Trading in fish is very safe yet can still pull in a surprising amount of value. Plus, fishing rods are a default BP and bait can be found basically anywhere. Most of us learn pretty quickly that you have to fight the fish to catch it, but if you peel things back 1 layer you can really optimize your catch rate.

It is possible to build some advanced setups that allow you to very easily or even instantly catch the fish. Though they are quite complicated and fiddly, I've personally done it with ramps in a steep part of the river. Another user found a more reliable, but lengthy, way to do it. If you're curious here they are:

You can aim up to 180 degrees away from the bobber up close (within 1.2 meters), but only up to 60 degrees away from the bobber at a distance (beyond 1.2 meters)

If the bobber "escapes" beyond 2 times the cast range (20 meters), the server cancels the fishing attempt.
If the player moves one meter from their starting position, the server cancels the fishing attempt.

The fish will alternate between resting and pulling. The rest timer is 2-4 seconds, scaling up with the fish's fatigue (the more tired, the longer it rests, up to 4-8 seconds), and the pull timer is 3-7 seconds, scaling down with the fish's fatigue (the more tired, the shorter it pulls, down to 1.5-3.5 seconds)

Fish fatigue is a value between 0 and 20. The fish starts perfectly rested.
Fish fatigue only increases if you're either pulling left or right (reeling has no effect).

If you're pulling sideways to the same direction the fish is going, you increase its fatigue by 0.8/s. If you're pulling sideways opposite of where it's going, you increase its fatigue by 1.25/s. You can tire out a fish by "following" its sideways movement for long enough, but counter-acting its movements is going to tire it faster, at the cost of rod strain (explained below).

The fish "rests" at 0.1 fatigue/s only if you're not pulling to any side - reeling once again has no effect.

The fish will always pull to a side (50/50 left/right), and will attempt to swim away with a 40% chance only if it's within 8 meters of you. Beyond 8 meters it will only pull left or right.

The speed at which you can reel in the fish depends on its fatigue - you can reel it in up to 3x faster if it's fully fatigued. The other factors impacting the reeling speed are the fish/item's "resistance" to being pulled.

If you take over 120 seconds to catch it, the server will force break the line.

* STRAIN MECHANICS *

Depending on what you and the fish do, the game adds different levels of strain to your rod. These values are in "units per second", explained more down below.

If you're reeling while the fish is pulling away, the strain is 1.5/s.
If you're reeling while the fish is only pulling to the side, the strain is 1.2/s.
If you're not reeling, but counter-acting sideways movement (pulling right while fish is pulling left or pulling left while fish is pulling right), the strain is 0.8/s.

On top of all that, if you're reeling in while the fish is not idle, the strain is increased by 1.0/s.

The strain value on your fishing rod decays at a rate of 1.5/s if you're not making any action (pulling in either direction or reeling).

If your strain level reaches 1.5, the rod starts creaking, and if your strain level reaches 7, the line snaps.

* Other things *

Once you reel in the fish within 0.5m of you, the catch is successful, and you gain the item.

The fish you'll catch is pre-determined when you cast, and the timer until something hooks is 10-20 seconds of base delay, and is affected by both the item/fish you're catching, and the bait you're using (different things take different times to "bite", but better bait makes them bite quicker). The final hook timer is 3 seconds at minimum, and 20 seconds maximum.