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Originally Posted by wiredantz
What do we know about this species? Jim? 
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Ha Ha ha ...... I don't know much about them, and never seen one. I know they are around here but deep. Great video by the way. I once saw one of it's relatives a Ribbonfish while at anchor at Catalina, and it swam the same way. Cutlasfish if you know what they are can swim like that as well.
So since almost nothing is known about them I can only give you my theories on how they live and even hunt, because believe it or not I'd say that fish is a hunter.
I like to think of animals in mechanical terms. So something as weird as that creature is obviously adapted to do something specific. So the question is what is it adapted to do?
I'd say it's an open water ambush predator that feeds on things getting washed down to it by the current, that holds in the current then uses both it's vision and ability to pick up vibration to pick off small fish, crustaceans and invertebrates that are washed down to it.
The long body is a cool adaption and I'd say it does two things.
The first you can see in the video.
It hangs like a knife or a like a thin bladed rudder in the water which reduces drag. It's probably has a very short intestinal cavity so the swim bladder keeps it head up while the rest of the body acts like a weighted keel. It's thin and it holds it body rigidly still. The only movement is the dorsal which pushes it forward enough to hold in the current using the same principles of a Hobbie drive in that as it moves the dorsal side to side the flex in the fin creates force which pushes it forward. It's like sculling a fixed keel sailboat forward with just it's rudder. Simply put this is a super efficient way for a fish that large to hold itself in one place in a large moving ocean current.
Like your average fillet knife from the side it's easy to see, but turn it with the edge towards you and it's not very visible. So say you were a fish or shrimp getting washed down current directly towards it. There wouldn't be that much to see and since it's metallic silver what you could see would reflect the color of the water around it so it would blend in, and not be very visible at all.
I've seen whole schools of cutlasfish in the Gulf swimming and hunting like that, and I've watched them feed. Cutlasfish are different with larger mouths and teeth but their body structure is very similar.
Note the big eyes, similar shape, and similar coloration.
They hang vertical using only their dorsal to hold position in the water but they can rapidly move up or down when they use their whole body to move.
The way they hunt is they sit still until something get's close then they will suddenly shoot up about half their body length like a striking snake to grab passing fish or shrimp. They will take spoons or small lures, and once hooked actual fight pretty hard for their size by trying to swim backwards directly away from you. We used to fish for them all the time as they are excellent Kingfish bait.
I imagine this fish feeds the same way. it's an open water ambush predator that feeds on things getting washed down by the current. It has large eyes so when there is light it has good vision for hunting or locating prey that's washing down to it. The also have several very long almost hairlike fins that I imagine they use to pick up vibrations in the water so they can hunt in total darkness as well.
All and all I'd say it's a pretty weird but actually a pretty amazing adaption.
Now your not going to find any of that in a peer reviewed journal but that's how I'd say that fish survives.
Speaking of things no-one knows I think that fish does have some kind of predator that attacks them. In every picture of seen the tail section looks like it's been chewed off at the end. I used to think that it was only the case for dead ones since most of the pictures I've seen are of ones that died then floated to shore. That said if you look at the video those oar fish are missing pretty good portions of thier tail as well.
Here's a pic of one of it's closest relatives a ribbonfish that was photographed at Catalina, that still has it's tail. I imagine the Oarfish has a similar tail structure when whole.
Pretty similar fish. Notice how it's holding in the current and though it's dorsal is pushing it forward it's long fins are trailing back almost like antenna, which to me suggest that it uses not for mobility, but to pick up vibration in the water for locating danger or prey..
Cool fish!!!! Weird but pretty amazing in my book.