How to release snapper

It is a common scenario: a group of anglers are in the midst of a red-hot snapper session and someone catches a whopper.

The bin is already full of better-eating-size pannies, and the significance of this larger individual to the breeding stock is noted, the angler pronouncing he would like to release the fish. After a couple of quick pictures the snapper is sent on its way. It gives a couple of kicks and goes down about two metres, but then it slows before floating back to the surface, where it lies belly up and seemingly lifeless.

The stricken fish is retrieved for the fish bin, and back at the ramp, the angler remarks to onlookers checking out the day’s catch: “We tried to let this one go, but she didn’t make it…”

I’m sure most of us have been there before; it’s a fairly common problem, especially when fishing deeper water. If the fish won’t go, the fish won’t go – there’s nothing more that can be done, right? Well, not exactly. When treated correctly, a lot of these ‘dead’ or ‘had it’ snapper can be released in a healthy state. (Some people argue we should kill these big fish, or any fish we catch for that matter, and be done with it. However, discussing the pros and cons of killing versus releasing big snapper is not the thrust of this article.)

If we take a step back and look at what’s actually going on with a belly-up fish on the surface, we will see that the fish is ‘blown’ – a condition that sees its swim bladder over-inflated. This is caused by the gas contained in the swim bladder expanding due to the rapid reduction in pressure that occurs when a fish is brought from the depths to the surface. It’s a simple concept: the deeper the water, the greater the change in pressure; the greater the change in pressure, the more the swim bladder expands and the more it affects the fish.

The swim bladder is quite a fancy organ. In most of the species we catch here in New Zealand, including snapper, the swim bladder is completely closed off to the outside environment. Fish inflate and deflate it via a gas gland, which draws gases out of the blood and into the bladder (and vice versa) to regulate their buoyancy.

I often hear people pronounce, “This snapper is the fattest I’ve ever seen – its gut is bulging!” In reality the gut cavity is full of gas (a mix of oxygen, nitrogen, CO2 and argon), which will do little to make those scales hang lower at the weigh-station.

Unfortunately, snapper cannot regulate the amount of gas in their swim bladders quickly. It can take hours – far longer than the short time available during their rapid ascent on the end of a line. They end up being too buoyant to swim back down under their own power, especially when tired after a fight. The result is a belly-up fish floating weakly on the surface, often barely moving at all.

So is a fish like this stuffed? Well, not really. Fish and many other animals are known to exhibit a behavioural trait know as ‘atonic immobility’, a phenomenon whereby – subject to certain physical cues – they enter a trance-like state of natural and reversible paralysis. It is the reason many fish stop flapping when held upside down.

Atonic immobility has been well documented (Wells et al 2005) in fish held upside-down with pressure applied to the back of the throat (which triggers special receptors). A released snapper, floating belly up on the surface with an over-inflated swim bladder (which often inflates so much that the wall of the stomach pushes out through the mouth and up against the throat) would appear to be subject to the physical cues that trigger atonic immobility.


What this means is that in many cases a snapper that is ‘dead’ and floating on the surface can be perfectly healthy, just a bit buoyant and in a reversible state of paralysis. So how do we overcome these issues when releasing a big snapper?

I know many people who swear by bringing them up slowly, the idea being that this gives time for the fish to adjust to the change in pressure. I’m not going to say these guys are wrong, as the concept is certainly valid. However, I’m not convinced a fish can be brought up slowly enough for this to occur (without taking an hour to wind the fish up). I haven’t personally noticed any difference in fish brought up slowly versus those brought up quickly. The other downside to bringing them up slowly is that a long fight can lead to an exhausted fish being too tired to swim back down, even if it’s only slightly buoyant.

Another remedy some may be familiar with, is popping the swim bladder to expel excess gas. This is a good option and usually fixes the buoyancy issue fairly promptly, allowing a fish to swim back down under its own power. A major issue with this technique, however, is that most people don’t do it properly and end up popping the gut cavity with a grubby bait knife, or piercing the stomach, which is poking through the mouth.

Before I go any further, the thing that sticks out of a blown snapper’s mouth is not its swim bladder. It is the stomach pushed out by the inflated swim bladder. Popping it will expel some of the air in the swim bladder, but you pierce the stomach at the same time – less than ideal. The fish has been put under enough stress already and doesn’t need to deal with stomach juice leaking into its gut cavity, along with the risk of infection.

The only way to properly ‘vent’ (expel gas from the swim bladder) a snapper is by inserting a clean hypodermic needle through the side of the fish and directly into the swim bladder itself. It’s not a terribly tricky procedure once you know what you are doing.

Next time you are filleting a snapper, take note of where the swim bladder is located – it is always right at the top of the gut cavity. It’s easy to locate on a whole live snapper, as it is roughly in line with the pectoral fin when it’s laid flat along the fish’s side. You can also feel the swim bladder by running your hand down the side of the fish and feeling for where the denser muscle meets the softer gut wall. The best place to insert the needle is about halfway along where the pectoral fin lays flat and slightly down from the top of the gut cavity.

So with a snapper intended for release, the needle is gently inserted through the gut cavity wall, and it is simply a case of cradling the snapper upright in the water and letting the gas bubble out from the needle. There can be a lot of gas in a big snapper, and it may take several minutes to get it out. I try to get as much out as possible, but you will never remove it all; gentle pressure applied to the side of gut cavity can help.

Once the gas is removed, the fish can be released. It should be cradled upright in the water and given time to revive. Face it into the current if possible to help water flow over its gills. Don’t go yanking a fish backward and forwards by the tail – fish like snapper don’t swim backwards and are not adapted to cope with water flowing over their gills that way either. Hold the fish still and let it pump water over its gills itself.

It’s easy to tell if the fish is healthy: the fins should be erect and I always look at the eye. The eye will be looking down if in a healthy state, rather than centered. With a gentle push, the fish will swim down, upright and under its own power.

The needle-venting method is commonly used for venting fish kept for aquaria, and has even been used to successfully keep alive hapuku taken from as deep as 120m. When done properly, it is relatively unobtrusive, and going by fish kept in captivity subject to this venting, they survive the procedure just fine.

With a deflated swim bladder, the fish can be somewhat negatively buoyant when it returns to where it was taken from. However, based on observations of fish kept in captivity, the pinprick hole in the swim bladder heals rapidly, and the fish is back to normal buoyancy within a day or so.

Another good option for releasing blown fish is the drop-weight method. It is perhaps a better system for those not practiced in the needle method. All that is required is a length of light rope or heavy line, a barbless J-hook and several kilos of lead (dive weight, sinkers etc). The lead is attached via a short length of line to the eye of the J hook and a longer length of line to the bend in the shank. The barbless hook is placed through the bottom jaw of the fish, the fish lowered to bottom, and with a gentle tug on the line, the fish is set free. Downsides of the drop-weight method are that it can take a lot of lead to get a larger fish down. Also, the drop-weight really needs to be set up prior to fishing and is nowhere near as portable as a needle in the tackle bag (which is handy if you fish on a lot of different boats).

Both methods will dramatically increase the survival of fish released in deep water. However, as with releasing any fish, a few good practice rules still apply. They are all no-brainers, yet they seem to be overlooked by a large number of fishermen:

•Don’t gaff a fish intended for release.
•Keep the fish out of water for the minimum length of time. Fish landed and released quickly often swim down no problems, even when blown, although exhausted fish held out of the water for a while will almost always need venting and reviving.
•Photos are fine, but have the camera ready first – and again, be quick!
•Support the entire weight of the fish out of the water. Never lift it by its tail or eye sockets, and never ever stick your hands in its gills! If you must weigh your fish, weigh it in the net or a purpose-built weighing sling rather than hanging it by it its jaw or tail, as this can case serious damage to the backbone.
•Wet your hands/arms/t-shirt/rags or whatever you use to touch the fish.
•If you use a net, the rubber-meshed variety is much kinder to a fish’s skin and won’t damage fin rays and split fins to the same extent.

Finally, remember photos last longer than fillets, and a fish in the water is a fish for the future!


Wells R.M.G., McNeil H., MacDonald J.A. (2005). Fish hypnosis: Induction of an atonic immobility reflex, Marine Freshwater Behaviour and Physiology, Vol 38 (1): 71-78.



This article is reproduced with express permission of
Josh Worthington
by Josh Worthington - 2011
Re-publishing elsewhere is prohibited

Originally published in New Zealand Fishing News



Releasing big snapper that have been caught from deeper water and become embolised or ‘blown’, can take a little effort. (Photo: Geoff Muir)

A wet towel is a good way to restrain a fish for unhooking with minimal damage to slime and skin. (Photo: Sam Mossman)

Venting fish with a hypodermic needle can be aided by gentle pressure to the side of the belly cavity. Right: Hypodermic needles that can be used for venting fish. (Photo: Geoff Muir). These were purchased from a veterinary supply shop.
(Photo: Sam Mossman)


A simple ‘drop-weight’ rig that can be used as an alternative to venting.

The writer vents a snapper before release.
(Photo: Geoff Muir)

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