Hi peasants
Your spot on, grading is important but grading by size isnt the only thing to take into consideration. Ill explain..
Firstly a couple of points to keep in mind.. yabbie growth rates rely heavily on temp, 20-28deg being optimal and below 16deg and they enter a state of reduced metobolic activity, basically hibernation. Obviously aeration at higher temps will improve DO levels and water quality.
Also make sure your PH levels dont become to acidic, this will soften the exoskeleton and promote disease therefore reducing activity. Try keep it above 7 - 7.5.
Although nutritional requirements of yabbies is relatively unknown, I like to stick to high protein diets like aquaculture pellets, potatoe and lupins. A few worms and snails now and then are also a good addition. Just keep an eye on left over food as you would already know. I think farmers feed at around 3% per body wieght per day but I wouldnt fuss on that number for what you are doing.
Ok, in relation to grading, there are a few ways to go about it. I wont go into them all but the system I use is relatively simple. For this you require 3 tanks. A juvenile tank, a breeding tank and a grow out tank.
The juvenile tank is the most important. It will be home to the babies and berried females. Females are removed about 2-3 weeks after brood. This needs a complex habitat, I use lots of hides with pipe cut offs (its a good idea to close one end) and a massive bunched up length of shade cloth.
The breeding tank is home to 1 male per 3 females at a stock density of around 8-12 yabbies per 1m2 of floor space. Once again, hides are crucial. There will be carnage in this tank, its impossible to avoid. Move the males to the grow out tank regularly and eat the females after a couple of broods and replenish with young from the juvenile tank. Young females are good to go at around 20-30g.
The grow out tank is all male occupied, I stock this at around 30 per 1m2 of floor space. Also a haven for carnage but thats the way it goes... usually when they mault. Yabbies will grow faster in an all male situation and in fact research into mono-sexing and hybrid species is likely to intensify and increase production substantially over the next decade within the farming world.
Ive read some really good articles by an australian marine biologist Dr Craig Lawrence who bred a Cherax albidus with a Cherax rotundus which produced only male offspring, quite possibly might become the future of aussie yabbie farming.
More than what you asked for sorry but I hope this helps.
Backyard Farming Forum
