Fish made it five tries in just two pre-season games as he scored three times in the second half, adding to efforts from Ken Pisi, Cobus Reinach, David Ribbans.
It meant Saints recovered from 10-0 down to defeat the Dragons 35-10 in the Friday night fixture at Rodney Parade.
It was a second win in as many matches at the start of the new era under boss Chris Boyd, backing up the 26-13 success against Ospreys at Brewery Field last Saturday.
But Saints certainly had to show plenty of character as they completed their pre-season training camp in Wales with a sizeable win.
Just as in Bridgend six days earlier, Saints were put under huge pressure at the breakdown during the formative stages of the game.
And after conceding ground, the away side conceded the first points, with Dragons fly-half Josh Lewis stepping back into the pocket to land a drop goal.
Saints were then hit with another blow as lock James Craig was forced off, with David Ribbans his replacement.
Backed by their noisy home support, Dragons were fired up, defending stoically and putting in 100 per cent effort on the ground to retrieve every loose ball.
And it wasn't long before the hosts had their first try.
After winning a penalty in the Saints half, Dragons moved the ball quickly and scrum-half Rhodri Williams showed good awareness and tenacity to grab his team's first try.
Lewis added the extras to make it 10-0 and Saints were struggling to get a foothold in the game.
But they were allowed to walk through an open door on 24 minutes as Pisi claimed an intercept try, prompting groans from the home fans.
Biggar converted and Saints were soon ahead thanks to another gift from their hosts.
Speedy Reinach intercepted inside his own half and turned on the turbos to easily sprint clear and score.
Biggar again put the gloss on the try with another easy conversion and Saints led for the first time in the match.
It was to remain 14-10 at half-time as the Dragons struggled to replicate their early intensity levels.
And Saints soon extended their lead after the break, kicking to the corner and rumbling over the line via hooker Fish.
James Grayson, on for Biggar as Saints rang the changes at the break, landed the conversion to make it 21-10.
Grayson was pulling the strings for Saints as they started to play the game entirely on the front foot.
The Dragons couldn't get out and once the ball reached the Saints forwards, there was no escape as Ribbans wrote his name on the scoresheet.
Grayson converted with aplomb before the Dragons finally started to ask some second-half questions.
They continually knocked loudly on the door after going to the corner but Saints' defence stood tall, rebuffing attack after attack before eventually winning a penalty to relieve the pressure.
And Saints were soon back on the attack with Fish profiting from the power of his team's pack to score twice more before the end.
Grayson added both conversions to maintain his perfect night from the tee and give the scoreline an extremely comfortable look.
Dragons: J Williams, Goodchild, Warren, Dixon (c), Gasson, Lewis, R Williams, Bevington, Hibbard, Harris; Screech, Landman; Wainwright, Cudd, Evans.
Replacements Ellis, Lawrence, Fairbrother, Nansen, Taylor, Benjamin, Davies, Botica, Loots, Morgan, Howells, Talbot-Davies.
Saints: Collins (Emery 40); Sleightholme (Worley 40), Dingwall (Hutchinson 24 (Pisi 68)), Francis (c) (Strachan 40), Pisi (Tuitavake 40); Biggar (Grayson 40), Reinach; van Wyk (Davis 20), Haywood (Gray 20), Painter; Ratuniyarawa, Craig (Ribbans 5 (Ratuniyarawa 68)); Haskell, Ludlam, Ryan, (Onojaife 20).
Referee: Adam Jones