I‘m pretty happy with my Fuji apsc setup, but you‘ll be able to get a full frame body for around 500 (canon 5d mark ii, Nikon d750 or some Sony a7). Camera should have a flash sync (x-sync) of 1/250 to freeze the object.
Canon and Nikon have a ton of good lenses (a fish is about 250 euro and 50mm about 120 euro). You might need a good tele at some point, which can be more expensive.
Flashes are another topic … I use a mix of cheap yongnuo flashes and triggers, and also an old metz ct4. That’s cheap and without Metz brick it’s pretty portable.