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.
Telling juveniles from adults underwater
Explainer · Last reviewed 2026-08-25
Juveniles frequently differ from adults in colour, pattern, proportion and habitat — sometimes enough to look like another species entirely — and they are exactly the fish a size limit exists to protect.
Safety
Fish welfare — Can cause injury needing treatment
Juveniles of many species look nothing like the adults, and several are magnified into looking like a takeable adult of a smaller species. Taking immature fish removes animals before they have bred, which is the specific harm minimum sizes exist to prevent.
What reduces it: Learn the juvenile forms of the species you are likely to meet, not only the adults. Where a fish's life stage is uncertain, do not shoot — the size limit is a proxy for maturity and a diver who is unsure of the stage is unsure of the size.
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.
A juvenile fish is not a small adult, and treating it as one is the identification error most likely to end with an undersized or protected fish on a shaft.
WHAT CHANGES WITH AGE.
COLOUR AND PATTERN. Many species carry entirely different juvenile liveries — bars, ocelli, blotching, or colours the adult never shows. In some groups the juvenile is more strikingly marked than the adult, which is disorienting for anybody who learned the species from an adult photograph.
PROPORTION. Juveniles usually have relatively larger eyes and heads and a shorter, deeper body than the adult of the same species. Because proportion is one of the characters that survives underwater, this directly corrupts a character a diver was relying on.
FIN SHAPE. Fins that are rounded in a juvenile can become elongate or filamentous in an adult, and the reverse occurs too.
HABITAT. This one is easy to miss and it is often the most useful clue. Many species use different habitat as juveniles — shallower, more structured, more sheltered: seagrass, kelp holdfasts, estuarine margins, rubble, mangrove where present. A fish in juvenile habitat is more likely to be a juvenile, and encountering an unfamiliar-looking fish in a nursery habitat should raise the possibility rather than suggest a new species.
BEHAVIOUR. Juveniles of species that are solitary as adults are often in groups, and are frequently less wary — which is precisely what makes them approachable, and therefore vulnerable.
WHY IT MATTERS BEYOND THE RULE. Size limits are usually set so that fish have an opportunity to spawn at least once before they can be taken. A fish removed before maturity has contributed nothing to the next generation, which is a different and larger loss than the same fish taken later. That reasoning does not depend on any particular jurisdiction's number, and it is the reason the limit exists rather than a bureaucratic detail attached to it.
Two failures at once
The juvenile problem is dangerous because it breaks two rules simultaneously.
IT BREAKS IDENTIFICATION, because a juvenile may not look like the species it is — and may look like a different species that is legal, or protected, or simply absent from the diver's expectations.
IT BREAKS SIZE JUDGEMENT, because refraction already inflates apparent size and juveniles are by definition near the limit where that error changes the answer. A juvenile that looks marginal is very likely well under.
And the two errors compound rather than cancel. A diver who has misidentified the species is applying the wrong size rule to a fish whose size they are overestimating.
The response is the same as the family's general rule, applied earlier: a fish that looks small for its apparent species, or that is in nursery habitat, or that does not match the adult you expected, is a fish to look at rather than to shoot. A juvenile that cannot be matched to an adult you know is an uncertain identification, and the rule for those does not soften because the fish is small — IF IDENTIFICATION IS UNCERTAIN, DO NOT TAKE THE FISH. Looking at juveniles carefully is also how a diver learns the local community, which pays back over years.
Authoritative guidance
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
- 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: That juvenile forms may differ substantially from adults in colour, pattern and proportion, and that identification guides distinguish them.States this directlyCitation checked — the work exists and is described correctly
The other end of the size question
Size rules mostly protect small fish, and the ecology does not stop there.
In many species the largest individuals are disproportionately productive spawners: fecundity rises steeply with body size, and in some groups the eggs of larger females are also more viable. A single very large fish can be worth many average ones to the population, which is why maximum size limits and slot limits exist in some fisheries alongside minimum ones.
That cuts directly against the instinct of a hunter. The largest fish is the one everybody wants and the one a diver will swim past several smaller ones to reach.
FishingHQ does not resolve this by telling anybody what to shoot. What it will say is that a diver choosing a mid-sized mature fish over the largest one present is making a defensible ecological choice, that the argument for it is documented rather than sentimental, and that spearfishing is one of the very few methods where the choice is genuinely available at all. What is done with that is the diver's, within whatever rules apply — and those rules, including any maximum or slot limits, are held by the local fisheries authority and not by this platform.
Scientific evidence
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
- ICES Advice on fishing opportunities, catch and effort — International Council for the Exploration of the Sea (Scientific institute)Relied on for: Stock assessment and management advice reflecting the contribution of large mature individuals to reproductive output.Background and mechanism onlyCitation checked — the work exists and is described correctly
- Good Fish Guide — Marine Conservation Society (Conservation authority)Relied on for: Assessment of stock and method sustainability, including the role of size and maturity in harvest choices.Background and mechanism onlyCitation checked — the work exists and is described correctly
Where to go next
Where it matters
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.
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
The case where an identification failure and a size failure happen together.
- 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
Water and ground
What these connections rest on (1)
Scientific evidence — 1 connection
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
Estuary
The habitat record and the age-class intelligence that belongs to it.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Species habitat association, depth range and feeding ecology across marine fishes.Background and mechanism onlyPassage read and verified
Related 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.
Lookalike species, and why uncertainty means do not shoot
The specific case and the general rule it falls under.
- 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
More explainer
Not related to this page — just the rest of the section, because this record connects to very little and a short page should still lead somewhere.
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
- 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: Juvenile and adult identification characters, and their differences.States this directlyCitation checked — the work exists and is described correctly
How FishingHQ labels evidence is explained in the evidence policy.