I have a 6in Acanthurus Dussumeiri in a 75g 4ft tank. It's a really nice fish with a great personnality. I first got it when it was 2in and ugraded the tank twice so it could thrive and grow in a not so bad place... of course it ain't the sea but well, that's the best I can provide for now. It seems to be ''happy'', but as I don't speak ''fish'' I can't really say!