Breeding boxes if you wish to breed blackfish you will need somewhere for the female to lay her eggs this should be some sort of hollow structure 90 mil plastic tubes do fine or hollow longs that you can get from suppliers or find yourself , I made mine out of 10 mil ply  simply nailed together no glue as you can see in the photos they are not very big about 600 long and about 90×90 inside I kept them small to suit the fish I had at the time if you have larger fish you should increase the size of the hollow. I used just normal ply not form ply in order to not introduce a foreign substance to the water normal ply is stuck together with latex adhesive which occurs naturally in nature. I should add that the box above is five years old and has been exposed to all kinds of weather.

When you place the boxes in the water take time to consider the depth, it has been my experience that  as the water table warms they tend to favour deeper boxes at the start  in the early spring shallower boxes so the best policy is to have boxes at varying depths not to deep, you can see the top of my first box in the water and my deepest would be no more than 1.3 metres.