Your best choice for a good fishing companion knife is one of three knives... We will start with the smallest and work our way up.
BK13- Stainless steel and easily carried as a neck knife or deep in the pocket. Stainless is an obvious choice for next to water and a small handy blade that can trim line, cut knots, and even clean a fish it would be a great choice, at less than twenty dollars it would be a great blade to just carry around 24/7 or keep in a tackle box... The only cons here is its size. Its handy size can be to its detriment, and using the skeletonized blade with wet hands might make the blade hard to handle, but this should not be an issue for any avid outdoorsman, its just a thought. Once again since it is so affordable, you can purchase more than one easily without breaking the bank.
BK14-24- Both designs are excellent for an everyday blade or to just have around in a pack in case of emergencies. The benefit of the 24 is of course stain/rust resistance, but I have found rust issues not to really be a problem on KA-BAR's 1095cv hence why the 14 is added to the mix. For around 30+ bucks the 14 is not going to break the bank and its one handy SOB. Short, stout, and easily sharpened, the blade can be used to clean anything from elk to fish. Also at this price point you can add the zytel scales from KA-BAR in black or Orange, and we all know how much hunters and the alike love that bright orange because they understand the vivid color is going to assist them in not loosing the blade. If the zytel is not for you, with a few minutes of time and a length of cordage (color of your choice) you have an even cheaper and still functional handle option. I own the 24 and I know what a great blade it is for the price. It is a great performer. I would say the 11 with its bottle opener, but I know you are not supposed to have glass bottles on the water so no issues with that...
BK15- I have found this blade is an amazing companion. The swedged sweeping design is conducive to food prep, game cleaning tasks, or even bush craft. The most expensive option here I do not know of an person who would not love to have one. I carry mine with me everyday and it is amazingly versatile. I have carved traps and other bush craft tasks, used it for food prep, battoned, and cut anything from weed eater string to piles of cardboard with it. I do not consider it a small blade, but more medium to full size. The handles on the 15 come in tan or black so however its set up it can appeal to military, tactical, and outdoorsmen groups. The design is a modern representation of old roach belly trade knives, which have been a proven design through the centuries. There are users of the 15 who have reported that the 15 does great cleaning fish and game so that application has been tested. The 15 also has a great sheath with a pocket that an emergency fishing kit can be added into.
All in all I know you may have wanted a more specific answer but all of these blades have distinct benefits I wanted to make you aware of, and just to summarize them.
BK13- PRO- not expensive, small, compact, and rust resistant. Due to its price you could donate more than one, making more people happy, and even get one for yourself. CON- It is fairly small.
BK14- PRO- Super handy and tough, cordage or zytel can be added to improve its visibility, and its easy to sharpen and maintain, Black coated blade. CON- Even with its coating the edge is still uncoated, even though I have not found rust on carbon knives to be any sort of a problem, this is a consideration.
BK24- PRO- High end steel, rust resistant, will keep its edge longer, Visually attractive due to its bead blasted finish, can take the aforementioned zytel or bright cordage to improve visibility. CON- Not super easy to sharpen due to the harder steel, more expensive.
BK15- PRO- amazing blade, extremely versatile, easy to sharpen, best suited for game cleaning, full size design for comfort, would be a very, very nice give away gift. CONS- most expensive, non stainless steel.
Here are some pics of some well loved knives.
Bottom line is if you choose a KA-BAR Becker, everyone is going to be happy. Good on you for doing this.