recorded and the fish returned together at the end — the alternative would be weighing each fish as it is caught, which is slower and handles the fish more. In specimen fishing, a large fish may be retained briefly in a sack or sling while a camera or a witness is organised. In some fisheries, fish are retained to be taken.
WHY IT COSTS THE FISH SOMETHING. A retained fish is confined, frequently in shallower and warmer water than it chose, in company it did not choose, with reduced water exchange, and it cannot escape contact with the net or with other fish. Scale and mucus damage from net mesh, fin damage from confinement, and oxygen stress in warm shallow water are all documented consequences, and they get worse with time, with temperature, with crowding and with shallow placement.
WHICH IS WHY IT IS REGULATED MORE THAN ALMOST ANYTHING ELSE AN ANGLER CARRIES. A great many fisheries and clubs set rules about whether nets may be used at all, what size and mesh they must be, how many fish may be held, which species may be retained, and whether sacking is permitted. Those rules differ between neighbouring waters and change, and they are a condition of the permit rather than a suggestion — which is exactly the class of thing FishingHQ routes rather than states.
AND THE HONEST SUMMARY IS THAT LESS IS BETTER. Every welfare argument here points the same way: shorter, cooler, deeper, fewer, and not at all where it can be avoided. A fish returned immediately is a fish that has experienced the minimum, and the equipment that makes immediate return possible — an unhooking mat, a large landing net, forceps within reach — is the equipment worth spending on.
- Category
- Nets & landing gear
What it does
Holds a live fish in the water for a period after capture. A keepnet is a long soft-mesh tube staked into the margin and held open by rings; a sack or retention sling holds a single large fish; a weigh sling supports a fish for weighing without hanging it. All of them are confinement, and all of them impose a cost on the fish that rises with time, temperature, crowding and how shallow the water is — which is why every welfare argument about them points towards using them for less time, or not at all.
How to choose one
- Bigger and softer is better in every dimension. A large-diameter net of fine soft knotless mesh damages less than a small one of coarse mesh, and length lets fish spread rather than crowd.
- Knotless mesh is not a refinement. Knots concentrate pressure on scales and mucus, and a great many fisheries require knotless nets for that reason.
- Depth of placement matters as much as the net. A net in deep, cool, moving water is far less stressful than one in a warm shallow margin, and a net lying at an angle with fish forced into one end is the worst arrangement available.
- Time is the variable with the largest effect and the one entirely under the angler's control.
- Warm water raises every cost simultaneously — less dissolved oxygen, higher fish metabolism, more stress — which is why retention in summer is the case with the least justification.
- The rules are set by the fishery and differ between neighbouring waters. Whether a net may be used at all, its mesh and size, how many fish, which species, and whether sacking is permitted are all permit conditions to check rather than assume.
What the numbers mean
Keepnet dimensions are stated in metres of length and centimetres of ring diameter, and both are meaningful: fisheries frequently set minimums for exactly that reason. Mesh is described as knotless or knotted and by mesh size, and knotless is the one that matters. 'Micromesh' and similar terms describe fine soft mesh intended to reduce fin and scale damage and are not standardised. Carp sacks and slings are sized to a fish rather than rated. There is no industry standard behind any welfare claim printed on packaging, which is why fishery rules — which are enforceable — are the more useful guide.
Care, and how it fails
Nets must be dried thoroughly between waters, and this is a biosecurity requirement rather than housekeeping: a wet net moves organisms, eggs and pathogens between fisheries, which is the pathway the check-clean-dry principle exists to interrupt. Some fisheries require dipping. Mesh fails by abrasion and by ultraviolet degradation, and a net with a hole in it will hold fish against the hole. Rings bend and stop the net standing open, which crowds fish into a fold. The most consequential failure has no equipment cause: a net left in shallow warm water for six hours in July, which is a decision rather than a fault.
Where to go next
Where it is used
- Coarse fishingThe discipline in which retention is ordinary rather than exceptional, and where the welfare argument is therefore most worth stating plainly.
- Match fishingRetention exists in its modern form because a competition weighs a total at the end, and almost every rule about nets and mesh was written for that context.
What these connections rest on (2)
Practitioner consensus — 2 connections
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Coarse fishing
Which branch of fishing the equipment or practice sits in.
- Angling Times — Bauer Media (Specialist angling publication)Relied on for: Contemporary UK coarse, match, carp and predator practice as reported by practitioners, including equipment convention and fishery rules on it.FishingHQ's interpretation of what it saysCitation checked — the work exists and is described correctly
- Coarse Fishing — A. & C. Black, 1912 (Specialist angling publication)Relied on for: Classical coarse angling practice: poles, floats, retention and the conventions around them.States this directlyCitation checked — the work exists and is described correctly
Match fishing
Which branch of fishing the equipment or practice sits in.
- Angling Times — Bauer Media (Specialist angling publication)Relied on for: Contemporary UK coarse, match, carp and predator practice as reported by practitioners, including equipment convention and fishery rules on it.FishingHQ's interpretation of what it saysCitation checked — the work exists and is described correctly
- Coarse Fishing — A. & C. Black, 1912 (Specialist angling publication)Relied on for: Classical coarse angling practice: poles, floats, retention and the conventions around them.States this directlyCitation checked — the work exists and is described correctly
Safety reading
What these connections rest on (1)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Handling fish safely
A link from the equipment to the substantial safety topic describing the mechanism it addresses or creates.
- RoSPA water safety information and UK accidental drowning statistics — Royal Society for the Prevention of Accidents (Water-safety or diver-training authority)Relied on for: Accident prevention in angling and around water, including hook injuries and contact with overhead electrical infrastructure.States this directlyPassage read and verified
- Angling Trust guidance for anglers — Angling Trust (Angling or fisheries organisation)Relied on for: Guidance to anglers on handling hooks and tackle safely and on the protective measures commonly recommended.States this directlyCitation checked — the work exists and is described correctly
Rules and access
- Method and bait restrictionsNet size, mesh type, how many may be used and whether sacking is permitted are conditions of a permit far more often than they are matters of preference.
- Size limits and retentionWhether a fish may be retained at all, and which fish, is set by the fishery, the club and in some cases by statute, and it differs between neighbouring waters and changes.
What these connections rest on (2)
Authoritative guidance — 2 connections
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Method and bait restrictions
A link to a rule CONCEPT rather than to a rule. The record carrying it renders the regulatory-variance notice, which is correct wherever the answer is set locally and changes.
- Environment Agency fisheries management, byelaws and rod licensing information — Environment Agency (Government fisheries body)Relied on for: Freshwater fisheries management including byelaws on gear, retention and fish movement, and the biosecurity measures applied to equipment.States this directlyCitation checked — the work exists and is described correctly
- Angling Trust guidance for anglers — Angling Trust (Angling or fisheries organisation)Relied on for: Guidance to anglers on fishery rules and conditions of access, including gear and retention restrictions set by individual waters.States this directlyCitation checked — the work exists and is described correctly
Size limits and retention
A link to a rule CONCEPT rather than to a rule. The record carrying it renders the regulatory-variance notice, which is correct wherever the answer is set locally and changes.
- Environment Agency fisheries management, byelaws and rod licensing information — Environment Agency (Government fisheries body)Relied on for: Freshwater fisheries management including byelaws on gear, retention and fish movement, and the biosecurity measures applied to equipment.States this directlyCitation checked — the work exists and is described correctly
- Angling Trust guidance for anglers — Angling Trust (Angling or fisheries organisation)Relied on for: Guidance to anglers on fishery rules and conditions of access, including gear and retention restrictions set by individual waters.States this directlyCitation checked — the work exists and is described correctly
Environment and conservation
What these connections rest on (1)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Biosecurity: check, clean, dry
An environmental claim attached to the equipment or arrangement that causes it, held to the authoritative standard the predicate requires.
- Check Clean Dry — biosecurity guidance for water users — GB Non-native Species Secretariat (Conservation authority)Relied on for: The pathways by which non-native species and pathogens move between waters on damp equipment, and the check-clean-dry principle developed to interrupt them.States this directlyPassage read and verified
- Environment Agency fisheries management, byelaws and rod licensing information — Environment Agency (Government fisheries body)Relied on for: Fisheries management including fish movement controls, disease and the biosecurity measures applied to equipment.States this directlyCitation checked — the work exists and is described correctly
Check the rules before you fish
Fishing laws, bylaws, access rules, seasons, bait restrictions and permitted methods vary by location and can change. Check the current rules from the relevant authority and the water you intend to fish before fishing.
Check with:
- Current national or regional law for where you are fishing
- Current local bylaws
- The relevant fisheries authority
- The landowner, club or fishery whose water it is
- Any restrictions specific to the species or the method you intend to use
Sources for this page
- Angling Trust guidance for anglers — Angling Trust (Angling or fisheries organisation)Relied on for: Guidance to anglers on fish welfare, retention, handling and the equipment choices that affect them, and on fishery rules governing those choices.States this directlyCitation checked — the work exists and is described correctly
- Humane Harvesting of Fish: percussive stunning and percussive equipment — Humane Slaughter Association (Angling or fisheries organisation)Relied on for: Welfare of caught fish, including the consequences of retention, handling and time out of water.States this directlyNot yet checked
- Angling Times — Bauer Media (Specialist angling publication)Relied on for: Contemporary UK coarse, match, carp and predator practice as reported by practitioners, including equipment convention and fishery rules on it.FishingHQ's interpretation of what it saysCitation checked — the work exists and is described correctly
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: Widely restated descriptions of contemporary tackle convention and its use, recorded as practitioner consensus rather than as scholarship.Background and mechanism onlyCitation checked — the work exists and is described correctly
How FishingHQ labels evidence is explained in the evidence policy.