Gear Maintenance

Introduction

Spearfishing gear is subject to salt, sand and other elements of nature, proper maintenance is needed if you want to keep it functioning optimally for a long time. One of the main two culprits to watch out for is salt and direct sunlight, it will kill some of your gear in a matter of weeks or months if you do not remove all traces of salt from your gear and keep it out of direct sunlight. 

The most important thing to do after after each time you use is to rinse your gear thoroughly with fresh water. This can be done with a garden hose, in the shower (using a removable shower head) or in the bathtub. If I am going out again next day I usually just rinse it real well with the hose/shower head and let it dry (out of the sunlight). If I will not use it for a while, I do as described above and then I fill the bathtub with lots of fresh water and put in all items that sink and let them soak well for several hours (changing the water at least once). It is important to make sure the gear is well dried before long storage.

I will go through the list of gear most spearfishermen have and share what I do to keep it in a good shape.

Speargun

The speargun is the most complex gear you own, it is also the most important item (you can get away with not having anything else if the need be). Spearguns can oxidize due to salt and air (or even simply the contact of some of the metals that they are made of (e.g. aluminium + stainless steel), the mechanisms can lock up due to oxidization or sand, wooden spearguns can warp, bands/slings can degrade, etc. As mentioned in the introduction the most important thing to do after a hunting session is done is to rinse it well. Special care must be given to the mechanisms (trigger, line release, reel), I try to inject as mush water inside it via the multiple openings as I can. If you put it in the bathtub make sure the spear is on the speargun so it sinks and I let it soak well for several hours. I also make sure I rinse in between where the slings are in contact with anything to remove anything that could help to degrade them during storage. Also important is to make sure it is thoroughly dried to reduce any oxidization. It is also a good idea to take the spears out of the mechanism for longer term storage. Once in a while (I do this every two or three years) you can clean/oil the trigger and line release mechanisms. If you are not comfortable taking apart your speargun then just inject some WD-40 (not too much!) inside the mechanism using the "straw"). Be very careful not to get any on the bands/slings as it eats/degrades rubber (think of what you learned in sex-ed about Vaseline and condoms, same issue!).

Slings/Bands

I have pretty much summed it up on these in the post above (speargun), but I would also add that sunlight is very bad for rubber. It is recommended to store them in a cool dry place out of light. Some people use silicon grease to keep them supple and others go as fare as putting them in a zip-lock bag (make sure there is not humidity inside) and store them in the refrigerator. Some say that the ideal temperature is between 10°C and 25°C and should be stable. Ozone is also bad for the rubber so watch out for this, ozone more prevalent in hot & sunny periods and in smog.

Shaft/Spear/Points

Cheap shafts & tips are made with "standard" stainless steel. This is great for oxidization but not so good for hardness (they deform/warp easily). The good ones are made of a different type of stainless steel, often 17-4PH hardened stainless steel (or something similar). This type of steel resembles SAE 304 in terms of corrosion resistance, which means it is not as "rust proof " as the cheaper stuff. A thin layer of oxidization can form on it but it should not corrode like non-stainless steal. To keep it rust free I do the following:

1. Rinse it well with fresh water
2. Dry it well
3. Put some WD-40 on a rag or paper towel and rub it well against the metal

The idea with step 4 is to deposit a thin layer of WD-40 on the metal to protect it. WD-40 also removes any oxidization that could have already started. When I get ready to use it I rub the metal with a clean rag or paper towel to remove it. As mentioned in the speargun section of this post I recommend storing the shaft off the speargun so any oxidization from either does not contaminate the other.

Reel

If you have a reel make sure you rinse it well. I like to let it soak in the tub so the salt leaves the mechanism and the line. I also inject water where there are small spaces. Let it dry thoroughly, this can take a while with braided line.

Knife

The knife, if not made from Titanium, can rust also. Some knives have a layer of Teflon on most of the blade to prevent oxidization but in some places such as the cutting edge or the region where the blade goes in the handle, rust can form. As with all the gear rinse and dry well, but also use some silicon grease to protect the blade when you are not using it.

Mask

The mask sounds like a no-maintenance item and it mostly is, you can just rinse it well. I like to clean the inside with some toothpaste as mentioned in my "Mask fogging up?" post. I usually let the toothpaste dry so it protects the inside from any oils and when I want to use it I just let it soak in the water a bit and shake the toothpaste out.

Neoprene (wetsuit, socks, gloves, etc)

The wetsuit requires special care too. I rinse it very well and let it dry out of sunlight. UV light degrades rubbers and Neoprene is essentially rubber with nitrogen bubbles in it. It is important to dry it inside and out; if you do not mold could settle in and this is very hard to remove (and it stinks!). I have read that you can wash a wetsuit if it starts to smell (mine never have). Some people just use a little laundry detergent (the kind you use to hand wash wool/silk) mixed with water in a tub. Just rub the neoprene well, let it soak some, rinse well and dry. I have even read some people sick it in the washing machine on the delicate cycle (the one for wool) and let it run (using the same type of laundry detergent). I am not sure I would try, I guess it depends on if the first method failed, but if you do try make sure the temperature and the spin is low (it should be if you have a dedicated wool cycle). Never, I repeat, never use the drying machine! To store a wetsuit is is best to lay it out flat in a cool dry place out of light. You could also try one of those wetsuit hangers but since apnea wetsuits are more elastic than scuba wesuits you could get some deformation from the pull of gravity. If you have an open-cell wetsuit, try to keep the rubber from touching itself to prevent it from sticking. You could for example stuff it with cloth.

The rest of the gear

The rest of the gear is essentially minimal maintenance, just rinse & dry well and store in a dry dark place.

Conclusion

If you rinse your gear well after every use and store it correctly it should last you much longer than if you do not. As with everything is is a question of inverting time to care about your investment but sometimes circumstances make it harder to do it well. In this case just stick to the minimal maintenance which is: rinse & dry well and keep out of sunlight.

As with all my posts, if you have questions or comments please don't hesitate to write below in the comments section!

Review: Omer Laser Mini Knife

Introduction

I had a dive knife already, the XS Scuba Beta Titanium Knife. It is a good knife generally but the tip is not great for braining fish, as explained here. It is also too long for that task and another issue is it is quite big and can get tangled up in line or algae (I carry it on my leg). I mostly use it for:

• Braining fish
• Cutting up bait fish
• Gutting my catch (I do that in the water right after braining it)
• Cutting line
• Digging my spear out if tight spots

I decided to look into getting a proper braining knife, I was looking for:

• Small size: allows better control
• Sharp stiletto point: slides right in the fishes head, even fish with hard skulls
• Serrated on one side: it is useful if you have to saw anything, like bone
• Stainless steel or Titanium: I don't want a high maintenance knife
• Flat profile: so it doesn't attache itself to everything when not being used
• Robust but easy locking mechanism: this keeps the knife from falling out but if it is too complicated it can hinder using it.
• Arm band: I wanted a quick access knife

I decided that for now I will keep on bringing my bigger knife for the reasons I listed above and have the small knife mostly for braining. I narrowed down the list of knives to:

• Salvimar ST-Atlantis Knife
• Riffe Silencer
• Extrema Ratio ULTRAMARINE
• Speardiver Skene Spearfishing Knife
• Beuchat Mini Mundial Knife
• Omer Laser Mini Knife

The Salvimar ST-Atlantis has most of what I needed, except the arm band and that it is made to go on a belt. It has an interesting handle strap but I wondered if that could not get in the way. It looks like it can be useful to hold the knife in a stabbing from above or in front but these aren't things you usually need to do underwater. I couldn't find anything (reviews) on the locking mechanism either. I decided not to get it because of those reasons (missing arm band, no locking mechanism reviews & possible hindrance of the handle strap).

The Riffe Silencer looks like an excellent knife, it has everything I need but I read several reviews of people that lost their knife because the locking mechanism failed, this is why I did not get it.

The Speardiver Skene Spearfishing Knife is a great knife, it has everything I need but I was not moved by the locking mechanism. It is simple, yes, but I am not sure I would trust it. I am sure it is great though but I didn't want to take a risk.

The Extrema Ratio ULTRAMARINE is just a beautiful and functional knife, it has everything I need but it is extremely expensive (€549.50!), this is why I did not get it.

The Beuchat Mini Mundial was not as flat as I would have liked and looked cheap; I also found the locking mechanism not as convenient and easy to use one handed.

That left me with the Omer Laser Mini which had everything I was looking for:

Specifications

• 8cm blade
• AISI420 Stainless Steel Blade
• Squeeze Lock Positive Retention Mechanism
• Serrated and flat blade
• Stiletto blade shape
• Arm Holder Sheath

Build

The build quality is very good. Being a only knife you would think this can be taken for granted but many knives (diving and non-diving) don't have a good build. The locking mechanism is usually where some dive knives fail in quality but here it is good, I will see how it fairs after a couple of years of usage.

Blade

The blade is partially serrated on one side and flat on the other, it has a stiletto profile:

It is made of AISI420 which is a rust resistant stainless steel (but not rust proof). This is because the more rust resistant steel is the harder it is to keep an edge (i.e. dulls fast) because of the high Chromium and low Carbon as explained here. It has a Teflon coating on the blade (except on the edge) to protect it from rust (like the Ka-Bar US Marines knife has), this will however were off after a while. I was more inclined to a stainless steel blade instead of a titanium blade. Titanium is light and keeps an edge but it is difficult to sharpen and I'm always afraid it will snap (this is purely psychological). The blade does not have the line cutting notch, this may be a problem for some people but I don't mind so much as I can use either side of the blade or even my big knife which has it.

Handle

The handle is very flat:

here is another picture:

I cannot say it is very comfortable to hold because of its flatness and also because it is not very long. I wanted a knife mostly for braining fish, gutting them and the odd line cutting if tangled, for this I don't need to hold it a long time. Its flatness also means it is closer to my skin and less likely to get caught up in line and algae.

Locking mechanism

The locking mechanism is on the sides (the grey parts):

to release you must push on both sides and to engage just slide the knife in. I think it is a quite natural way of unlocking the knife as I don't have to do anything special other than squeeze a bit when taking it; I can have a good hard hold on the handle at all times and take it out one-handed. A safety on the front part of the sheath like lots of knives have makes you have to press it either with the other hand or hold the grip with two fingers and use the index to push; in certain circumstances you could lose hold of the knife (struggling, panic, etc).

Arm Band & Sheath

The arm band is great, it even protects your arm a bit around the sheath:

Personally I like it a lot, however some people may not since the sheath is permanently affixed to it (e.g. you can only use it on your arm or bottom part of the leg). It has a rubber strap to attach and tighten it. It used to have a Velcro strap but it apparently slid down too much. I do think they could have used a different type of attach-point/buckle because it is not great to put on or take off quickly. It does however not fall off or slide down so I guess that is the most important part since you only put it on and take it off once action per dive. The special strap/sheath is actually one of the points that made me choose this knife.

Maintenance

It does require a bit of maintenance since it is not 100% rust proof or titanium, but it is not much more than what I usually do:

• Rinse it well every time in fresh water, including the sheath (I already do this to all my stuff)
• Dry it well after rinsing
• Use a bit of silicon lubicant when storing

Conclusion

I am very happy with this knife, it does everything I need. Like I said above it is just missing the line cutting notch and has a little maintenance but it is well worth it. I recommend this product.

Spearfishing safety

Introduction

In this post I will speak of spearfishing safety. I will mention safety guidelines towards others and for yourself.

Safety Issues

First and foremost, you should never spearfish alone, you need to find a dive buddy with whom you feel safe, both of you need to know what to do in the event of a problem. The types of problems you can encounter are (in no particular order, there are others):

• Shallow Water Blackout (SWB): this is were your body no longer has enough oxygen, you blackout usually swimming back up to the surface or even after you have reached the surface and breathed fresh air. This is IMO the most dangerous thing that can happen because it gives no warning at all, your body doesn't react to not having enough oxygen but instead reacts to having too much carbon dioxide (this is what triggers the urge to breath) and you never realize you don' t have enough.
• Getting tangled in some sort of net, line, etc: this is another way to drown, it can easily be avoided though if you carry a knife or scissors.
• Getting stuck in an underwater cave: this can be avoided also by simply not going into caves, if a big fish swam inside then too bad, you weren't fast enough and it won, get over it.
• Strong underwater current: this is harder to avoid since you cannot see it before swimming into it. If you get caught in one try to swim up quickly and beware of rocks.
• Sharks: these are a problem in certain parts of the world (mostly tropical and sub-tropical).
• Getting bashed on rocks: this can usually be avoided by not going in rough water, it is a bit trickier when you get swept up by a strong current.
• Boats: in most places you have the obligation to have a buoy with a dive flag, this warns boats you are in the water, the boats should stay more than 50m from a buoy. This is the nice and dandy theory, unfortunately some boat captains either don't see the buoy or don't care. If you encounter those then if you can take a picture of their identification number and report them to the authorities. I am not saying this to be mean, but this is dangerous for you and they will remember to look (and respect the distance) when confronted by the authorities, I know, it sounds lame, but this is your and other spearfishermens' lives in danger and as a captain they are required to respect this, just like a car driver has to look out for motorcycles, bicycles and pedestrians.
• Your dive buddy: this may surprise you (or not), but many accidents involve your buddy shooting you. As a general rule you should never point your speargun towards a human being, you should always have the safety one until the last possible moment (before you shoot, this is easier with some spearguns than others, see my speargun post's section on different speargun brands' safety mechanisms) and you should never have a loaded gun outside of the water (this is often by law). It is also recommended that you hunt with one gun and take turns, when one is below the other observes him/her. This has the added safety that you rest and get your oxygen levels up again (to help prevent SWB) and you can react if your buddy gets in trouble. Some people hunt one in from of the other with a big distance in between each other, others hunt in parallel also with lots of distance. When the water is murky it becomes more difficult. You should use the same safety rules as you would when using a firearm.
• Hypothermia: this is a problem mostly in cold waters and when you don't wear the correct wetsuit. In reality it can happen even in tropical waters if you stay long enough, the water is colder than your body temperature and has higher thermal conductivity than air so it will literally suck the heat out of you. Most of the time you can be safe by not going in in cold water without the proper equipment and by not staying longer than you should.
• Cramps: this can be a problem if you are under water. There is no sure way to prevent this or know it is coming, you can only eat potassium and magnesium regularly to help guard from it but that is all. I read of a person who had this happen to his legs and he used his DSMB to get back to the surface.

Safety equipment & guidelines

There are some guidelines and equipment you can have to make spearfishing safer (by problem):

General

• Quick release weight belt: this is a good idea to have, most weight belts are like this. It means that if you have an issue and you have to swim up as fast as possible, you can quickly drop your weight belt. For this reason I would not up anything expensive on the weight belt, some people put their dive knife on it but they could hesitate to drop the belt because if that. YOUR LIFE COMES FIRST, your dead body has no use for a dive knife. Here are examples of a SCUBA type belt (left) and a spearfishing (Marseillaise) belt (right):
  

Shallow Water Blackout (SWB)

• Freedivers Recovery Vest (FRV): this is an inflatable life vest that is triggered by either going too deep, staying too long under or not confirming you are conscious after reaching the surface. It is a bit pricey but worth it, especially if you are a bad boy and dive alone. It will bring you back to the surface and flip you on your back, see here for more info, have a look at these pictures:
  
• Dive computer: a dive watch with depth alarms, dive time alarms and surface recovery alarms; these are different from SCUBA dive computers. Some SCUBA dive computers that are wrist watches have some of these functions, like the Suunto D4i. Other dive computers are specifically made for freediving, like the Aeris F10v2, Aeris F11, Beuchat Mundial 2, Mares Nemo Apneist, Sporasub SP1 Freediving, Sporasub SP2 Freediving and Cressi Edy II. The alarms allow you to understand where you are in regards to know your depth (how long it will take you to swim back up), time under (an idea of how much oxygen you have left), surface recovery time (how long you have to wait until your next dive to be fully oxygenated).

Sharks

• Using a buoy with a stringer: this keeps your catch away from you, the best is to have two buoys, one for the catch and one for yourself. If you have you catch in the water, they will go after it, this is why YOU SHOULD NEVER CARRY YOUR CATCH ON YOU. If you can, always keep your catch out of the water in places that have lots of sharks.
• Stay calm, if you are agitated and move in a distressed manner they will be attracted to you. They are curious animals so just because you see one doesn't mean they want to eat you; most of the time they scope you out and leave.
• I don't recommend trying to stab, shoot or spike the shark unless it is of last resort, sharks are curious animals and will swim close to you to check you out. If they come too close, you can prod them with the metal tip but not stab them, stabbing or shooting them will only make them mad. Usually the contact with something metallic will make them less curious.
• Having a metal spike attached to the gun's muzzle can help you detour them, some spearguns have this by default. This is useful because if the spear is not on the speargun and a shark shows up you have the spike to help keep the shark away. I would use a line setup that allows you to keep the gun once you have shot a fish, either with a reel (and lots of line) or a breakaway setup. A good example of a shark safe gun is the Speardiver Carbon Elite Speargun (no longer available):
  
  Shark spikes can cause other issues though, they are dangerous. For example if you shot a powerful fish and you are handling it via the shooting line and it darts off, the line will slide through your hands and the speargun could stab you in the back, legs or even head. A safer solution would be a retractable shark spike, see here for a discussion concerning this.
• You can have powerheads for last resort if you get a shark that does not get the point, these are essentially aluminium cylinder that fire on the point of your speargun and have a bullet at the end. The spear point acts like the firing pin and will detonate on impact with the shark. There are reusable types and one use types. The one use types are supposed to be less prone to misfiring since the bullet is fully encased/watertight (they are anyways a last resort safety feature, a bit like an airbag in a car). Reusable types allow you to use them several times as the name implies but you should use a new bullet each new hunting session to be sure your bullet will work when needed. Here is a good example of one-use powerheads (Speardiver Quick Slip-on Powerhead) with a convenient pouch (Speardiver Powerhead Belt Pouch):
   
  and also Neptonic's new newly designed reusable K.O. Powerhead with has a dual safety design: 
  

• Having a knife: don't get excited, this will almost never be of any use, sharks are too fast and you are safer further away from them, but push comes to shove...as a last resort.
• Boat/shore: yep, get out of the water but do not turn your back to the shark.

Boats

• Buoy, flag & floatline: this can be attached to yourself or to your speargun. If you attach it to yourself be careful about becoming tangled/attached to something. If you attach it to your speargun it helps you from losing it in case you shoot a big fish but you could become separated from the buoy in this case, both have pros and cons. either way the boats can see you are around and steer clear. See here for more info.

Tangled

• Knife or scissors: in case you get caught up in something you can cut your way out. See the info about the quick release weight belt above and look here for more info about knives.

Hypothermia

• Wetsuit: an adapted wetsuit will guard against this, you will still be limited on how long you can stay in the water depending on the quality of the suit, its fit, the thickness, the density of the neoprene, the type/cut, dry/semi-dry/wet, etc. Beware of overheating however! See here for more info on wetsuits.
• Boat/shore: get out of the water, if your wetsuit is lined you will lose more heat with the wind so either wear a wind breaker, get out of the wetsuit and into cloths or go inside.

Cramps

• Delayed Surface Marker Buoy (DSMB): aka CO2 inflatable safety sausage, this can be useful to go back to the surface in case you have a cramp or if you have to bring your buddy up fast. See here for more info. Here is an example:
  
• Freedivers Recovery Vest: (see Shallow Water Blackout above), it has a manual inflation latch:
  

I hope this information is helpful to someone, please correct me (add a comment) if you see something wrong and add comments or extra info.

Spearfishing Knives

Introduction

Another piece of gear that is useful is a knife. This can be used for the following reasons:

• To "brain" (kill) a newly caught fish
• To cut line, a net or kelp if you get tangled
• To gut/ clean a fish
• To dig your spear out id certain cases if it gets stuck
• I guess you could also add to defend yourself
• Some knifes allow you to straighten your spear or leverage it
• It looks cool :-)

There are different types of materials, shapes, sizes, etc; so it is not an easy choice! Here is an image describing the main parts of a knife:

Source: http://www.leisurepro.com

Blade Materials

This is an important thing to think about, it will determine the weight, robustness and corrosion resistance of your knife. The following are the main types:

• Steel: Cheap, heavy, robust, maintains a sharp blade, easy to sharpen, but rusts, must maintain it very well by rinsing it with fresh water (as you should with all your gear), dry it, grease it and store it in a dry place.
• Stainless Steel: Heavy, robust, maintains a sharp blade (more than Titanium), easy to sharpen, corrosion resistant. There are two types generally used for dive knives:

        - 300-Series: More corrosion resistant but it loses its edge quicker
        - 400-Series: Stays sharper longer but more susceptible to rust

• Titanium: Expensive, Light, fairly robust, maintains a sharp blade (less than SS), a pain to sharpen, the best corrosion resistance

Number of blades

A knife can have one side that cuts (I will call this one blade) or two (I will call this two blades). Most spearfishing knives have two blades. The advantage of one bladed knives is if you have to be able to press on it to cut though thick things, this is not really needed for spearfishing though. A two bladed knife can have a mixture of blade types in one knife, see Blade Type below for more info.

Blade Type

There are two types of blades:

• Straight: the conventional type, it is used to cut fine things such flesh, fishing line and other fine lines. If you only have one blade on your knife it will be of this type 9 times out of 10.
• Serrated: this is like a saw and useful to cut through tougher things like bone, rope, kelp, etc. They tend to stay sharp longer but are a pain to sharpen (sometimes impossible).

Size

Size matters ;-), but not necessarily the way you think!

• A long blade is useful for self defense, cutting fillets, as leverage, etc.
• A short blade is good for stealth and it makes it easier to brain a fish.
• A thin knife (including handle) is good for stealth and hydrodynamics but is less comfortable to hold.
• A thick knife (including handle) is comfortable but can get caught up in kelp, line, nets, etc.

Curvature

You can have either curved blades of straight blades, it is mostly a preference and often depends on the tip type and usage.

Blade Point/Tip shape

Here are the main types of knife tips you will encounter in diving/spearfishing knives:

Knife tip types

1. Clip point: This is the shape of most hunting knifes, the tip has a clip taken out of it on one side. It is usually a one bladed knife and seldom used for spearfishing.
2. Drop or Spear point: these are actually two different points but I grouped them together since they have the same shape. The difference is the drop point only cuts on one side. They are shaped like a Swiss army knife blade. Some people like them but they are hard to use to brain a fish with a hard skull due to the rounded curvature of the blade. I have one (on my ankle) with a long blade (13cm) that I use to gut fish, cut my way though things, dig (since the point is still strong due to its shape). This is a common shape for spearfishing knives.
3. Needle-point (aka Stiletto): This shaped live a thin V, it is very efficient for braining fish and cleaning them. It is however more fragile at the tip than the other knives. I have a small one (8cm) on my biceps that I use almost exclusively for braining and gutting fish. This is a common shape for spearfishing knives.
4. Blunted: the tip is flat and may or may not cut, this is very useful if yo have to dig things out & pry things open since sharp points can break. It is however harder to use if you need to gut a fish or stab something. They are rarely used in spearfishing.
5. Tanto: This is like the tip of certain Japanese knives, the tip has very square lines. You can see it as a mix between the blunt tip and the spear point tip (the good sides of each). It is seldom used for spearfishing however.

Position on the body to wear knives

Where to put a knife? It is mostly a personal preference, the main spots are:

• Calf: Most common, easy to grab. Possible to grab with both hands if necessary. It can get caught though when you are swimming though kelp, nets, line, etc. Can be worn on the inner calf to offset this last point but can then rub against the other calf.
• Thigh: Possible to grab with both hands if necessary. May be uncomfortable since your thigh muscles work out a lot.
• Forearm: Can only be grabbed with one hand, on the opposite side. If you have a dive watch it could make it harder to grab.
• Biceps: Can only be grabbed with one hand, on the opposite side.
• Belt: Possible to grab with both hands if necessary.The issue with putting it on the belt is that if you have to quickly release it (weights) you lose your knife. The through of this could make you think twice, thus endangering your life. I think it is therefore better not to where it on your belt.

Number of knives to carry

So, one knife, two, more? I think one knife is the most common, I prefer to have two. The reason for this is:

• Safety: if I am stuck I may not be able to grab the knife, if I have two it minimizes this risk.
• Different needs: I use the knifes for different reasons, my small one is for braining, and gutting, the big one for leveraging, cutting lines, protection, etc. If I had to do it all over again, I would maybe take a blunted tip for the big knife.
• Backup: if I lose one (and I probably will one day) I still have another one on me.

Misc

• Coatings: Some knives have coatings, like Teflon. This protects against rust; even SS can rust in salt water (if your SS is 400-series to keep a good edge it will rust a little).
• Line Cutting Notches: some knives have a notch or hook in the blade that is used to cut line, this is very useful.
• Scissors/cutters: some blades are actually also cutters/scissors. Imagine if you sharpened a blade on the outside if scissors. This can be useful to cut line and nets, to cut through fish bone and flesh.
• Folding knives: you can get a folding knife, I personally am against this since it is not ready when you need it, they are hard to grab and can be dropped, the are hard or impossible to open with gloves. I really see no advantage.
• Knives allowing you to straighten your spear or leverage it: nice to have

I have two knives, I wear my big knife (XS Scuba Titanium: spear tip with straight and serrated blades, quite big, line cutting notch) on my calf and I wear my small knife (Omer Mini Laser: Stainless Steel, needle tip with straight and serrated blades, quite flat, Teflon coating) on my biceps.

Some knives I like

Spearfishing knives

• Riffe Silencer: hardened (heat-treated) 420 stainless steel, Teflon coating, plain edge and serrated edge, needle tip, medium (11.5cm blade). I read however that the sheath is bad ans you can easily lose the knife...
• Riffe Terminator: hardened (heat-treated) 420 stainless steel, Teflon coating, plain edge and serrated edge, needle tip, medium (11.5cm blade)
• Riffe Terminator II: hardened (heat-treated) 420 stainless steel, Teflon coating, dual serrated edges, needle tip, medium (11.5cm blade)
• Omer Laser: 420 stainless steel, Teflon coating, plain edge and serrated edge, needle tip, different sizes available (mini: 8cm, normal: 9cm, Maxi: 13cm)
• Salvimar ST-Blade: plain edge and serrated edge, needle tip, small (7.5cm blade), flat, strap to secure on hand, Stainless-Steel, shaft extractor/straightener
• Salvimar ST-Atlantis: plain edge and serrated edge, needle tip, medium (9.5cm blade), flat, strap to secure on hand, Stainless-Steel, shaft extractor/straightener
• Picasso Tiger: extremely flat (handle is bare), Stainless steel, shaft extractor, line cutting notch, shaft diameter measuring holes, medium (10cm blade), needle tip
• Speardiver Skene Spearfishing Knife: extremely flat (handle is bare), long (11cm blade), Teflon coated Stainless Steel tempered to 55-56HRC hardness, plain edge and serrated edge, line cutting notch, needle tip
• Extrema Ratio Ultramarine: very flat, super expensive, Cobalt Steel N690, line cutting notch, plain edge and serrated edge, spear extractor/straightener, spear tip.

General dive knives

• Scubapro White Tip: 304 stainless steel, blunt tip, medium (6cm blade), flat, plain edge and serrated edge
• XS Scuba Titanium: Big (13cm blade), different tips available (spear, blunted, Tanto), plain edge and serrated edge, line cutting notch, good knife

I hope this will be useful for someone! Please, if you have any comments or if I wrote something wrong, if I forgot something, if you feel some extra information would be useful or that you don't agree with something I wrote, tell me with a comment.