Backyard Aquaponics
A place to discuss aquaponics

After removing the tilapia from the tank they shared with the catfish, I put some rather large trout in. There are now 9 catfish and 7 trout in the tank for about a total of 20 lbs of fish. Maybe a little more. The tank is about 200 gallons. Over the last week I noticed all the fish are congregating in one corner of the tank except for the two largest trout who do not seem bothered. The hang out in the corner where the air stones are. None of the fish have eaten anything since the trout went in (two weeks ago) - they just are not interested. We have had some wild temperature swings and the tank temps have been up and down like a yoyo. A couple of the catfish have developed some fin-rot and one trout has taken to gulping air at the top of the tank.

The pH and other parameters look fine. Over the last two days I have started to add salt. I'll bring it up some more tomorrow. As of a few hours ago, I put the pump on manual and I'm just letting it run constant flood in case DO is a problem. The total weight of trout that went in probably trippled what the tilapia were. I'm guessing the fin rot is from stressing of both the new larger fish and the temp swings.

I think I have done just about all I can do except for cull back some of the fish. So the questions...

At what point is it not safe to eat a not so healthy fish with fin rot?
And could the trout have effected the DO so much that they are all suffocating?

Thanks
Mark

The trout will require higher DO levels than catfish or tilapia. That's most likely why trout are hanging out over air stones.

As long as you don't eat trout sushi the fin rot won't harm you, cook it. If you didn't have fin rot prior to trout introduction, obviously they introduced it. Can't answer your density question, seems okay to me. Ten gallons per pound seems reasonable from an aquaculture standpoint.

DJV - I think it's safe to eat the fish with the fin rot. As far as I know it's an topical infection, i.e. only affects the fish in that spot. So as long as you don't eat the fins, you should be fine.

10kg of fish in 750 litres of water is getting crowded, but not over the top, but you definitely may have low DO problems asa result. Can you add extra aeration to see if that improves things ?

You may have ammonia problems too if they do start eating as that is a big step up in biomass for your filter to suddenly have to cope with the output from.

I forgot - I do have an extra air pump. Just added another air stone in there.

It is not just the trout hanging out near the air...the catfish are right along there with the 5 smallest trout. Only the two big trout are swinging around. I also had to add some tap water yesterday (with Chloramines) as the sump was way low. Less then 10 percent though. That is about when the one trout started gulping the air.

We'll see how they are tomorrow morning. If no changes, I shoot a quick video...it is really bizzar to watch. The one trout at the top is pretty un-bothered by me also. I can get a quick pet of his head in before he dives for cover.

Adding the chloramines could have damaged their gills making it more difficult to get air.

My trout react badly to any change in water conditions, usually by jumping out.

The catfish showing signs to tattered fins is probably a sign of stress from adding the new fish. Try to keep the water quality as good as possible and keep the aeration up and hopefully they will recover, otherwise eat them before they get sick enough to die. Catfish can't take very high salt levels so don't up the salt over about 3 ppt.

My catfish are not currently eating but that is because it got cold here.

It was dark by the time I got home, so I did not get any video. I have had extra air going and running constant flood for almost 24 hours now. No change it fish behavior. I guess we are having trout and/or catfish for dinner tomorrow.

I've found that they eat far less at 3ppt (at least initially), but seem healthy even up to 6ppt for days. Perhaps I have a different strain of cats (this current batch seem to be more sensitive than my earlier trio), but sources I've seen variously give 8ppt to 12ppt as limits. Perhaps these are the 100% death concentrations.... ....and we want 0% death.

it sounds to me like there is some agro, the two trout swimming around in the middle are most likely dominating the tank and so the rest of the fish are oppressed?

I definitely agree with some of the posts that salt to 3ppt is wise (I usually add it all in one shot rather than gradually) and that the culprit may be low O2, but have you checked your nitrites and ammonia? That much added fish mass could easily overwhelm the filter and it may take a week or three to stabilize...

The fish sound like they are definitely stressed.

The only time I could pet one of my trout was when they were sick. I don't think the DO levels are to low or the larger trout wouldn't be swimming around like they are. It's possible that you got a chemical spike or a disease that caused gill damage. Upping the salts was a good call. I would also take a look for a dead fish.

I agree with Grunta - the two big fish are probably being agressive toward the others. If they are large enough to eat you might want to just cook the two bigger ones up and see if things get better. Other than this I would cover the tank and leave them be so they can de-stress.

I culled back three of the trout tonight. I did not think to weigh them until they were already cleaned. So I removed well over three pounds of fish. I only got one of the big trout though, the other one was just to fast and the catfish kept getting in the net. Will post pics to my system thread tomorrow....oh ya - they tasted fantastic!!!

Sounds good. You might have to have a go at the other big one again but taking 3+ lbs out should definitely help. I'll keep the fingers crossed for ya!

Always a good day when you get to eat the problems instead of composting them

Any updates?