Volume of the fish pool

= 2000 cm x 600 cm x 150 cm

= 180 000 000 cm³

Volume of water

= 110 litres

= 110 000 cm³

Volume of water and fish

= 0.75 x 180 000 000 cm³

= 135 000 000 cm³

Volume of water and fish at first

= 135 000 000 cm³ – 110 000 cm³

= 134 890 000 cm³

=134 890 litres