An angler holding a fish in the water before release. Photo via Pexels.
Catch and release is a conservation practice, not a guarantee. Released fish suffer delayed mortality, and the factors driving it are well studied and largely avoidable.
Air exposure
Gills are designed to extract oxygen from water and collapse in air. Time out of water is one of the strongest predictors of whether a released fish survives, and it interacts with temperature: a study of brook trout found that air exposure beyond 30 seconds combined with water above about 19.5°C produced a synergistic rise in reflex impairment, with fish over about 330 mm sensitive to exposures beyond 10 seconds.
The practical standard is to keep the fish in the water while unhooking wherever possible, and if it must come out, to keep that time as short as holding your own breath comfortably. The thresholds are species-specific — a USGS study of Yellowstone cutthroat found exposures of 60 seconds or less were unlikely to be a concern — so the conservative number is the one to work to.
Handling
Fish are covered in a slime layer that resists infection. Dry hands, dry cloth and dry surfaces strip it.
Wet hands before touching. Avoid squeezing behind the gill plates, which damages the heart and gills. Support the body horizontally rather than holding a heavy fish vertically by the jaw, which can damage the spine and jaw structure.
Hooking location
A fish hooked in the lip survives at far higher rates than one hooked deep in the throat or gills.
This is why regulations sometimes specify hook types. Circle hooks tend to rotate and catch in the corner of the mouth, and are frequently mandated in fisheries with high release rates. Barbless hooks, or barbs pinched down, come out faster and cause less tearing.
If a fish is hooked deeply, cutting the line close is generally better than extraction. Many hooks corrode or are shed.
Water temperature
Warm water holds less dissolved oxygen, and a fish fighting in warm water accumulates lactic acid it may not recover from. Work on largemouth bass found impairment stayed low where fight times were kept under two minutes and air exposure under 30 seconds — fight duration matters as much as handling.
This is the reason for hoot-owl restrictions — closures that prohibit fishing during the warmest afternoon hours on trout streams in summer. They exist because release mortality climbs sharply above certain temperatures.
The practical version: if the water is unusually warm, the responsible choice is often to stop fishing rather than to fish carefully.
Reviving
Hold the fish upright, facing into gentle current, until it swims off under its own power. Do not move it back and forth — that forces water the wrong way through the gills.
Gear that improves the odds before the fish is landed
Most of what determines survival is decided before the fish reaches your hand.
Playing a fish to complete exhaustion is the single largest controllable factor after hooking location. Heavier tippet or line than feels sporting shortens the fight, and a short fight leaves a fish with the physiological reserves to recover. Light tackle is the more demanding way to fish and the harder one on the fish.
A rubber or rubber-coated net does far less damage to the slime layer and to fins than knotted mesh, and it does not tangle hooks, which shortens handling. Barbless hooks come out in a motion rather than a procedure.
Pliers or forceps within reach beat fingers in a mouth, and a hook remover designed for deep hooks is worth carrying if you fish bait. The gear that shortens the interval between landing and release is the gear that matters.
Reading a fish that is not recovering
A fish held upright in gentle current should begin working its gills and then resist your hand. Both signs need to appear before it is released.
A fish that rolls, drifts sideways or floats is not ready, and releasing it there usually means it dies out of sight. Continue supporting it, keep water moving over the gills from front to back, and give it longer than feels necessary — recovery can take several minutes after a hard fight in warm water.
Never move a fish back and forth in still water. Water has to flow over the gills in one direction; pushing it backwards forces water the wrong way through them and does harm rather than good. In still water, move the fish forward slowly in a figure of eight, or hold it facing into whatever current exists.
Sources
- Bouyer et al., Identifying thresholds in air exposure, water temperature and fish size that determine reflex impairment in brook trout exposed to catch-and-release angling (PMC)
- US Geological Survey, Effects of air exposure on survival of Yellowstone Cutthroat Trout angled from a stream with warm water temperatures
- The influence of water temperature and fight intensity on physiological stress and reflex impairment of angled largemouth bass (PMC)
This article was researched and drafted with the assistance of AI tools and reviewed, fact-checked and edited by Leonidas Clark before publication. Regulations vary by water and change in season; confirm with the managing agency before you fish.
