The toughness of the fish you catch depends only on the level of your "fishing expertise" skills. If you train that to the max possible lvl, you will be having a lot of trouble fishing with a D rod. My advice to you is raise expertise slowly, but not above what you can handle. also keep pupming and reeling skills 2 levels above the expertise. Using fishing shots will allow you to raise mastery a little , compared to not using. Decide weather you want to be using them or not, before lvlin expertise.
If you mostly hunt in a field you will have no problem with getting fishing shots. I got close to 1k hunting 1-2x mobs solo and mostly shot-less with a lvl 40 WC.
And i heared people using nograde rod with fishing expertise skill up to 15 or something.
If you maxed out your skills and use a D grade rod you will use alot of shots to catch the fish. I am using a B grade rod and use between 3 and 5 shots per fish. I catch 90% but some still get away.
Would have used A grade fishing pole but dont want to spen the 5 mil it cost for the pole.