Adding in freshwater prawn (aka shrimp) in a raft system

My 84-year-old father (who currently is raising about 9000 tilapia) asked me the other day what I thought about raising freshwater prawn.  We've recently started to get into aquaponics, and we've had a small 50 gallon tank with about the same sized grow bed since July 2012 (hydroton-filled, flood/drain...a very small test system). So I started wondering if it would be possible to do a trifecta-type thing and add freshwater prawn into an aquaponics system along with the fish.  (Dad's really more knowledgeable about things than I am, especially about the fish...I'm just kind of helping out on the plant side.)

At this point I have a couple of thoughts on it.  We could put them in a sump tank (as I understand it, prawn in with the tilapia would not work because they'd feed on each other), but then we'd have to take up more space and have another tank, or we could use a raft system and put the prawn under the raft.  Since we're just getting ready to set up a second small test system, I thought maybe we could try it with a raft.

I haven't researched rafts nearly as much as the media filled beds so I have some questions (that may be rather naive, but hopefully not too much).  Obviously if there are prawn under the raft, there would have to be significant DO in the grow bed.  Without the draining of the bed, could this be accomplished by just adding in bubbler stones throughout the area under the raft?  Or might there be a better way to accomplish it?

In a raft system, there wouldn't be much surface for the bacteria to grow so how do they cultivate the bacteria needed to change the fish water over to what the plants need?  Is this when other steps are needed between the fish tank and the grow bed?

Is a raft system limited in the types of plants that can be raised with it?  I've seen a lot of success stories with lettuce type plants, but not so much with other things.  We probably will not be expanding into the full-blown aquaponics filtration for all the fish he has just because of the sheer size we'd need, but we would like to work with it on a smaller scale to provide some basic vegetables for personal use.  It's more than Dad would like to do at this age, but basic gardening has always appealed to him.

Just wondered if anyone had any thoughts or experience with prawn along with a small aquaponics set up.

Tags: prawn, raft

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We looked at them.

1) They apparently don't reproduce in fresh water so we would have to keep buying juveniles.

2) They need up to 2 square feet each; which is just too much space to grow enough to make it worthwhile.

Search for "Aquaculture of Texas" if you want more info.

Thanks for the reply, David.  Yes, that's as I understand it too. They don't reproduce in fresh water so if you're doing them on a large scale, you'd either have to have a saltwater nursery or keep buying juveniles (which with shipping and such run approximate 20 cents each).  And yes, they do require a lot of space, although I believe using substrate cages as the guy on the Aquaculture of Texas site has pictured increases the number of prawn per sq foot.

If we do raise them, we're actually going to do it on two levels.  My dad will do them for profit in a large outdoor cement biofilter he already has and I'll be the one doing them for fun under the grow bed raft for our own food needs.  I've read about the prawn themselves, but what I'd like to know is more about a raft set up in connection with how I intend to have the prawn underneath.

I've confirmed that their water needs (once past the post larval stage) is the same as tilapia needs so I'm wondering if the normal raft set up would work with them or if I'll need to add extra oxygen or substrate.  I'm sure there are probably some out there who have rafts floating on their fish tanks.  That might be a similar experience to what I'm describing.

Might take a look at crawfish rather than prawns.

http://farmingcrawfish.com/

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