Backyard Aquaponics
A place to discuss aquaponics

I've been growing 15 Silver Perch fingerlings in an IBC for about 4 months now. They are very shy and stay down at the bottom of the tank. It is quite dark in the tank and the fish hide under the pump filter. When I put in feed they only ever eat when it sinks to the bottom and I only occasionally see glimpses of fish as they dart out and around at the bottom. Up until now I didn't really have a good idea of how many fish are left.

Yesterday I removed the pump and due to the current light conditions (and possibly changes in water clarity) I was able to see much more clearly and, with nowhere for them to hide, could observe close to 15 fish (still hard to tell exactly). What I noticed were that 2 were more than twice the length (probably 5 times the weight) of the others! The biggest were approaching 6-7cm long while the smallest were still about 3cm. I also noticed when I put in feed they all schooled together to eat out in the middle of the tank. This never happened when they had somewhere to hide when I'd only ever see a few dart out at a time. From this I am assuming that the bravest are eating the most.

My pump is at the bottom and I could lift it up higher to remove the hiding place. Do you think this is worth doing or should I just let them continue to grow at very different rates? Will the big ones get so big they decide to eat the little ones? It will actually be quite practical if they do get to full size at different times. Does anyone have any thoughts?

Their varying growth rates is one of the reasons many people like SP's, it allows for progressive and ongoing harvesting once the first few have reached plate size. From that point onwards you simply replace the harvested fish with the same amount of fingerlings. Myself, I would prefer to start with larger fingerlings, in the 6-7cm+ range, even in a new system, but especially if you are adding them to a system with larger fish already present, that way they have half a chance of getting a feed.

Being in Melbourne, you would want to try and get as much size on the 3cm ones before your water cools down too much. That's another reason for starting with larger fingerlings. In dams or large tanks where they are bred, which have large water volumes that hold heat better or have a more stable temperature, the small ones may be alright over winter, but in a small backyard system with a smaller water volume that is more susceptible to temp changes, those small ones may struggle to get through winter.