IN February this year the Fishing World website ran Australia’s first survey which examined the behaviour of recreational fishers in relation to how they dispatch the fish they catch.
The survey contained three questions designed to obtain baseline information on angler behaviour; namely if they killed any fish during the course of their fishing trips, and if so, what methods they used to do so. The survey ran for a period of 100 days between February and May 2012.
During this time the survey was completed by 450 respondents. Of these, only eight per cent stated that they were catch-and-release-only exponents who released every fish they caught. While not really surprising, results showing that nine out of ten Aussie anglers keep some fish during the course of their fishing trips are still good to know. Several previous surveys have shown that Aussie anglers release a high proportion of the fish they catch, but this result also indicates that keeping a few fish for a feed remains a prime motivation for the vast majority of Aussie anglers.
The second question was interesting because it found that 55 per cent of respondents had used live bait at some time, while only three per cent of respondents exclusively used dead bait. A total of 29 per cent of respondents only used dead bait or lures during their fishing activities, while 13 per cent of respondents used artificial lures exclusively.
Question number three attempted to determine the methods used by recreational fishers to kill their fish. Respondents were asked to select one of the seven options provided, and in what turned out to be an encouraging result, the majority of respondents (79 per cent) indicated that they used what are recognised as “best practice” methods for killing their catch. Methods such as use of a firm knock on the head (percussive stunning) or decapitation, brain destruction by iki jime or placement in an ice slurry were equally popular, with nine per cent of respondents nominating each of these, while over half of respondents (52 per cent) indicated they used a combination of methods by icing down their catch after it had been killed by stunning, decapitation, bleeding or iki-jime.
Only 13 per cent of respondents indicated they killed their fish by bleeding out alone, while only five per cent indicated that they killed their fish by leaving it to die in air or in a bucket of water.
While there are many ways to kill fish destined for the table, only a few methods maximise the welfare of the fish as well as its eating qualities. The methods that result in a quick death (such as a knock to the head or iki jime) are by far the most preferred, not only from a fish welfare perspective, but also because they reduce undesirable changes to the fish flesh. Such changes include increased lactic acid buildup and early onset of rigor mortis (the contraction of muscle fibres after death), both of which reduce the eating quality of the flesh.
Blood contains various enzymes which degrade flesh after death and also nutrients which allow bacteria to flourish within the blood vessels. Bleeding fish therefore reduces the initial rate of bacterial spoilage, improving fillet quality. However, bleeding out by itself is not considered to be a humane method of killing. Because of this, fish should only be bled after they have been stunned or killed using another method such as brain spiking or percussive stunning. In general, the faster the fish can be killed, bled and its flesh iced down before the onset of rigor mortis, the better its quality and the longer its shelflife.
In contrast, slow killing methods such as bleeding fish out at ambient temperature without stunning first, or leaving fish to flap about and die slowly on the ground or in a bucket of water, are highly stressful. This stress results in higher levels of lactic acid build up and other changes that significantly reduce the quality and shelf life of the fish’s flesh. Because of this, it was encouraging to see that asphyxiation in air or a bucket of water was the least popular method used by the survey respondents. However, the fact that some people are still using these methods for killing their fish was disappointing, showing that we still have work to do educating anglers regarding what is best both for the welfare of the fish they catch, as well as the eating quality of their feed of fish at the end of the day.
The survey indicated that around 61 per cent of respondents used ice as part of their dispatch routine. This was an encouraging result, given that keeping fish cool reduces spoilage caused by proliferation of bacteria after death. The high-risk temperature zone for bacterial growth is between 5° C and 70° C, and under most fishing scenarios use of an ice slurry at 0-2° C is the best way to get the core temperature of the fish down below 5° C as soon as possible after death.
Ice slurries can be made by mixing ice with water obtained from the fishing spot at a ratio of at least one part ice to one part water. Ratios of two or more parts ice to one part water in a decent insulated esky will ensure that your ice slurry remains effective for several hours, even on the hottest days. Remember, that if ice is used in large lumps instead of a slurry, cooling times are significantly longer due to the reduced contact between fish and ice and the insulating effect of air spaces in the mix. A mixture of ice and water is guaranteed to maximise the surface area available for cooling, but make sure you monitor the mix and add more ice when required as it melts.
Over half of the survey respondents (52 per cent) indicated they used ice in combination with other methods (e.g. bleeding, stunning/decapitation, or iki jime). This is logical because unless fish are to be eaten immediately, optimal results will always be achieved only with a combination of an appropriate killing method followed by bleeding the fish while on ice. Use of the ice slurry alone as a killing method is controversial, given that larger fishes and cold adapted fish species (e.g. trout and other salmonids) are not normally stunned by placement in an ice slurry. Because of this, they may retain brain function for some time until hypothermia and/or asphyxiation occurs.
Nevertheless, scientific studies suggest that the process of inducing hypothermia via ice slurry is not necessarily overtly stressful to cold adapted species. Also, even though large and/or cold adapted fish may take a relatively long time to die in an ice slurry, for smaller fish less than approximately 500 grams and most warm water species (including some Australian species including bony bream, whiting and garfish), thermal shock due to exposure to a water temperature differential of around 20° C greatly shortens the time to loss of brain function and death. Because of this, while killing your fish first before placing it in the ice slurry is always preferred, use of ice slurry alone can still be justified under Australian conditions, at least under certain circumstances.
Of all the methods available to kill fish, a firm knock to the head (percussive stunning) or brain spiking (iki-jime) remain the most humane, as both can result in instantaneous death when properly administered. Because a firm knock on the head requires little skill, it is the preferred killing method most often recommended for recreationally caught fish, provided it is done swiftly and delivered to the correct location (the area just above the eyes). In contrast, iki-jime (a Japanese term denoting “live killing, or to terminate while alive”) is a method used to destroy the brain using iki jime spikes that can now be obtained in many tackle stores. A sharpened screwdriver or sharp knife are other equally effective, zero cost tools. Administered accurately, iki jime can be the fastest, one-step process which results in the lowest levels of stress and highest quality fish product compared to all other methods of dispatch. Once you spike the brain it is destroyed and the fish is immediately killed, drastically reducing stress, lactic acidosis, bruising from thrashing around and other undesirable changes which occur if the fish is left to die slowly in air, in a bucket, or even in an ice slurry. For more details on how to iki jime your fish, keep an eye out for the free pamphlets in the September edition of Fishing World magazine. Also check out our “how to” video HERE which demonstrates the iki jime method.
Tools that can be effectively used for employing the iki jime technique.
Putting it all together
To summarise the topic of humane killing, let’s go through the process I use for fish I catch for my own family’s personal consumption. Once a fish is chosen for a feed I kill most species immediately by iki jime. Having said that, dangerous toothy critters such as mackerel and wahoo, or boat wreckers such as cobia or dolphin fish are stunned first with a blow to the head with a “priest” or club in the interests of safety. Whiting can also be dispatched quickly by turning them upside down, grabbing the head and pulling it upwards and backwards towards the tail, which will kill them immediately by breaking their neck. But for all other species, brain spiking is the fastest and most humane method of dispatch.
To assist you to locate the correct area to destroy the brain in several popular target species, check out the neat “how to” iki jime pamphlets in the September edition of Fisho.
After humanely killing your fish, it is desirable to bleed it to improve flesh quality even further. For most fish the easiest way to bleed them is to sever the arteries in the isthmus (or throat) of the fish after it exits the heart and before it enters the gills. After bleeding, get the fish into an ice slurry as soon as possible. Try it. You’ll be rewarded for your efforts with delicious meals for you and your family of the best quality fish that money simply can’t buy.
Dos and don’ts of fish dispatch and storage
- Kill your fish immediately using iki jime or a firm knock to the head, then bleed and ice.
- Use at least 2 parts freshwater ice to 1 part seawater in a seawater ice slurry
- Remove the gills and guts when you can, taking care to avoid contamination of the flesh.
- Keep fish on ice or in the fridge if you want to eat it in the first 24 hours after capture.
- Leave your fish to die slowly in an ice slurry or worse, by asphyxiation in air.
- Scrub the gut cavity to remove membranes that protect muscle from bacterial invasion, (for small fish leave scaling until after the fish is chilled).
- Use ice made from seawater to chill fish in a seawater slurry – the resulting temperature is too low and begins to freeze the fish slowly.
- Leave your fish in an ice slurry for longer than around 12 hours. If longer term storage is required, re-ice onto normal ice or freeze as fast as possible to avoid ice crystal formation, but only after rigor mortis occurs.