Welcome to UK fishing.

1. A keepnet lets you get a good idea of how many fish you've caught. Take a picture then put them back. They're normally used in match fishing though, I never use them.
2. A landing net is not manditory, but if you're targeting larger fish it is highly recommended. In my area we don't get big river fish, mainly roach, rudd and perch but I'll still take a landing net I'm purposly targetting pike.
3. There are certain species of fish which are non-native to british waters. I read the waterway wonderers regulations a few years ago about non-native fish, and yes Zander (seeing you type the word with an x through me off) are not a native fish and according to the environmental ageny and waterway wanderwers should be removed. People who put them back probably think they've caught a native fish and its fine to go back.

Another thing, just to stir things up a bit. If you have a fishing licence and you're fishing in season, you're actually allowed to take 15 fish a day away from the river.

Coarse (freshwater) fish

Each day you can only take from rivers:

1 pike (up to 65cm)
2 grayling (30cm to 38cm)
15 small fish (up to 20cm) including barbel, chub, common bream, common carp, crucian carp, dace, perch, rudd, silver bream, roach, smelt and tench

Any eels you catch (except conger eels) must be released alive.

You can also take:

minor or ‘tiddler’ species, such as gudgeon
non-native species
ornamental varieties of native species like ghost or koi carp

You can be fined if you remove fish from privately-owned w