Before you spearfish — this comes first
- Get proper instruction before you spearfish. A recognised freediving or spearfishing course teaches the things that actually kill people in this sport, and reading about them is not the same as being taught them.
- Dive with a buddy, and dive one up, one down — one diver in the water, one on the surface watching them, every dive. A breath-hold blackout is silent and gives no warning; a watching buddy is the difference between an incident and a fatality.
- Stay inside your own training and experience. Depth and breath-hold times are personal, they change day to day, and nobody else's numbers apply to you.
- Understand the conditions before you enter the water: visibility, current, swell, tide, boat traffic and your exit. Conditions decide whether a dive is reasonable far more often than skill does.
- Use equipment you have been shown how to use, check it before every session, and be visible — a marked float and line are how boat traffic knows you are there.
- Never extend a dive for a fish. No catch is worth pushing a breath-hold, and the urge to take one more second is exactly what a blackout feels like from the inside — which is to say, like nothing at all.
Identifying fish underwater
Explainer · Last reviewed 2026-08-10
The one skill spearfishing genuinely requires that angling does not — because the decision to take a fish is made before it is caught, not after.
Safety
Venomous and spined species — Can cause injury needing treatment
Misidentification underwater is not only a legal and welfare problem. Several of the fish most easily confused at a glance — scorpionfish, weevers, stonefish, some rockfish — carry venomous spines, and the injury usually happens when the fish is handled after being taken rather than when it is shot.
What reduces it: Identify before shooting rather than after landing, know which venomous species occur where you dive, and handle any unfamiliar fish with the assumption that it is spined. Gloves reduce punctures and do not prevent them.
Fish welfare — Can cause injury needing treatment
A fish that cannot be identified with confidence and is shot anyway may be a protected species, an undersized individual, or an animal outside a season. None of those can be undone once the shaft is through it.
What reduces it: Treat uncertainty as a refusal rather than as a risk to weigh. The whole selectivity argument for this discipline depends on the decision being made before the trigger.
Precautions that always apply here
- Never spearfish or freedive alone.
- Dive one up, one down: one diver down, one on the surface actively watching, every single dive.
In angling, identification happens after the fish is landed, and a mistake can usually be corrected by returning it. In spearfishing it happens before the shot, in a few seconds, underwater, on a moving animal, through a mask, with colour distorted by depth — and the decision is irreversible.
That makes underwater identification a skill with no equivalent in rod fishing, and it is the reason a spearfisher's obligation to know the local fauna is stronger than an angler's. Protected species, size limits, closed species and species that are simply not worth taking all have to be recognised in the water.
Depth complicates it in a specific, learnable way. Water absorbs light from the red end of the spectrum first, so red disappears within a few metres, then orange, then yellow. A fish that is unmistakably red at the surface is grey at fifteen metres. Anyone identifying by colour is identifying by a variable that changes with depth, which is why shape, fin arrangement, proportion and behaviour are the reliable characters — the same characters FishingHQ's species records lead with, for the same reason.
The honest rule that follows is short: IF YOU CANNOT IDENTIFY IT, DO NOT SHOOT IT.
Why colour is the least reliable character underwater
Water absorbs light selectively, and it does it fast. Red is essentially gone by about five metres, orange follows, then yellow, leaving the blue-green end of the spectrum. A torch restores the colour locally, which is why a photograph taken with flash at depth looks nothing like what the diver saw.
The consequence for identification is that colour-based characters — the red fins of a perch, the orange spots of a plaice, the red iris of a roach — become unavailable at exactly the depths where a decision has to be made. Two species that are obviously different at the surface can be near-identical grey shapes at twenty metres.
So the characters worth learning are the ones that survive: overall body shape and depth-to-length proportion; the number, position and separation of the dorsal fins; the shape of the tail; the position of the mouth; and behaviour, which is frequently the most diagnostic of all — how a species holds in the water, whether it schools, whether it approaches or retreats.
This is also why FishingHQ's species records put fin arrangement and proportion first in their identification lists and colour last. It reads as a stylistic choice on a page. Underwater it is the difference between a usable identification and none.
Scientific evidence
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
- The Fishes of the British Isles and North-West Europe — Macmillan, 1969 (Reference work)Relied on for: That morphological characters — fin arrangement, proportion, mouth position — are the reliable basis for species separation, as distinct from colour.FishingHQ's interpretation of what it saysCitation checked — the work exists and is described correctly
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Species-level morphological descriptions used for identification.Background and mechanism onlyPassage read and verified
Where to go next
Where it matters
- Reef spearfishingOn reef the question is almost never whether there is a fish. It is which fish, whether it may be taken, and whether it should be — and all three are answered before the shot or not at all.
- SpearfishingIdentification before the shot is the mechanism behind the discipline's selectivity claim, and the point at which its welfare and regulatory obligations are met or missed.
What these connections rest on (2)
Practitioner consensus — 1 connection
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.
Reef spearfishing
A practitioner claim linking the environment to the discipline's one genuinely distinctive skill.
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: Widely restated practitioner guidance on declining shots where identification is uncertain.Citation checked — the work exists and is described correctly
- Good Fish Guide — Marine Conservation Society (Conservation authority)Relied on for: That knowing what a fish is precedes any judgement about whether to take it.Citation checked — the work exists and is described correctly
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Spearfishing
A membership assertion rather than a topical one: this record teaches the discipline or its equipment, so the discipline's mandatory safety posture applies to it.
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Breath-hold spearfishing as a defined discipline with its own technical, equipment and safety standards, set out by the international underwater federation.States this directlyCitation checked — the work exists and is described correctly
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: That the safety requirements of breath-hold diving apply across the discipline rather than to particular equipment or techniques within it.States this directlyPassage read and verified
Gear this affects
What these connections rest on (1)
Practitioner consensus — 1 connection
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.
Shafts and tips
A practitioner claim linking equipment choice to the identification skill the discipline uniquely requires.
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: Widely restated practitioner guidance on declining shots where identification is uncertain.Citation checked — the work exists and is described correctly
- Good Fish Guide — Marine Conservation Society (Conservation authority)Relied on for: That knowing what a fish is precedes any judgement about whether to take it.Citation checked — the work exists and is described correctly
Related reading
- How fish seeUnderwater identification depends on what light survives at depth.
- Reading underwater conditionsWater absorbs red light within a few metres, so colour — the character most people identify fish by — is unavailable at exactly the depths where the decision is made.
What these connections rest on (2)
Scientific evidence — 2 connections
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
How fish see
Underwater identification depends on what light survives at depth.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Species and habitat data underlying this connection. Underwater identification depends on what light survives at depth.States this directlyPassage read and verified
Reading underwater conditions
A claim about the physics of light in water with a direct practical consequence, held to a scientific standard.
- The Fishes of the British Isles and North-West Europe — Macmillan, 1969 (Reference work)Relied on for: That morphological characters rather than colour are the reliable basis for species separation.FishingHQ's interpretation of what it saysCitation checked — the work exists and is described correctly
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Species-level morphological descriptions used for identification independent of colour.Background and mechanism onlyPassage read and verified
How this compares
- How visibility changes everythingPoor visibility removes the characters an identification depends on at the moment a shot decision is made.
- Identifying fish by shape when colour is goneOne record ranks the characters; this one asks which of them survive the water between the diver and the fish.
- Low-volume masks, and why volume mattersField of view is the trade for low volume, and it is what a hunter uses to find fish.
What these connections rest on (3)
Authoritative guidance — 3 connections
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
How visibility changes everything
Why reduced visibility should raise the shot threshold.
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance on visibility, buddy separation and conditions assessment.States this directlyCitation checked — the work exists and is described correctly
Identifying fish by shape when colour is gone
The existing identification record and the underwater reordering of it.
- FAO Species Identification Guides for Fishery Purposes and the FAO Species Catalogues — Food and Agriculture Organization of the United Nations (Scientific institute)Relied on for: Identification by ranked diagnostic characters, and the limits of identification from general appearance.States this directlyCitation checked — the work exists and is described correctly
Low-volume masks, and why volume matters
The cost of the design, expressed in what it makes harder.
- AIDA International freediving education and safety standards — AIDA International (Water-safety or diver-training authority)Relied on for: Freediving equipment standards including mask volume and equalisation.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.
Selectivity and what it is used for
Selectivity is realised only where the diver can actually identify the fish.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Diver safety guidance underlying this connection. Selectivity is realised only where the diver can actually identify the fish.States this directlyPassage read and verified
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