Calusa makes a good cast net. As far as net size, mesh size, and net weight. That is going to depend on your ability the throw the net and target species.
If you going after pilchards, you’ll want a 1/4" or 3/8” mesh at whatever diameter you can effectively throw.
If you going after mullet, you’ll want a 1/2” or 5/8” mesh at a diameter you can throw.
Another dimension to consider is weight. You’ll find nets from different manufactures with differing quantities of lead. My 12’ - 3/8” pilchard net, for example, weighs in at 22 lbs and sinks plenty fast. But, it’s a big net to throw repeatedly.
Give
Calusa a call or go to their web site. I believe you can even view a video on, "
How to Select a Cast Net" online.
http://www.calusa.com/howtothrow.cfm
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--- General George S. Patton