Fish Processing
  |  First Published: July 2012

You are what you eat, and the quality and edibility of the fish you bring home says a lot about you. Treating the fish so that it tastes as good as possible, and stays fresh for longer, displays admirable skill and shows respect for the fish. And when you consider all the time and effort you put in to catch a few keepers – and the strict bag limits in force these days – proper fish care is just plain common sense.

Fortunately, the basics of fish care are pretty straight forward. In this article I'll explain the science, the law and address a furphy or two.


The traditional method of processing a fish is to bleed it (depending on the species) and immerse it in a brine slurry. However, more anglers are now opting to keep their fish alive in a livewell so they can process their catch later. This can be a good option, but there are some regulations to bear in mind if you want to do this.

First of all, it’s illegal in Queensland to retain live coral reef fin fish. The only exceptions are if you’re planning to put the fish in an aquarium, or if you intend to immediately return it to the sea.

Second of all, it can be a legislative minefield to fillet or remove the head of fish in Queensland until you get them ashore. The minimum length of a fish fillet that can be carried aboard your boat is 40cm, and the skin and scales have to be left on. You also can’t return a fillet to the boat after it’s been taken ashore. There are some exceptions to the rule, and you can find out more at www.dpi.qld.gov.au/28_3054.htm.

Because of the hassle involved in adhering to these on-water filleting regulations, most offshore crews simply ice all the fish down and leave processing until they get ashore. This saves confusion and constant referral to the rule book.


When storing unfilleted fish, there has been a lot of discussion about whether or not to leave the gut in. The theory is that the less flesh that gets exposed to the air the better (and that scales serve as a form of protection to the outer surface). Likewise, because an un-gutted fish will be thicker, it will be less susceptible to freezer burn and therefore last longer.

Unlike hot-blooded animals where the gut is removed to get rid of the heat, fish are cold-blooded. That means when they’re immersed in a cold environment, the low temperatures will generally control bacterial growth.

Having said that, gutting and gilling breaks the skin and risks exposing the fish to bacteria that can spoil the flesh. The decision of whether to gut or not is just one you’ll have to make yourself.


Adding salt to a slurry of ice and water (or using a seawater and ice brine) lowers the temperature at which the water freezes. Salt makes ice melt more slowly, and the temperature of the water will drop. The end result is a saltwater brine in a two-phase (liquid and solid) mixture that quickly chills down fish.

Fish cools faster in an ice slurry because there are no air pockets, as there would be with just party ice. The maximum surface area in direct contact with the fish, combined with the super-cold water, means there is a faster heat transfer from the fish to the ice.

Why go to the trouble to make your fish chill faster? Because you want to stop bacterial growth as quickly as possible. Your slurried fish will quickly reach a temperature that inhibits bacterial growth, and the quicker the fish is cooled, the longer it will stay fresh.


Iki jime (brain spiking) is a humane and efficient way of killing your catch as well as preserving the flesh. A struggling fish can cause bruising of the flesh if it flops around on the deck.

Place a stiff knife/spike or curved iki jime tool into the brain through the top of the head. Most fish’s brains are located at the top of the head near the eyes, but on some small fish insert the spiking tool either through the gill arch underneath the brain or at the posterior end of the eye socket. Sites such as www.youtube.com have diagrams to give you an idea of where to insert the spike. You’ll be able to tell when you’ve hit the right place when the fish flutters and shudders.


Bleeding the catch straight away helps keep the flesh in good condition and prevents strong blood lines through the fillet.

To keep the fish intact while bleeding it, slit the throat with a knife, shears or a pair of scissors. I use pointed scissors that are closed and simply stab their point in from low in the gill opening and angled up behind the gills to cut the main artery. The scissors are less dangerous than a knife blade and their handle reduces the risk of slippage and cuts to your hands or fingers.


Once you’re ashore and have filleted your catch, you can either cling-wrap/zip-lock the fillets and put them in the fridge, or airtight vacuum seal them and pop them into the freezer.

When camping, a portable fridge/freezer makes life much easier. If you plan on eating the fish within the next couple of days it will be perfectly fine in the fridge (1-4oC). Otherwise, store below -18oC in the freezer but do not refreeze once defrosted.


If the fish is going to be frozen for anything longer than a couple of weeks, I store my fillets in vacuum sealed freezer bags. I've found that when airtight and vacuumed sealed (air-removed) they store in the freezer a lot longer.

If you don't remove the air then your fillets will most likely get freezer burn. I've seen incorrectly handled prime red reef fish develop freezer burn within mere weeks when the fillets were stored in packaging that had trapped air inside.

A domestic model vacuum sealer is available from most electrical retail outlets.


Despite the common belief that red gills/clear eyes is a sign of the freshest fish, I think this is very much a furphy.

As soon as your fish hits the water in the esky the gills will start to brown and the eyes will most likely start to go milky. This is absolutely normal and despite marketing to the contrary, brown gills and milky eyes is not necessarily a sign that the fish should be avoided.

Another example, are the deepwater line-caught fish that come up with their eye's ‘popped’ and as bloodshot as road maps. These fish are some of the best eating in the sea.

Red gills and clear eyes can be achieved or ‘preserved’ by chemical additives in the ice slurry, which some people can be allergic to. Likewise, prawns (and some squid) are usually treated with a 1% sodium metabisulphite solution to prevent black spot - I know people who react to commercially processed prawns yet have no problem with fresh caught prawns. Some anglers also believe that these additives make prawns and squid unsuitable (or less successful) for use as bait.

Whatever the truth is, if you bleed, brain spike, slurry and vacuum seal then you can rest assured that you are putting the best fish on the table that your family can enjoy. Better and tastier than money can buy.

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