/equip [noequipped:Fishing Poles, nomodifier:alt] Seth's Graphite Fishing Pole
/equip [modifier:alt] Mana Wrath
/equip [modifier:alt] Lamp of Peaceful Radiance
/cast [equipped:Fishing Poles, nomodifier:alt] Fishing

This macro is handy in that on a regular click (or hotkey press) it will equip your fishing pole (simply change Seth’s Graphite Fishing Pole to the name of whichever pole you use), and when pressed again will begin fishing. On an alt-click (or alt+hotkey) it will re-equip your normal weapon(s). If you use a two hand weapon, simply take out the third line and change Mana Wrath to your own main weapon, otherwise if you use two change Mana Wrath and Lamp of Peaceful Radiance to your own particular weapons. This macro also avoids any error messages from popping up. You could also add to this macro to have it swap out a Lucky Fishing Hat or gloves with the fishing enchant as well, if you had them.

Another, more simple, fishing macro is this:

#showtooltip Fishing
/cast [button:1] Fishing
/use [button:2] x y

Replace x and y with the container location of your fishing pole (bag slot and item slot respectively.) A right-click will equip or unequip a fishing pole, and a left click will cast a lure. Note though that this macro only works with two-handed weapons and not a single-handed weapon and an offhand item, shield, or weapon; if you are going to use other than a two-handed item, use the first macro.

Here is a more elaborate version:

#showtooltip Fishing
/equip [noequipped:Fishing Poles, nomodifier:alt] x y
/equip [modifier:alt] x y
/cast [equipped:Fishing Poles, nomodifier:alt, nomodifier:ctrl] Fishing
/use [modifier:ctrl] x z
/use [modifier:ctrl] 16

It will equip your fishing pole if not equipped, or cast Fishing. If you hold alt it will equip your weapon. If you hold ctrl it will use a fishing lure. The bag number is x, y is the slot your fishing pole is in, z is the slot for the lures. Again this works best if you have a two-handed weapon.

Count fish

#show Speckled Tastyfish

If you want to keep track of how many of a specific kind of fish you have, use the icon and this macro.