Ike jime takes some practice. Ike jime has its detractors. But ike jime is not a magic trick; rather ike jime is equal parts science and equal parts skill. This method creates certain “windows of time” for the handler to exploit, and this beginner’s guide will explain why and when these windows appear.
Equipment for Traditional Ike Jime
To begin, the handler will need tools and equipment that are appropriate for the size, species, and context of the fish at issue. As a general matter, here is a list of the most basic equipment:
- A sharp brain spike;
- A sharp knife;
- A source of clean water;
- An insulated cooler filled with ice, and
- A live fish.
Ike Jime Brain Spike (the noun)
The handler will need a spike that can easily puncture a fish’s skull and destroy the fish’s brain. What kind of spike? It depends. Even a tiny spike plunged into the hindbrain of large tuna will kill that fish instantaneously. But size matters too. A tiny spike may not have the necessary strength to puncture the skull of a large tuna easily and quickly. Perforating a fish’s head without killing it may introduce new challenges, and broken spikes are not particularly safe or effective. It helps to select an application-specific brain spike made of stainless steel, sized appropriately.
Ike Jime Brain Spike (the verb)
A fish can only breathe underwater. Once the fish is removed from water, its ability to breathe stops. Just as land-based animals may temporarily hold their breath when submerged underwater, fish are able to do the same – temporarily. This is the first, critical WINDOW OF TIME to immediately kill the fish and limit its ability to experience any stress. How?
A brain spike is one traditional (manual) method. It is simple, efficient, and effective when performed properly.
Locate the brain of the fish. If it is helpful, study a fish’s head carefully beforehand so you are prepared to hit the brain on the first try. Alternatively, here is a great resource by Dr. Ben Diggles. While this compendium focuses mostly on species available in and around Australia, a pattern emerges: the brain is almost always located 1) at the top of the pre-opercular line, and 2) where that point will intersect with the fish’s midline.
With some limitations on species, size, and circumstance, the brain spike may enter the brain from any angle. Some prefer to enter from one side of the fish’s head. Others prefer to enter from the front of the fish’s head. Again, species, size, and circumstance matters. Pro Tip: regardless of the direction, try to angle the spike towards the top of the spine.
Finally, obtain a live, energetic fish. A fish that has been floating belly-up on a stringer will not be redeemed, nor will a fish that has been entirely exhausted after a long, drawn out fight off-shore. The fish should be robust and as full of its natural energy as possible.
Step One in the Ike Jime Method
The handler must control a slippery fish that will almost certainly jerk and thrash during this stage. Methods of control include restraining the fish against a solid flat surface or grasping the fish by the lower jaw or gill cover. Plunge the spike firmly into the fish’s skull, endeavoring to reach the top of the spinal vertebrae that run in along the mid-line of the fish. The spike need not travel so far as to impale the fish entirely — just far enough to travel through the brain. Performed correctly, the fish’s entire body will immediately seize, its mouth, gills, and dorsal fins will flare, and the fish’s body and tail may begin to spasm. Stay calm and maintain control of the fish. The spasms will pass.
At this point, the fish is brain-dead and can no longer experience the stress of suffocation. Stress causes a fish to release natural compounds like cortisol, adrenaline, and lactic acid. These compounds impart off-flavors and smells into the muscle tissue and also get worse over time. However, if a fish does not suffocate, it does not stress; if the fish does not stress, these compounds are not released. The brain spike can control the biochemical consequences of death.
Step Two in the Ike Jime Method: Bleed the Fish (Exsanguination)
The lion’s share of a fish’s bacterial load exists in the blood and gut cavity of a fish. Ridding the carcass of this bacterial load is essential, and draining the fish of as much blood as possible is relatively simple.
Certain involuntary muscle movements will continue to function for a short while in a freshly-killed fish, and in particular, the heart. The fish’s heart will briefly continue to beat and supply residual blood pressure through its circulatory system. This is the second WINDOW OF TIME to ensure your catch remains as pristine as possible.
Lift the gill cover with one hand and expose the gill arches. Insert a sharp knife and follow the circular curve of the gill cover and cut through the thin membrane that connects the gills to the collar. Alternatively, cut in a perpendicular line through the gill arches. Even another method involves cutting the isthmus (or throatlatch) of the fish, which is the tapering point on the underside of the fish that connects the head to the body. In short, bleeding a fish by rupturing the gills is not particularly difficult, and the fish will bleed easily.
Passive bleeding like this should also include a tail cut. A major artery runs along the underside of the spinal vertebrae of the fish. Sever it. But to do so, it may be necessary to remove a few scales before making a firm cut through the spine as well. In order to cut through the spine, slice quickly through the flesh until you feel the spine, and press down hard while taking care not to sever the tail entirely. Then, fold the still-connected tail back to expose the artery (and the spinal vertebrae, and the neural canal).
Fish blood coagulates quickly, and there’s more than you might think. Submerge the entire fish into clean, ambient-temperature water to help the blood drain out more easily. Holding the fish by its throat and shaking it vigorously in the water for a few seconds is highly effective. For some species, folding the fish gently into a “C” shape and applying pressure to squeeze out residual blood is also highly effective. Leave the fish to continue bleeding out slowly for no less than ten minutes. For pelagics and certain other large species, hold a wash-down hose beneath the gill plate and try to flush out as much blood as possible.
Step Three in the Ike Jime Method: Rapid Cooling
Cold temperatures limit bacterial proliferation, but cooling must be comprehensive. Simply tossing the fish into a bucket of ice is insufficient to comprehensively cool the entire fish, let alone evenly. A fish laying atop a bed of ice on one side only will not cool on its other side at the same rate.
Instead, create an ice “slurry.” A slurry is a 1:1 ratio of ice to water. This allows the fish to enter rapidly into the cooling process, which will slow the rate of bacterial proliferation dramatically. Ideally, pack fish “soldier style” (i.e., alternating nose to tail in rows), with their bodies positioned in a straight line. This packing style is the precursor for one of the most important natural processes that boosts the flavor and intensity of your catch — rigor mortis.