Hook sizes are confusing. Although the size system is pretty much universal, the actual sizes of the hooks for a given stated size varies from country to country.
Where there is a single number quoted, the lower the stated number, the bigger the hook, so a size "20" will be so small that a matchstick will barely fit into the gape (the gap between the point and the shank) whereas with a size 2, the gape will be about 1cm. for bigger hooks, the sizing system changes and will be shown as "1/O", "2/O", "8/O" etc with the hook size getting bigger with the size of the number preceding the "/O".
Next thing is the thickness of the wire. Fine wire super sharp hooks are fine for American bass fishing, but for barramundi, mahseer and the like, these aren't much good so you need hooks with thicker and strong wire. This is expressed in terms of how many times stronger it is than the standard wire, so you will see hooks advertised as 2x, 3x, 4x or even 6x.
Then there's coatings and materials. "duratin" coatings or stainless steel hooks will survive saltwater better but in sweetwater, a simple bronzed hook might be a better choice because although it will rust, all of the weight of the hook is steel and it will be much stronger for a given weight or wire diameter.
The upshot is that for barra fishing, something like size 1 or size 2, 3x trebles with a duratin coating might be a good choice.
For big GT poppers, you might want much bigger size 2/O or 3/O hooks rated as 4x or even 6x strong, again either stainless or duratin coated.
For replacement hooks for spinners that you use for trout, fine wire (1x) size 8 trebles that are either bronzed or tinned (shiney silver) would be a better choice.
Hope this helps.