Today’s topic is about dead fish. Dear readers, if you are sensitive or squeamish about the process of killing a fish and what happens then, you may know many situations and conversations in Alaska that you have had to avoid. This article is another discussion of freshly killed fish and what happens after death. It may not be for the faint at heart.
I recently came across an article about fish rigor. Rigor is the state when an animal gets stiff shortly after death. I had never really thought about it before, though I had observed it, and found the topic fascinating.
I would have thought about it as biology as life leaves the fish, but it turns out the process is a chemical one, if you can even make a distinction of the sciences like that.
Though they are two topics, how you treat your fish and what happens when the fish goes into rigor, both influence the quality of the flesh.
When you catch a fish and have decided to keep it and eat it, first you should quickly stun and then bleed it. In an article about how to care for your fish to get the best quality food product, Fish and Wildlife biologist Mark Stopha wrote in June last year that you should stun the fish with one well-placed hit on the head, so that the heart keeps beating.
Then you should, in the case of salmon, pull a gill to bleed the fish. Bleeding the fish properly prevents the flesh from tasting fishy. Stopha recommends doing this in a bucket with cold water, occasionally changing the water. After bleeding his fish for about half an hour, he likes to put it into slush ice to keep it cold, which slows or curbs any bacterial growth that might affect the flesh.
The fish should be kept cold at all times, especially when you fish in the summer; that means getting it on ice ASAP. Remember, bacteria are the enemy and in this case, you don’t see the enemy but you can taste it if they win. Another point made is that one should always handle the fish gently at any stage to avoid bruising of the flesh and pick up fish by the gills to avoid breaking the tissues along the spine.
There are many websites that discuss the best handling of your catch from the water to the table.
What piqued my interest was the process of rigor mortis in fish. Interestingly, rigor mortis may set in shortly after a fish is killed or it may take days before it sets in.
Temperature plays a role in when it happens and how long it takes, and the quality of the meat is influenced by whether you freeze the fish before, during or after rigor. A smaller fish at higher temperature goes into rigor faster. Rigor can also come sooner if the fish is in poor nutritional condition or if it has just expended a lot of energy fighting the line.
When a muscle flexes and relaxes, for example in a swimming fish, there are a number of biochemical processes at work. In the muscle itself, energy is stored to fuel this work.
The use of this energy is a chemical process, and it continues until the supply runs out regardless of whether the heart is still beating or the brain is still sending messages.
Enzymes usually trigger contraction, but also prevent the muscles from going permanently stiff. For some time after death, all these processes keep their functionality; the fish is in pre-rigor state.
This is also the situation in which in your college physiology lab you make the muscle on a dead animal twitch or the reason why a beheaded chicken can still flutter around for a while.
There comes a time when the lack of resupply to these systems causes them to cease functioning properly. Enzymes stop preventing the muscles from freezing up.
In the third stage, post rigor, the muscle relaxes again, and it now has none of the chemical processes functioning anymore. At the same time, the connective tissue that holds together the muscle fibers starts to disintegrate. If this happens, the flesh can become flaky.
If there is too much water in the flesh during freezing, the ice crystals can also cause flakiness. In the industry, this is called “gaping” of the flesh.
I found an article by the Torry Research Station that deals specifically with the problem of when best to freeze your fish with regards to the stage of rigor to prevent gaping.
The article considered the problem primarily in cod, which apparently are prone to becoming flaky.
It seemed that there is no golden rule: If you fillet your fish before it goes through rigor, you risk that your fillets shrink, if the contraction sets in, and now that you cut the skin and skeleton away nothing is keeping the muscle stretched. This may make smaller and tougher fillets. Freezing fish whole before rigor is fine, except if the fish are later thawed to fillet them, rigor can happen during thawing and in that case it also affects texture of the flesh. Freezing the fish after rigor mortis is preferable in this regard, but it can take days for large and well-conditioned fish to go through rigor and they would need to be well dressed and stored cold all the while to prevent bacterial build up. If freezing the whole fish while it is in rigor, it needs to be handled carefully and not forcibly straightened, because that could break the internal muscle structure.
One thing seemed to be consensus in all articles I consulted: You should always handle your fish gently. We should treat the fish we catch with respect, because it is the right thing to do. It turns out, it also improves the quality of our dinner.
Last week, I went out for an evening on the boat. The fog was rolling in and birds were working the feeder fish around buoy four.
A lone humpback whale was slowly moving around us, catching his dinner while we were trying to catch a salmon for ours.
The salmon were not interested in biting except for one relatively small and very beautiful king.
The next day, when I put the tail end into the oven I noticed that it was stiff, in rigor.
I don’t know how baking the fish in rigor affects quality but I certainly enjoyed my piece of fresh fish.
It is an amazing time in this amazing place we live in: Fresh-caught king salmon with fresh Yukon gold potatoes and lettuce both harvested in my garden that day and fresh carrots grown by a friend in Bells Flats. Dinner doesn’t get any fresher or more delicious!