Fish Density

[Matt Trevatt]

I remember reading that fish density is around 50kg per 1000 ltrs? Is this correct or have I not recalled this correctly?

[Murray]

The number you mention is a good starting point. I have always worked on number of fish per 10 ltrs. It's a hot topic, stocking densities
I aim to stock at 1 fingerling per 10 ltrs of water.
In actual fact I carry more than that in my main tank. I need more tanks soon for my Murray cod as they grow. At the moment I have 250 in a 1000 ltr tank, but they are still very small. My plan is to continue to grade them as they grow and have them at a density of around 50 to 60 kg per 1000 ltrs.
I have found that kind of density to be very manageable with my silver perch.

Most fish species do not all grow at the same rate. Anticipate that all of your fingerlings will eventually be at 1 kg, but you will be taking bigger ones out for consumption while others will still only be half that size.

The rate you choose to aim for is dependant on how closely you plan to manage your system, and what lengths you are prepared to go to to with your equipment.

Some commercial growers push densities well above 200 kg per 1000 ltrs, but they are on watch 24 hours and inject pure oxygen into the water and have very sophisticated filtration systems

[craigb]

Hi Murray,

I wonder if with Murray Cod they need more room to move to grow quicker?
From what I know of them they are not a real schooling fish and it might be worthwhile putting a few of them into a tank on their own to see if they grow quicker.

[nick]

i think with the murray cod they behave a lot like the barra in that they are sedentary mostly and move very fast to feed. before sitting still again to wait for the next meal.

Also the murrays are kept at high density as they have a tenancy to become territorial and like chickens if you keep a lot in a small space they have less opportunity to develop and display the behavior.

[Murray]

I have approx 200 Murray Cod in a 250 ltr tank. They are about 75mm long each.
I will have to give them more water space soon. I notice now that the ammonia levels are rising slowly in that tank even though I have a canister style biofilter in operation continuously.
The lower tank with another 200 approx Murray Cod is 1000 ltr with about 800 ltr in the tank and the ammonia levels in that tank are consistently lower.

I am keen to keep them crowded for the reasons stated by Nick, but soon I will have to get the Murrays out of the fingerling tank into a 1000 ltr tank.

Obviously, a bit further down the track I will need tanks of around 4000 ltrs in total to house the 400 plus Murrays.

I notice that the Murrays always crowd into the corners anyway, even in the bigger tank, with the exception of the odd one or two that are found stationary in various parts of the tank......but when it is feed time, they sure can move.

CraigB, I just might get 2 or 3 out into an aquarium I have just to see how they go on their own.

Oh, the Sunday afternoon BBQ's that are approaching.........

[twintragics]

as nick and murray say craig, gotta keep em crowded.

[craigb]

You guys are such a wealth of information.

Thanks.