Backyard Aquaponics
A place to discuss aquaponics

Does anyone have experience using a grader to size fish to help with the consistency of the fish load? I'm going to be adding an additional 200 gal, sump, and will be able to include some fish in there as well. Still trying to figure out the best way to not lose a huge portions of the fish waste if my fish all reach harvest size at one time. I've heard that the grader bar is rough on the fish and rather difficult. Maybe with the smaller tanks that I have I can just draw down the water and net the larger ones, replace with some smaller ones and harvest a few plants...keeping everything close? Having a good deal of experience netting bait fish in a 50 gallon well, I don't think it will be super easy. Just wondering how you "old timers" are handling this. Thanks! -Chris

What fish species do you have, and what shape is the tank are they in?

A fish sorting device is just the absurd kind of thing I might like to invent

BW- 275 gal. ibc , and tilapia.

I guess I should have asked this the first time around, but what's a "grader bar"?

Running this stuff through what's left of my brain suggests the following...

Nature uses three grading systems that spring to mind. (there may well be many others)



The first I can think of is shallow water.

The second is aggression of the dominant beasties.

And the third is risk taking behaviour in juveniles.



Shallow water denies access to certain areas to fish that are too tall. This often means that young fish get first pick at new pastures exposed by each new rising tide. This means they get first pick at anything that has died since the last high tide. This also means that old fish DONT get first pick at newly created feed since the last high tide.

Dominant fish will often bully other fish. Bullying might lead to the bully fish being first on the scene at a new source of food. This might be a deciding factor in someone attempting to sort fish based on the particular fishes ability to be first on the scene, or to defend the scene and be boss fish.

Lastly young fish tend to be relaxed with risking their lives to gain calories. (This might manifest in humans as a mcproblem) but traditionally its an advantage to risk your life to grab a meal until you have accumulated enough that you have something to lose ("I've worked hard to get where I am') Young fish get crazy brave when a lure is run through their world, but older fish are a bit more sceptical. Its likely that the older fish are not smarter, but just that they have enough body fat that they can wait to see if the shiny hook wearing things are worth eating after all.

That's only three motivations, but no doubt there are more.

Can anyone think of any other motivations that talapia might have in their day to day activities?

From my limited understanding (haven't seen a pic or diagram) a grading bar is a sizing mechanism that can be used to capture larger fish while allowing smaller to slip through. I'm thinking like a glorified pitchfork type device that can scoop out larger fish while allowing smaller to be safe from the dinner table for a while longer. I guess my problem is that i really want to try a maximize the system and not just happy with a few fish and a balanced grow bed. I would like to 'push the envelope" and try and see how many fish as well as how many crops I can get each year.

Then you really need multiple fish tanks... and staged growth...

Yes, if I had 4-5 fish tanks, with various staged fish in each tank, that would be ideal. Since I don't, I'm wondering about the easiest, best, least stressful way of harvesting the larger fish. Hopefully, I'll be able to add additional FT and Gb as the system gets established, but this is setting me back a few $$$ now, and I need to get the initial system up, running, balanced and make sure that the larger system is a worthwhile venture.

Drain your tank down... and clove oil them..

If you can't get clove oil.. or aren't sure/confident about using it.... at least by draining down the tank...

You'll be able to better identify and net the larger fish.. minimising the stress... of just lucky dipping, and chasing all the fish around with a net...

thanks

CLOVE OIL is subject of investigation from FDA as it has not been approved and recognised safe for fish intended for human consumption!

http://www.fda.gov/downloads/AnimalVete ... 052520.pdf

Draining the tank still place the fish under stress.

Cris, how many of the big fish do you want to harvest at the time? you can just go fishing with a big hook and big bait so only the biggies will go for it!
Grading is easier when done in raceways, in a circular tank it's not the best job unless like me you just use smaller ones for production of pate' and fillet the one that are good for the vac-pak size portion.

Your right bioaqua.





This is a common method within the aquaculture industry. Why do you think it would stress them?

Yep, you're right Bioaqua... clove oil is not certified for use in Australian aquaculture either.... but Aqui-S is....

As are similar compounds in other countries...

Aqui-S is essentially (purified) clove oil by another name... it's just the company forked out the $100,000 for the certification....

While not "certified"... it has been commonly used in aquaculture for decades... and still is by many... even if quietly...

However... some concerns have ben raised regarding it's use... mostly in relation to inconsistency/impurities during manufacture....

And yes draining down the tank.. especially too far...and particularly if heavily stocked... can indeed cause some stress...

It's still a hell of a lot less stressful to the fish... than chasing them around a tank blindly... with a net...

P.S... there are also just as many concerns about similar "anaesthetic" compounds used in aquaculture... even those "approved"... such as Benzocaine...

Or indeed many of the chemicals used for disease treatments.... that's why even when approved... there are with-holding periods specified....

Does this imply that you tend to generally harvest an entire tank at a time Bioaqua...

I use separate culture tanks but you can layer two net mesh sizes in the bottom of a tank for easy grading. Smaller mesh at bottom, large mesh to catch harvestable fish on top. Lift top net up, large fish are caught in it, small fish swim through. Grading on a large scale can throw fish off feed and lead to some mortality... I prefer a batch harvest to purging tank, then to consumer.