If you are a member, it becomes easy when your level is 16 with your cheap runescape accounts. Heading towards Catherby and you can begin to fish for Mackerel when you get there. Remember always banking your fish. If you leave them in your inventory, you will soon run out of space.
It's worth the time and you will become restorative when you sell the first bunch. 100 swordies at 200 GP each is quite a bit of change. 100 swordfish does not seem like a lot, but the reward will tell you why they are worth so much, when you get to the correct level, beginning to fish and cooking it, you will get the reason.
Unless you are only expect to raise your fishing level in your runescape account. You can reach Karamja at the Port Sarim Dock. Once you are there, following the path and you will come to a dock. Then go westwards and you will find a different dock. You can prepare to fish.
The best money is in sharks (1k each). Members only, so go fishing again is better if you are a member, as is everything else.