There is a bug with Optifine Ultra and Standard (I've tested with the latest versions), causing the fish to not move and to glitch out if you try pushing them if they are within 8 or so blocks from you.

In the 1.7 version I found a work-around (which can be disabled in the config file if it causes any problems).

In the 1.8 and 1.8.9 versions, set Smooth World to false, and it should work.

By myself (Tmtravlr)

Here are all the major crafting recipes in the mod:

Iron Nugget (should be compatible with any other mod that uses iron nuggets)

Iron Fish Hook

Wooden Fishing Rod (different from the vanilla fishing rod)

Iron Fishing Rod

Gold Fishing Rod

Diamond Fishing Rod

Baiting a Fishing Rod (surround it with any type of seeds)

Fish Tank

All right, so you see some fish in your world... so what do you do with them now? Well, there are several things. The simplest is you can go and stab them with a sword to get the fish item directly. They aren't so easy to spot though, and they have small hitboxes (and drowning is always a thing), so it may be easier to fish them up with a fishing rod instead...

Note that the vanilla fishing rod won't work; it must be a fishing rod from this mod. If you try fishing normally with a vanilla fishing rod, you will get "fish bones" in place of any fish you would have caught (you can disable that in the config file).

There are four fishing rods: a wooden, gold, iron, and diamond one. They follow the other vanilla tool sets in terms of durability and enchantability. Simply throwing a fish hook near a fish isn't good enough though... you have to put bait on the rod, using seeds (crafting recipe above).

So cast your fishing rod, and wait for the fishies to come! You can also fish up the same treasure/junk as the vanilla fishing rod if the hook sits long enough without a fish biting. Also, a word of warning. If you pull on the fishing rod too much at once, it will break. So you must reel the fish in a bit at a time, instead of spamming it.

If you have a bucket of water in your hotbar when you catch the fish, the fish will go in the bucket. You can then release it, or place it in a fish tank (more info below). You can also rename the bucket containing the fish in an anvil to name the fish without having to use a nametag.

So you want to make a fish farm, huh? Well why not?

If you want to make a fish farm, you should first make some fish tanks (recipe above). The fish despawn naturally unless they are inside of a fish tank, so that way you don't have to name every fish in your farm. =P

You breed the fish with seeds, but instead of clicking the fish with the seeds, you throw the actual seed items into the fish tanks, and the fish swim to them and eat them. So you could even make an auto-farm using dispensers with the seeds! =)

The fish will spawn in several biomes:

Cod will spawn in every biome type.

Salmon will spawn in rivers, swamps, and oceans.

Pufferfish and Clownfish will only spawn in oceans.

-Big thanks to EzerArch for the Portuguese translation files

-And also to Larsii30 for the German translation files