He is actually still probably right.

If we say the fish is 2cm wide and 7.5cm long (average length according to wiki) That's 23cm^3 Assume the fish is neutrally bouyant so it's 1g/cm^3(I know deep sea pressures change density, but let's just go with this)

1 quadrillion*23g= 23 trillion kg

So like... 1/32 of that is still around 100x bigger than the trees.

Fine, you want a species? Cyclothone alba, circumglobal, possibly in the high trillions [0].

[0] https://researcharchive.calacademy.org/research/ichthyology/...