Overall it's a bit of a trickier ship. I'm actually not for it being one of the beginner ships due to the single front mounted gun. Often they'll stick a hwacha or flak on it, and only use that gun without making use of the side guns.
Personally I find the side guns very important, the game promotes weapon synergy. Using different damage types (such as piercing/explosive) is always more effective than a single damage type alone. For instance just using a hwacha will never kill an enemy. Most of the damage will be soaked up in the armor and components, and then it's a long reload while they fix everything. You can keep them more or less disabled, but it's going to be a slow match.
So using a side weapon (such as a gatling gun) before unleashing your hwacha or even flak cannon can massively improve performance.
Longitudinal Speed: 40.11 m/s (Squid is at 47 m/s, pyra is at 32 m/s)
Longitudinal Acceleration: 3.5 m/s2 (squid is at 5.5, junker is at 4.3, mobula is 4.25, spire is at 3)
Turn Speed: 13.99 degrees/s (squid is 18.95, junker is 16.18, mobula is 14.02, spire is 11.99 )
Turn Acceleration: 7.99 degress/s2 (squid is 20, junker is 15.24, spire is 15.02, pyra is 6.25)
Mass: 150 tonnes (Galleon is 320, pyra is 200, spire is 150, junker is 125)
Lift force: 487500 Newtons (Mobula is 900k, Galleon is 720k, Spire is 562.5k, Pyra is 550k, Squid is 460k)
Vertical Speed: 16.99 m/s (Junker is 17.06, Galleon is 17.01, Mobula is 17.01, Squid is 17, Spire is 17, Pyra is 16.97)
Vertical Acceleration: 3.25 m/s2 (Mobula is 7.5, Squid is 4, Spire is 3.75, Junker is 3)
Armor: 400 (Squid is 230, Spire is 400, Mobula is 600)
Health: 1100 (Galleon is 1400, Squid is 850, Spire is 750)
I usually like to consider the goldfish to be nimble, but that's not really the case. It's about average all around according to it's stats. The second fastest ship but not the best at accelerating, turning, changing altitude. Armor and HP it's pretty similar to the squid, just tougher (low armor, high HP). It's a good ramming ship, but only because that front gun will soak up most of the impact before the ship starts taking damage.
It can certainly be used well, but it does lack the killing power most other ships have due to the gun placements. Some of the heavy guns are difficult to use on it, because they're not designed to be used alone. You could stick a lumberjack on it, but if your goal is to snipe, you might as well use a galleon or spire.
You could try a flak, but it's going to take a day and a half to get their armor down before you start doing real damage (again, try a galleon or spire).
A hwacha is a good choice, since you can get up close and personal, and make good use of those side guns during the long reload. A galleon has a more difficult time chasing, but can often kill a lot faster with it's other weapons combined with a hwacha, where a spire can wreck with all it's light guns and a hwacha, but usually doesn't want to be that close.
A carronade is (in my opinion) one of the best guns for the goldfish. Since it's front mounted, it's a lot easy to chase and keep on them, where on a bulky galleon they're a bit harder to follow (but then again, most ships disintegrate when they're in carronade range of the galleon). And again, spires tend not to want to be that close. The average maneuverability and durability of the goldfish allow it to take the punches while it closes the distance and keep hitting while it stays on them. The single front gun and low reload time means your engineers can focus on fixing and not need to jump on guns frequently (although using a side mounted mortar, flamethrower, or even mine launcher (etc) can massively decrease the time to kill).
------------
What would I change if anything?
I think it'd be nice for the ship to be a little more maneuverable. Having more HP is nice, but it's not going to help when you can't avoid the damage and your armor is constantly popping. It only has 3 guns, two of which can be used at most, and only one being used most of the time. The components are pretty spread out, making it hard on your engineers, even though they're not as busy shooting (which can be a problem if you need them to get to the gun fast. It's a bigger ship than it seems.)