Looking After TunaAlthough the most recent Yellowfin Tuna seasons in New Zealand waters have been nothing to write home about, many of us still look forward with anticipation to what the up-coming summer months hold. We have all been really excited about what’s going on with the winter Bluefin fishery on the South Islands west coast, but it’s the traditional summer yellowfin grounds in New Zealand (such as the eastern Bay of Plenty and Whitianga) that provide most of us with our annual tuna fix. As long as it is cared for and cooked properly, Yellowfin tuna is my favourite eating fish, bar none. Tuna offers a huge variety of eating options and it is suitable for a number of tasty dishes. I realise it is always a trade-off between having a nice tuna weighed at your local fishing club or preparing it for eating, but it never ceases to frustrate me when we see tuna at weigh stations around New Zealand that have spent all day uncared for or unchilled in the cock-pits of boats. I’ve heard Chinese whispers about some tuna that get dumped or minced up as berley bait and although the thought of it frustrates me no end, I guess that’s about all the flesh is good for in a lot of cases. All table fish requires care in preparation, but none more so than the tuna species. It’s no secret that all tuna have extremely delicate flesh. How tuna is caught, killed, bled, gilled and gutted, chilled, processed, stored, and cooked (or uncooked in a lot of cases) all have a major effect on its final eating qualities. The following are a few pointers I picked up from some of my Australian, Japanese and Hawaiian friends on how to prepare your tuna and a couple of dishes that you might like to try rather than sending it off to your local smoker, using it as berley bait or simply wasting it. Hopefully it will help out this summer and many of you can enjoy the wide variety of eating that tuna provides. As with a lot of fish, using an ‘iki jimi’ (spike to the brain) is the quickest, most humane and effective method to kill your tuna. I realise a lot of fishermen simply give the tuna a good clout on the top of the head with a fish bat, and that too is effective for obvious reasons. But the reason an ‘iki’ spike is preferred is because it kills the fish instantly, stopping most of the nerve activity throughout the tuna’s body. A lot of times when a tuna is hit on the head with a fish bat, the fish will go into a full body spasm as all the fast twitch fibres shake uncontrollably. This releases large amounts of lactic acid into the muscles and flesh around the tuna’s core. Flesh is also damaged due a rapidly elevated body temperature but we will talk about this a bit more later on.
All tuna have a small pale whitish spot situated on the top of the head and between the eyes; this is where the brain is situated. The iki spike is inserted here at approximately a 45-degree angle back towards the fish’s ventral fins. With one firm and accurate push, the tuna should be killed instantly and stops the majority of the body’s nerve activity.In a lot of cases, some of the muscle fibres along the tuna’s spine still twitch unseen from the outside, and have an adverse effect on the flesh’s eating quality. To kill off all the remaining nerve activity a length of monofilament or wire needs to be passed along the core of the tuna’s spine. I generally use 200lb-400lb monofilament as it’s firm enough and the right diameter, with a bit of gentle persuasion it should pass down through the brain, all along the inside of the fish’s spine to the tail. I’m sure professional tuna fisherman and surface long liners have better ideas, but from a recreational standpoint 200lb mono is more than adequate. Bleeding improves the appearance of uncooked tuna flesh, helps initially to reduce the fish’s body temperature and also gets rid of all the bacteria located in the fish’s blood stream that may foul the flesh. All tuna should be bled for 10 to 15 minutes after iki-spiking and then immediately chilled. This is most effective when done immediately after the fish is landed, and when the heart is left intact, taking advantage of its pumping action. There are at least three ways to successfully bleed a tuna. If one cut does not produce blood, try one of the other methods. I usually try more than one cut to promote more efficient bleeding. The pectoral cut is generally the best form of bleeding tuna. With the fish on its side, measure about the width of two fingers from the base of the pectoral fin along the lateral line. Make a shallow cut through the lateral line using a clean, sharp knife. If this cut is made too deep or too wide, usable flesh can be damaged so only a small knife is required. Flip the fish over and repeat the cut on the other side. Cutting the gill arch is another common and effective method used. With the fish on its side, lift the gill cover and sever the gill arch by inserting the knife behind the gill through the gill membrane, and cut up toward the spine, severing the blood vessels at the top of the gills, while still leaving the throat latch in tact.
I usually make a small cut across the lateral line down by the tail, although this generally doesn’t release a great deal of blood, it just gets rid of any blood that can’t be drawn back to the pectoral cut or gill area.Once your tuna has been successfully ‘iki’ spiked and bled, it should be gilled and gutted or dressed ready for chilling. Make a cut all the way around the gill membrane, cutting all the gill attachments to the head. Then make a cut around the anal opening. By only cutting around the anal opening and leaving the belly in tact, this prevents the flesh from spoiling when iced or placed in a slurry or brine. From here the gills and gut can be removed through the gill cover in one piece. I usually give the gut cavity a good wash out with seawater just to remove all the blood, loose tissue and remaining gill membranes as they can harbour any bacteria that may spoil the flesh. Chilling your tuna is probably the most important aspect when maintaining good eating qualities. With a large amount of New Zealand’s tuna fishing done from trailer boats, I realise that this is not always easily achieved. There are a number of very effective and affordable fish bags available on the market today and a fish bag and a couple of sacks of salt ice are worthwhile investments for any fishing expedition. If you do choose to use salt ice and a fish bag, a good suggestion is to pack the gut cavity with as much ice as you can. This cools the inner core of the tuna as quickly as possible. As we all know, the tuna species are extremely warm-blooded in comparison to other fish and require a lot of cooling to prevent spoilage. I like to use a slurry or brine bin and leave the tuna in there for up to 24 hours, but I realise not everyone has that luxury on their boats. All I can say is that the flesh is absolutely outstanding if you can chill it down as quickly as possible and keep it chilled for as long as possible without freezing it.
We all have our own filleting methods so I guess I won’t go into to much detail here other than to say that care does need to be taken to ensure that wastage is keep to a minimum. As with many fish, filleting a well-chilled tuna is generally much easier than filleting one that has been sitting on the deck all day. I usually remove the fillets and then quarter each fillet by removing all the remaining bloodline and pin bones. Rib bones are also removed from the area around the gut cavity. From here I simply take a suitable skinning knife and remove the skin from the loins.I generally prefer to not wash the flesh much at all, even with salt water. I prefer to wipe the flesh with either paper towels or newspaper and store them dried and wrapped in kitchen wrap and place back in the refrigerator ready for eating. I find if tuna is stored wet, it will sit there stewing in its own juices and by the time you try to eat it, it has a horrible mushy composition and generally doesn’t taste that great. If it’s refrigerated dry it will become very firm and have a fantastic colour and texture. I find the flavour actually improves with ageing in the refrigerator, similar to red meats. If you choose to freeze some of your tuna, all I can suggest is that you freeze the loins individually in sealed airtight (vacuum packed) bags free from any water or juices that can spoil the flesh…no secrets there! We all know about the popular Japanese style of thinly sliced raw fish called ‘sashimi’ which is usually accompanied with soy sauce, wasabi and pickled ginger. I realise it’s quite difficult eat all of your typical New Zealand Yellowfin as ‘sashimi’ and most us would have certainly over eaten if we had all our South Island Bluefin as raw fish (not to mention visiting the toilet on a regular basis!). Here are some other options that you may like to try in the future. Another tasty ‘sashimi’ dish I like to do is searing a tuna loin in a Cajun and breadcrumb mix. I generally use a little bit of egg just to bind the breadcrumb mix to the fish and sear the outside of the flesh only for about 5-10 seconds on each of the sides. I like to chill the seared loin down again in the refrigerator, once chilled, slice it thinly across the grain for eating. You may like to get a little adventurous with the breadcrumb mix with ingredients like sesame seeds, pepper, Parmesan cheese, chilli flakes and whatever else you may find, but it’s the Cajun that’s the main ingredient. If raw fish isn’t your thing and you prefer to have your fish or meat a little more on the cooked side, there many options you may like to try or experiment with tuna fillets or steaks. When you ‘fillet’ or ‘flake’ your tuna loin, you should always do it along the grain of the flesh with a good sharp knife. It should be pretty straightforward to slice it off into nice eating sized fillets. I never cut tuna across the grain if I’m going to cook it as it looses all its moisture and flavour. You may like to try it marinated for 30mins in soy sauce, sesame seeds and ginger and seared on the barbeque or simply cooking it in the breadcrumb mix mentioned earlier accompanied with some lemon and sweet chilli sauce. Another really nice one is Pepper-seared Yellowfin fillets accompanied with horseradish sauce. Dicing tuna into 2-3cm cubes and having them on the BBQ as marinade kebabs tastes really good to, especially if your lucky enough to have some scallops as well. I recently had yellowfin cubes in a curry as a substitute for chicken. As long it’s only added for the last couple of minutes and it doesn’t over cook, it tastes great. I’m sure you can come up with your own recipes and varieties for tuna as there are endless marinades, sauces and tasty recipes available on the Internet today. Whatever you choose it’s important not to over cook tuna as it dries out and looses its flavour easily. Besides tasting great, tuna is really good for you, tuna is abundant with Omega-3 oils, is low in calories but very high in protein, iron and vitamins A and D, so it’s no secret why the Japanese and Hawaiians hold it in such high regard. It’s a shame in some ways; many New Zealanders don’t take the same amount of care as our overseas friends. Tuna can be some of the nicest fish in the ocean to eat, or it can simply be terrible if it is not processed and looked after properly. Hopefully this will help out during summer and give you a few more options. You may want to take a little extra time to process the tuna correctly that aren’t required at the weigh station. If you do want to weigh your fish, maybe consider a good fish bag and some ice for your days fishing, I’m sure you’ll taste the difference…Good Luck!