Backyard Aquaponics
A place to discuss aquaponics

Cheers Seamonkey, used to the pump running continuously.

So I thought I'd see were my flow in my Trout tank sits in comparison to PLJ quote just as an experiment



My tank is 2.63m in diameter so I timed a floating milk bottle lid to see how long it took to do a revolution . It was measured 100mm in from the edge of the tank so 2.4m x 3.14 = 7.536m. It took 70sec for 1 rev, so 7.5m/70sec = 0.107m/sec of water velocity

For the above quoted velocities I used a 300mm fish for my experiment. 0.5-1.5 equates 150mm and 450mm which is 0.15m/sec and 0.45m/sec

All I can say is I pity the poor fish that have to swim at 0.45m/sec continuously.

In comparison my Silver perch tank (same size) took 120sec/rev = 0.0625m/sec

Before I started this little experiment I actually thought I had heaps of flow for the trout. Not that I plan on changing anything. But its interesting to see where I sit with in those spec's.

This is what it looked like with last years fish, it gives you an idea of my water velocity



Muzza

Muz1970, I may have remembered the flow rate figures incorrectly but they are thereabouts. The article also stated that flow rates at the surface and at the bottom of a raceway are less than the central flow due to friction/surface tension etc, and the fish could alternate between these zones.

I think it is great that you conducted your experiment. Perhaps you could repeat it with an object in suspension rather than floating on the surface since I think that would give you a truer water speed figure.

I remember Ryan posting something about keeping an even flow rate through the fish tank. Ill have to revisit his thread to find it again.

PLJ, I'll give it a go when I get back from work. I imagine it to be a bit tricky getting something to stay half way in the water column. It will be interesting to see the comparison.

Hiya Muz, how about half filling the bottle with water? Keen to see the results.
That looks like quite some water speed in yr tank, is it like that all the time?

Hey Skeggley, I'll give it a go mate, and yes that's my normal constant water flow through my Trout tank

Muzza

I have reduced the amount of feed my trout get each day on the basis of your advice, and also because my FT nitrites were spiking at the previous rate of 2% of body weight. The latter issue pertains to my filtration, though, not so much to what the fish can process.

A fish of 100-200g may only need to be fed 1% of its body weight per day, Troutman, but do you limit your 100-200g trout to that amount of food?

I have modeled this scenario and I cannot see how it is possible for my fish to achieve this size in the time available, based on the feeding rates stated above. Even if fed at a full 10% of their body weight from the time I received the fingerlings through until they reached 100g, and then at 1% thereafter, the earliest my fish could achieve a weight of 450g would be 29 Sep. (Your fish achieved this weight by late June!) My calculation generously allows for a starting weight of 50g, which is most unlikely since, by my reckoning, the fingerlings were in the 4-5 inch fork length range when received on 8 May, which equates to 40-65 fish/kg or 15-25g each. (http://books.google.com.au/books?id=4w9 ... th&f=false) The grow out time for 450g fish is an additional 2 1/2 weeks from a starting size of 15g.

I would really like to grow my trout bigger, faster but I can't see how it can be achieved using your advised feed rates. Someone please let me know where my logic or my arithmetic has failed.

My system seems settled on a feed rate of 0.8-0.9% of mean trout body weight*, which for today works out to a 500g. I add an increment each day as they grow, currently 6g/day, so tomorrow they will receive 506g, and so on. The fish clearly want more feed but I have to be cruel to be kind since, each time I have bumped up their feed past a critical point, the system has 'hit the wall' and I have lost a couple. I can throw the fish 250g of 7mm pellets and the lot will be gone in 3 seconds of thrashing and splashing. This is a long way from feeding them all they can eat in 5 minutes!



* Assumes a 1:1 feed conversion rate and that the mean weight of trout, as calculated by weighing three fish last month, is close enough to be useable.