Backyard Aquaponics
A place to discuss aquaponics

Hi there, my name is Phoenix and I'm a 17 year old high school senior. I'm currently participating in an environmental and energy science program with 5 other students, and a major part of this project is maintaining an aquaponics system!

I'm completely new to the concept of aquaponics, so a lot of what we're doing is trial and error. There have been a lot of instances already this school year where we could use some advice from someone more experienced and struggled to find that, so here I am!

We have two systems with six tanks each; currently only one tank in each system has fish, but all but one of them have plants (the one that doesn't will eventually, we were just having some trouble with getting the water to drain from the plant bed into the tank itself). Our plants currently include okra, various kinds of peppers, spinach, tomatoes, bok choy, and snap peas. The fish we use are tilapia of assorted varieties. We also just received a shipment of 500 fingerlings, 250 blues and 250 whites, which are being housed in a separate tank with an independent water cycling system.

Current struggles we're having within our system involve a lot of fish deaths. In one tank we were experiencing a death almost every day. We moved those fish from a tank in one system to a tank in the other about three days ago. Only one has died since then, but they currently don't appear to be eating anything and we're not quite sure why. Some suggestions we've found online are holding off on feed for a couple days, trying to lower their stress level, and adding salt to the tank. Clearly the salt method is out because we have plants, but we're planning on waiting till after the weekend to feed them again (it's currently Wednesday here). In the nursery tank, we've lost a lot of the new fish. We've gone from 500 to probably around 50-100, with at least 200 dying over the last weekend alone. Our water is in a safe range for everything we test for: pH, ammonia, nitrite, and nitrate. We even contacted the farm we bought from to see if they could find anything wrong with the levels we have currently that could be causing so many to die, but even they couldn't figure it out.

Any suggestions anyone might have or any pointers to other sources would be greatly appreciated!

Hi Phoenix, welcome to the forum

Sorry to hear about the fish. It would be helpful to know the size of the media beds attached to the system and any additional beds or filtration. Are the media beds or filters cycled yet?

Unless you have strawberries the amount of salt you'd need to add to help the fish with stress and to prevent nitrite poisoning (1 ppt = 1gm/L) will not have a noticeable affect on the plants. Holding off on feed and then salting to 1 ppt is with un-iodized salt (NaCl) that doesn't have anti caking agents is a good idea. Pool salt might be the least expensive way to get this if you need a lot.

It's normal after moving the fish for them to be stressed and not eat - sometimes it happens and sometimes it doesn't. It may take them a few days to get back on the feed. Not eating can also be a sign of other problems though.

Any pictures of the system would be helpful. You haven't mentioned if the fish display any odd behavior before they die or if they have any wounds or infections? Gasping at the surface, jerky movements, trying to rub their sides on the bottom (called flashing around here) are examples that you might look for.

The fingerlings might have received a shock going into your system if the water parameters were too different. It's also possible that they were exposed to high ammonia or nitrite levels during transport and you are seeing the results now. This is more likely if their water temp was high and had a high pH because ammonia converts to a more toxic form under these conditions.

Hope this helps.

Thank you so much for your help

Here are a few images of our system. The last three are of one of the big circuits of tanks, with each having six and being on the same water supply. We have two of those and they're pretty much identical but have different kinds of plants in the beds. The first three are of the nursery tank. Our tanks each have ~165gal (325 L) of water in them. The fish that we moved haven't been rubbing against the tank or hanging out at the surface much, but some of them do have some red marks that appear to be lesions, though none have more than one or two of them. One of the weirdest parts is the tank they were originally in was directly next to another tank that has a number of fish around the same age in it, so they were on the same water supply and everything, and those fish have been and are still doing great. We even tested levels from the Tank of Death (for lack of a better term) separately and they were identical to the rest of the system. Our levels have been pretty consistent for over a month; ammonia is generally around 0.25-0.5ppm and nitrite is almost at 0.

Thanks again, we really do appreciate it!

First off - That's a really nice setup

Hmm, two tanks on the same flow and one is having troubles - if they are connected in series which one came first, the good tank or the tank of death?

I think it might be a good idea to increase the aeration in the tank with problems (unless you have really tiny fish). I also noticed that in the first three pictures one tank was getting a lot more light than the others - if that's the tank of death then reducing the light level a bit (at least for now) might help the fish with stress. Neither of these is likely to cure the problem (it's probably too late for that) but might help a bit.

Do you think most of the fish that died had lesions or was it just a few of them? The lesions might be caused by disease, a parasite or just injury and they may not really be related to what's causing the fish kill. You might be able to find a useful guide online but it often requires a lab to figure this out. Based on the timing and the fact that an adjacent connected tank was unaffected, I don't think the main die off was caused by a disease.

On a side note - If you're curious about how this is done when there is a fish kill, this guide might be interesting to you and gives you a chance to see part of the field collection process used to look at fish diseases in the field - not that useful in actually identifying the disease (if that's what it is) in this case though . The samples of tissues and organs would go to a lab like the one the guide was prepared for. One part of this would be a diagnostic bacteriology lab where the tissues would be flamed on the outside to remove contamination. After this they would be cut to expose internal tissue and then tested on various media for growth and differentiation of bacteria. Other labs might look for viruses or parasites in the samples. Here's the guide - http://aquaticpath.phhp.ufl.edu/lesionguide/lesionguide.pdf

Cheers