I copied this information off of another site a while back.. it is a very long read but some awesome information on how to care for tuna. So here it is
As promised from the head/tail king thread here's the fish care/cleaning/storage thread. This will be lengthy so I'll break it into a couple or three posts. Probably the first things to consider are your personal tastes and styles. I think this diagnostic test will be a pretty reliable tool to help you decide whether to keep reading or move on to something else. If you go to the grocery cooler and look for the cheapest beer they have, then this will be a waste of time for you. On the other hand, if you're more likely to follow the Warsteiner slogan, "Life's too short to drink cheap beer," then all the Japanese style production will make a big difference to you. To be honest, the number of fish we have on the table goes a long way in determing whether I use traditional Texas slash and bag, do the full Japanese treatment or something in between. It just takes a lot longer Asian style. So you have some idea where all this blather is coming from, I acquired this information (it's wonderful party trivia!) from a combination of being an obsessive/compulsive fisherman like you guys for over 40 years, chasing advanced degrees in marine oriented science to a dissertation short of a Ph.D and about three years of informal apprenticeship under a master sushi chef. We traded, I taught him fishing and he tried to teach me the sushi biz.
For a sushi chef, thinking about dinner starts before the fish is hooked. Prepare your coffin with the smallest cubes available or even better, blown snow style ice. If you have larger cubes then it is best to make a saltwater slush by adding enough seawater (do this offshore, not in the harbor) so that it is easy to slide your fish in and submerge them as they are caught. I have read where some guys add rock salt to the mix to super cool it like we did on kegs in college, but when I tried that I ended up with frozen fish. The extra high salinity cools the water below the freezing point of the fish and that isn't what you want. The next consideration is using tackle that will bring the fish in as quickly as possible. Fish biochemistry differs from humans considerably, but they undergo anaerobic respiration in their muscles when in "fight or flight" mode just like we do. That means that the longer they are on the string, the more lactic acid buildup you get with a proportional loss in food quality. It's like the poorly shot deer that has strong tough venison, well similar anyway. OK, so we got the AJ at the boat. It's decision time. Do you really want to sink that gaff into the loin where it will hold, or into the belly where you won't lose loin but it might rip out? The sushi chef doesn't like either alternative. On an AJ (and most other fish) the loin above the backbone is the meat and potatoes part of the fish but the belly is like caviar and escargot all rolled into one, especially in tuna (you see it as toro at the sushi bar, the most expensive cut of tuna). So, you take your time and stick him under the throat latch (a bad idea on sharks, they tend to want to swim right up into the boat when you do that, jaws snapping). Open the coffin and swing the fish into the box in one motion. No posing for photos yet. The fish won't like the ice one bit as you know, but the slush will give and not provide him anything to bang against, which reduces bruising tremendously. It has the same benefit on the ride home if you're pounding into a chop. The slush also makes contact with the fish over 100% of its body and thus chills him a whole lot faster than cubes with air spaces between. As soon as you think the fish has chilled enough to be calm, but not dead, take him out and bleed him by cutting that throat latch right where it widens into the body. The fishes' heart lies right behind that cut and the biggest artery in the fish runs between the heart and gills so this will empty him fast if his heart is still beating. You'll conserve ice if you can bleed him out of the ice chest (I have a bait well by the box that drains out of the boat and it works great for this), but if you bleed him into the box it isn't critical. All fish benefit from this by the way, not just tuna, mackerel and sharks. It's more important on scombrids and sharks for various reasons. It's needed on tuna and billfish because they maintain their body temperature higher than their surroundings so bleeding removes heat fast, on mackerel because they are very bloody and will taste strong if you don't bleed them and on sharks because they carry urea in their blood to help balance that osmosis problem and it breaks down into really nasty ammonia-like compounds right after death. After you are satisfied that he is bled out gut him, but don't cut through the throat to the gills on bottom fish. That part is too valuable on snapper, grouper AJ's etc (more on that later). It's not such a big deal on pelagics. Once you have all this done slide the fish back into the slush so that the body is in a verticle swimming position with its head down like it is swimming for the bottom of the coffin. This allows any other loose body fluids to run out of the fish at your cuts instead of pooling in the meat and it helps to further reduce bruising on the way home. If you were really lucky and the fish was a beast that won't fit in the box, cut off the tail before the head. The tail meat is the least desireable on the fish. You'll notice that when you go on charters out of the country and ask for some fish to take to a restaurant or whatever, the mate will almost always give you the meat from behind the dorsal fin to the tail unless you specify otherwise. Those guys know what they're doing and they're gonna keep the best for themselves or to sell at a higher price. If you still have to remove the head (lucky you) then make double sure that you have either made a salt water slush or if you had crushed ice that the coffin is drain open for the rest of the trip. The meat above the backbone up by the head is the best block of meat on the fish (there are arguments on this between belly and loin men). It's not anatomically the same as the tenderloins on a deer but qualitatively they are analogous so you don't want it screwed up from freshwater ice melt. Freshwater contact can mess up your fish faster than anything else if you're not careful. Fish skin acts as a natural barrier to the evils of osmosis so as long as it is there you're OK. Expose the meat to that freshwater unprotected and within seconds freshwater runs into the cells and explodes them like overfilled water balloons. There goes your tasty fish, and how much did it cost per pound? OH MY! If you make a slush that has a similar salinity level to fish fluids, then the the power to the osmosis engine is cut off and your fish is safe. If a little melt dribbles over the fish on the way to the bottom and out the drain it's way better than having your fine cuisine soaking in it for hours. So that's what you would do with fish number one. Now repeat that process several more times until the box is full and head for the house. Next installment will be the saga of the cleaning table.
I'm glad you guys found the information interesting and I'll see if I can't make this one more reader friendly for speckle-catcher . Oh yeah, wishin4fishin, you're right. That's a bad idea and I'll cover it in the next installment.
It has been a long hot day of fishing and you're finally back at the dock with a box of fish. Now you can drain all the saltwater out of the box so you won't get a hernia lifting it out. We'll assume a perfect world here and you are able to get your fish to the table easily and there isn't anybody else anywhere around. As you approach the table a half dozen sleepy seagulls that have been roosting on the table take wing, each of them depositing a nice oyster sized glob of processed gull food right where you'll be cleaning you catch. There are gulls even in a perfect world. There are tap water hoses for you to rinse you catch and several lengths of 2X8 lumber to use as cutting boards.
Obviously, if you are thinking about eating your fish raw there are some things here that are unacceptable. The provided cutting boards have been in use for who knows how long and cleaned up with a minimum of care, if at all, for as long as they have been in use. The gulls have probably never left a deposit on them either, right? The point is, the cleaning table should only be used for the preliminary cleaning that you really don't want to do at home.
Step one is to decide how the fish will end up. Most of the time we don't even consider options other than fillets, but in the world of haute cuisine this is the least desireable form. Fish cleaned with skin and bone intact hold better, freeze better, give you more options later and if you cook them, they yield a much moister tastier product than boneless skinless fillets. Optimally all you do at the cleaning table is gut the fish if you didn't do it at sea, scale and rinse them. Even here you can make a difference though. Just take the fish out of the box and work on them one at a time and then put them back in the ice. You went to the trouble and expense of all that ice to keep your fish cold so don't waste it by piling the fish on the table to get hot while you work. You'll get some funny looks for scaling your fish, but it's a little like having numbers to a spot that nobody else has. Just smile and keep working. That's all you want to do here. Everything else occurs in a way more sanitary environment, like your kitchen.
The good news is that your fish are now in a kind of suspended animation in terms of quality and as long as you keep them vertically on drained ice, they will actually improve for three days. So, you can get all the rest of the chores done and rest up some before you become a bona fide fish butcher. I probably ought to explain that 'improve for three days' thing. The old saw, "Fish are best right out of the water", is a myth. Fish is protein just like lamb, beef, pork or venison and all those proteins benefit from aging as we all know. So why not fish? The molecular structure of fish protein is slightly different from mammals, but it still improves with proper handling. The fish need to be kept on ice, not in the refrigerator, and held in that same vertical position to allow draining. Tip the ice chest so that it drains most efficiently and add ice to keep the fish covered as necessary. Like this, fish improve to the end of the third day after capture and then hold there for 24 hours before beginning to decline in quality. If I haven't eaten the fish by the fifth day, they get frozen. This is an average for all fish. The process is slightly faster for dolphin and slower for snapper. Tuna are the benchmark for this system. Tuna sashimi right on the boat is good if you eat it still "dancing" with life, but if you wait until the fish is stiff before slicing, it will be the toughest sashimi you ever eat.
OK, that takes care of the cleaning table. Essentially, just use it for rough cleaning and then get out of Dodge. I'll tackle the kitchen angle next time.
One the reasons I spend way more time on this board than I probably should is that I continually get to learn new stuff. There's a scientific theory (I forget the name) for coming up with new things after you have spent some time looking. You know how the learning curve is really steep whenever you first start something new like fishing offshore or learning a piece of software (I hate it when that happens) and then after a while more and more time passes between learning new things. That hasn't happened to me on this board. Everytime a thread opens up I'm learning something about rigging or outboards or oil rigs and this time I'm even learning things about something that I have researched enough to publish 3 magazine articles on. Thanks.
Regarding ice versus the refrigerator: Ice stays the same temperature, refrigerators do not. It might be a picky difference but remember that this is one of those Japanese precision things. Ice is just better. And then there's the plastic bags touching the fish thing. That is supposed to cause a problem due to lack of oxygen exchange, but I don't have any data to support it. Sushi chefs usually wrap their fish in paper and then plastic over that if necessary.
Regarding the bacteria breakdown aging thing: I wondered about that too but I never looked it up until now. The bacteria is only involved in creating the crust on the outside of dry aged meat. The tenderizing comes from enzymatic action on the actin/myosin complex muscle fibers (proteins breaking down other proteins). I couldn't find scientific studies on how this works with fish. Something for me to work on when I get the time. You guys will need to donate wahoo steaks (bone in of course) for my research to further the scientific benefit to mankind! Anyway I bet the same thing is going on there and it is enzymatic "relaxation" that makes tuna so buttery after 3 days on ice.
Regarding the toro vs the other parts: Technically it is otoro (an o in front of a word in Japanese indicates that it is the genuine, real deal), the loin is referred to as chutoro and the blood line is ami, which simply means red meat. Accessing the toro is relatively simple and I explain it below in the kitchen part of this post.
Regarding the pithing process: You guys totally got me on that one, I had never heard of it so I did a little snooping on a science/fishing board. I clipped the most revealing post and it follows in italics. I'm going to have to try it. To help with the science jargon for you guys who took biology too long ago, glycogen is the substance that is formed when an organism takes in more calories than it burns. It's like a fat precursor and its abundance elevates the quality of the meat. Interestingly, you'll notice that the majority of Mr. Howgate's references have Japanese authors.
Beginning of post........In the discussion of this topic it is necessary to differentiate 'pithing'
and 'spiking'. Spiking, described in Ken's message, is the process of
destroying the brain by passing a spike through the skull into the brain.
Pithing goes further than this and is the process of inserting a wire into
the spinal column of the fish to destroy the spinal cord either through the
skull after spiking or from a deep cut through the vertebral column behind
the head, described in the original message from Richard Lord. Spiking
renders the fish unconscious so that it does not struggle and a similar
effect is caused by giving the fish a hard blow to the head, a method of
stunning farmed salmon on harvesting. Though the fish is rendered
irreversibly unconscious by spiking of by stunning, all muscle activity
not cease. The muscle at least twitches, if not occasionally flaps. Pithing
stops all muscle activity. The various methods of killing fish, or letting
fish die, affects the time taken for the fish to enter rigor mortis, and to
some extent the time in rigor. I shall not try to summarise the
of the rigor process and the way the killing methods affects the
biochemistry, but pithing does maintain glycogen levels in the muscle as
Richard recalls. It should be noted that when different methods of
slaughtering fish are compared, all of the glycogen is ultimately converted
to lactic and the post rigor pHs of the flesh are the same; what is
different between the killing methods is the time course of the glycogen
depletion and lactic acid formation.
Delaying the onset of rigor is important for some uses, for example, for
sushi products, and there is an advantage in pithing fish. For other
outlets, for example, production of fillets, there is no advantage, and
disadvantages, in delaying onset of rigor. Where the effects of killing
methods on subsequent spoilage have been studied, there has been no effect
of killing method on storage life.
I had not come across the effect of spiking in reducing the time to cool
down described by Ken Hildebrand. I wonder if it the result of inhibiting
twitching of muscle and the consequent heat generation, or is there some
other effect on the biochemistry of the fish.
I am intrigued by Peralta's message. How do you pith a cuttlefish, and what
aspect of quality is preserved?
Amano, K., Bito, M. & Kawabata, T., 1953, Handling effects upon biochemical
change in the fish muscle immediately after catch I. Difference in
glycolysis in the frigate mackerel killed by various methods. Bulletin of
the Japanese Society of Scientific Fisheries, 19, 487-498.
Ando, M., Banno, A., Haitani, M., Hirai, H., Nakagawa, T. & Makinodan, Y.,
1996, Influence on post-mortem rigor in fish body and muscular ATP
consumption by the destruction of spinal cord in several fishes. Fisheries
Science, 62, 796-799.
Azam, K., Mackie, I.M. & Smith, J., 1989, The effect of slaughter method on
the quality of rainbow trout (Salmo gairdneri) during storage in ice.
International Journal of Food Science and Technology, 24, 69-79.
Boyd, N.S., Wilson, N.D., Jerrett, A.R. & Hall, B.I , 1984, Effects of
destruction on post harvest muscle metabolism in the fish kahawai (Arripis
trutta). Journal of Food Science, 49, 177-179.
Iwamoto, M., Yamanaka, H., Abe, H., Ushio, H., Watabe, S. & Hashimoto, K.,
1988, ATP and creatine phosphate breakdown in spiked plaice muscle during
storage, and activities of some enzymes involved. Journal of Food Science,
Jerrett, A.R. & Holland, A.J., 1998, Rigor tension development in excised
"rested", "partially exercised" and "exhausted" chinook salmon white
Journal of Food Science, 63, 48-52.
Mochizuki, S. & Sato, A., 1996, Effects of various killing procedures on
post-mortem changes in the muscle of chub mackerel and round scad. Nippon
Suisan Gakkaishi, 62, 453-457.
Nakayama, T., Matsuhisa, M., Yamaura, M., Sumiyoshiyama, T. & Ooi, A.,
Delayed example in rigor mortis of spinal cord destroyed plaice detected by
measurements of isotonic contraction and isometric tension. Fisheries
Science, 63, 830-834.
Nakayama, T., Toyoda, T. & Ooi, A., 1996, Delay in rigor mortis of red
sea-bream by spinal cord destruction. Fisheries Science, 62, 478-479.
Enough old business, it's time we got to the kitchen.
The fish come out of the ice one at a time and get rinsed in tap water for the last time. Now they are thoroughly dried with paper towels. You'll be amazed at the difference in cutting up dry fish vs wet. Done right, you will not even feel the slightest urge to wash the meat. It will be cleaner than any you've done before. If you don't get the fish dry and you get a little goop on your fish, mix up some salt water (about a tablespoon per quart) with plain salt and bottled (not tap) water and you can wash them without the burst cells problem. Anyway, the first item is to remove the head, but sushi chefs take off a lot less than we normally do. The cut runs from the top of the head down in front of the rear gill collar down to the throat latch that you already cut when you bled the fish on the boat. Now is the time to remove those cheek scallops from the head that are so popular and then discard the rest of the head. Next it is time to remove the belly pieces and throat. After you have done this a few times this step is pretty simple with just a knife, but the first few times through you'll be happier if you have some heavy duty kitchen/game shears or tin snips for snapping the gill collar at the backbone. Start cutting the belly back by the vent and work forward along the bottom of the backbone, through the ribs until you run into the juncture of the backbone and gill collar. This is easy with a serrated knife. There really is a little seam there that allows you to complete the cut with your knife, but like I said it usually takes a few practice runs before you are comfortable with it. So, get out your shears and snap it off next to the backbone. Now repeat this on the opposite side. You'll end up with a giant butterfly looking piece of meat and just how giant the butterfly is determines your next move. Just keeper snapper, small grouper, redfish and the like can keep this whole. All you do is make a cut on the inside of the throat on the midline so that the butterfly wings lay flat. This meat will have bones, most of them large and easy to get around but you'll have to warn the family members used to fillets. The reward is outstanding fish and that is not overstating the claim. These areas of the fish do the least work but store the most fat. Just like a well marbled prime rib this is really good stuff grilled, fried or broiled (on bottomfish, mahi and wahoo. For most AJ's split the collar into 2 halves, they're too big to handle as one piece. This section is the Gulf equivalent to a Japanese classic done with their 8 to 12 pound yellowtail (same genus, different species from AJ's) called the hamachi kama. Hamachi is yellowtail and the kama is the collar section with a little of the front part of the belly attached. Just don't toss the kama word around too loosely without a fish name in front of it. By itself, kama is Japanese slang for gay, so in the wrong crowd you might make a sumo wrestler pretty unhappy with you! The rear part of the belly on yellowtail, or AJ's is reserved for high quality sashimi.
OK, now we've got the carcass trimmed down to the basics and the rest is pretty much what you have always done. The sushi chef has a ritual of slicing the length of the fish just under the skin along the dorsal fin on one side then along the anal fin and then along the anal fin on the other side and finally the opposite side of the dorsal. There's a name for that technique, but it has flown out of my brain for the moment. They then retrace their steps completing the cuts down to the backbone and finally removing the fillets where they attach to the backbone by pretty much just lifting them off. On small fish like flounder and just keeper trout the backbone is broken in half and then marinated in a combination of soy and sake and then deep fried for an appetizer. Sounds weird but I have had guests turn down entrees for more "fried bones!" Larger fish have the remaining flesh removed with a teaspoon and this is mixed with minced scallion and some nanami togarashi (Japanese 5 spice) or other ingredients and used as a filler for makizushi (rolled sushi). There's not much left for the garbage guys to haul off.
Tuna are more involved due to their roundness, but it's not that big of a deal. Make an additional cut the length of the fish down its lateral line so you end up with 4 loins instead of 2 fillets. Remove the blood line (your cat will love you) and you are good to go. If you plan to work on sushi and sashimi for several days on a large fish, only cut off the carcass what you need for that session. Cover your fish in parchment paper and then plastic wrap and return it to the ice and you're good to go the next day.
As for freezer storage, you can't beat vacuum sealers. I use a Foodsaver Pro that I've had for over 15 years and the darn thing is still going strong, hope I didn't just jinx it! I have grilled year old blackfin stored that way next to month old blackfin and been unable to tell the difference, they're that good.
I think I hit just about all the basics, but if you guys find any holes or have questions I'll see if I can't get to em in a few days. But I'm not going to be in a hurry with 42020 forcasting Instigator level seas for the weekend. See you guys out there.