aquaculture management

[Richard on Maui]

So, I have this pond that has a lot of golden tilapia in it, none of them very big. Seems like the limiting factor in their growth is mostly food (I haven't been feeding them anything because I thought they were goldfish), but perhaps also space. It is actually a pretty big little pond, say 50 feet long, by 25 feet wide, by three feet deep at the deepest when it is full. At a guess, there are about 400 fingerling size fish in there, the biggest ones are perhaps 6 inches long. None have really gotten much bigger than this in the two years I've been here.
Do you think I need to thin them out about to get them to grow to table size, or should I just start feeding them up and see how big they'll get?
There is a pretty good biological system going on in the pond. I haven't don any measurements, but I would say there is lots of phytoplankton, there is salvinia growing on top, and various weeds like wedelia and different typoes of grass hanging down over the edges into the water. So, there is some food supply for them already. I figure I'll throw them worms out of the worm farm, and leftover scraps from the table. Maybe set up a solar lantern to attract bugs to fall on the surface. Any other ideas?

[Cornonthecob]

That's a fair bit of water....surely 400 fish would fit into that quite easily?

Earthbound obviously is the guy to ask, but from the little I know, I'd start feeding them and see how they go...if you need to thin them out you can do that later, but from the measurements you've given Richard they should have plently of water.

[christopher]

Richard,

Sounds like exciting times to me! Onya for getting it all together so quickly!

I would try feeding the fish, and if it doesn't work out, thin out the population a bit....

What a nice pump!

C

[Richard on Maui]

Yeah, the pump is awesome. I just came home from my first meeting with a newly started group, the Maui Permaculture Network, and checked to see how much water the little pond had recieved today, and it is probably at least a thousand gallons. A lot of the fish were clustered around the area where the water is flowing in, so they are obviously a little starved for oxygen.
I'll take your advice and start feeding them and see what happens.
Joel, are you around? What do you feed your fish?
I do have a bunch of the plastic 50 gallon barrels around the place, catching water from various roof surfaces. I have thought about taking some of the tilapia out, and distributing them around in these barrels, and seeing if they grow faster in there, with less competition. The only aeration they would get would be from water coming in from the gutters, and I would have to feed them I guess, and make sure not to draw too much water out of them. Now that I have my main irrigation scheme sorted though, I will be relying on the small catchments less, I suppose.
So, what do you reckon?[/i]

[earthbound]

Hey Richard, Sounds interesting all of those tilapia... I would imagine that they just aren't getting enough food to grow, you would need a fair bit of feed for 400 of them.

You have a few options for feeding them very cheaply, is the pond they are in seperate from any water course? Duckweed and azola are very fast growing floating plants that Tilapia will readily eat, and duckweed contains up to 40% protein when dried out.

An easy method of growing duck weed is to use a small pond or 50 gallon drums cut in half lengthways etc, any thing that will hold water. Add manure or compost tea, or worm juice to the water so that the water is nutrient rich, then throw in some duckweed. Duckweed can double it's volume in 24 hours when given optimum conditions... Then you just scoop out some duckweed every few days and toss it into your fish pond.
Some further duckween info here - http://www.backyardaquaponics.com/fo...er=asc&start=0

Tilapia are filter feeders and you can just add nutrients to their water, this will cause an algal bloom and the tilapia will filter the algae out of the water and consume it. This is by far the easiest method, but I wouldn't recommend it for your situation Richard because of the lack of oxygen in your pond.. Plants use oxygen 24hrs a day, during the day time they also produce oxygen, and they produce much more than they consume, but at night algae and water plants sap the oxygen out of your water and if you promoted algae growth it would only lead to less oxygen.... The way to test out whether your fish are suffereing from a lack of oxygen in the water, is to check your pond first thing in the morning this is when they will be suffering most...

If the fish aren't eating the salvinia I'd be a little woirried that they never will, and iut's just stopping oxygen transfer from the air into the water. Is the salvinia thick?

I've been working an aquaponic system that will use only duckweed and worms to feed the fish, as I'm trying to get away from the commercial feeds. Here's a pic http://www.backyardaquaponics.com/fo...opic.php?t=160

[Richard on Maui]

Thanks for the comments Joel. I will have to track down some azolla and duckweed. We had azolla in there at one time, but I think they ate it all.
We are not on any watercourses, so we can grow whatever weeds in the ponds we like, I suppose. You have got me thinking about barrels cut in half sitting on the sides of the ponds so that we can top up the supply of aquatic vegetation in the actual ponds whenever we walk past...
The fish will eat the salvinia, but it can outproduce them, when it gets going. I guess they don't call it Salvinia molesta for nothing. In fact, as with the azolla, at one time during winter when the growth is slower, the fish (and some ducks) ate it all and we had to reintroduce it. THe pond surface had become pretty much covered with it until recently, when we started harvesting a third at a time.
The oxygen levels aren't usually a problem, but we have nearly drained the pond this dry season, using the water for irrigation because we had no other choice.
Joel, do you feed worms to your fish?

[Richard on Maui]

By the way Joel, I didn't know you had aquaponics forum going. Nice one. I'll consume that one when I get a bit more time!

[earthbound]

Thats half the problem keeping the supply up when you need it, and clearing out the excess when you don't.. You can dry duckweed and store it as a feed fairly easily.. What do you do with the exccess salvinia, compost? You could probably dry that out for fish food as well, I can point you at info about drying if you like..

I've only just started feeding my fish some worms recently, though not to many of them because I'm trying to breed them up, though just today I found some news that may effect me..

I'm sure mungbeans won't mind me quoting from the post.

The reason I asked is that the most common composting worms are known as 'Red Tigers', although they are in actual fact tiger worms rather than red worms. The latin for them is 'eisenia fetida' - fetida is the latin for 'fetid'. When stressed (such as when fed to fish) they give off a horrid fetid smell that the fish find repulsive. For this reason red tiger worms don't make good fish food or bait.

The best way to check is to find one of your adult worms and look for bands (hence 'tiger') on the worm. Eisenia fetida also has a yellowish tail.

For fish food you will need either red worms (lumbricus rubellus) or blue worms (perionyx excavatus).

Bugger, and I just thought worms were worms.... :?

The forum is going great guns, don't know if it was a smart thing to start up though, it's getting hard to keep up....

[Richard on Maui]

Okay, so either I have the true blue red worms, or my tilapia aren't fussy eaters! They literally gobble up all the worms I can put in there. I recently divided my first two worm farms, into about 6 containers, so I too am in the process of breeding them up, but once I have that many bins breeding hard, I think I will be on a winner with the worms as food. I plan to try to harvest just enough that I maintain a steady population of worms, you know... Last night, I picked out a lot of fruit fly larvae and once the fish got a taste for them they didn't last long in the water either!

Yes, I am interested in your drying info. Is it as simple as laying it out on the sun on racks of some kind, or a little more complicated to preserve the protein?

We mostly use the salvinia for mulch so far, and can never get enough of it! It is such a beautiful mulch for newly planted vegetable beds in that unlike straw mulch it has a tendency to stay exactly where you put it, and you know, it is like a dirty a big sponge, so it drips water for a few days after you put it down, like an organic drip irrigation system. It does shrink a little bit as it dries out, but it goes a lovely black colour and if you put it down thickly enough it covers the bare soil well.
We've also used it as worm food, and it does compost quite well.

[earthbound]

Hey Richard.. Here's the link to duckweed drying info and some other interesting duckweed links.

http://backyardaquaponics.com/forum/viewtopic.php?t=221