Backyard Aquaponics
A place to discuss aquaponics

Help!!! I have 4 tilapia in a 350L tank with about 200l of water in it. 2 are about 250mm, 1 about 150mm and one about 75mm. I looked at them this morning and all but one small one (~75mm) had their dorsal fins shredded. There's nothing but the bones exposed. Has anyone ever seen this before? They seem ok other than that. They're swimming and eating.

Aeromonas bacteria, needs treating with salt. And cleaning the Fish tank, rincing the filter if you have one, maybe a go with H²O² for medical use at 5% of total tank volume could clean the water aswell.

Catch the fish and put them in a bucket at 20g/L of salt for 1 hour. Put the water, then the fish and put the salt quantity and wait for it to dissolve itself. Do that 3 days in a row and see. If it doesn't go after 4 days try it again.

If it doesn't work might have to go for a human generic antibiotic: trimetroprine sulfamide or oxytetracyclin.

Each of these can be diluted in the fish food and used at very low concentrations, there are no residues after a month, can wait for two in case. If needed, i'll check the dosing protocols, ask for them here and i'll post them.

Are there signs of violence?

How has your water quality been?

Do as Amaca says, but ultimately most disease can be attributed to stress. Stress usually means poor water quality (probably ammonia/nitrite, but could also be pH bouncing or temperature problems) or violence. You'll have to eliminate the root cause of stress to solve the problem permanently.

btw, if you're salting an AP system, remember that 20ppt (g/l) will toast the plants.

These fish had a terrible start. I picked them(9 of them) up on Jan 14th and hauled them in the water they came from. I thought that would be a good idea since they were living in it with no apparent problems. The first night the water got down to 50F and I lost 3 fish that night. I bought a heater and put it in and brought the temp up to 65F over about a 10 hours period. The next day 2 more were dead. I was waiting on my test kit to arrive but I drove into town and bought one. The ammonia level was 8.0!!!

I immeadiately drained the tank and put in fresh water and started checking ammonia and temp every day. After that I never let it get over 1.0 and exchanged water daily until a few days ago when my system started cycling and ammonia went to 0. This morning my readings were:
ammonia - 0
Nitrite - 1.0
Nitrates - 10
PH - 7.5

I did a 100% water exchange. that's when I saw the problem.

There does seem to be some fighting going on. Being new to fish I don't really know what to look for but for sure they seem to chase each other a lot at times. At other times they just swim together in a group.

I think it's interesting the smallest of them doesn't seem to have any damage at all....

I have no plants in my system yet. I was going to add some tomorrow to work on the nitrates.

I just noticed something else today that might mean something. Most of the time when I take the cover off that tank there is one fish hiding behind the pump....

I've heard that if the water temp drops below 53 F that the immune system of the tilapia might not recover very well if at all. The guy at Aquatic Eco systems definitely supports the idea of in ground tanks or ponds for Tilapia around here, otherwise heating is a definite must.

Of course my first thought was violence among the fish or from a predator but not knowing fish or their diseases I can't really say. You mention a cover so a predator is probably not to blame.

OK, that explains the stress source. Goodness.

Give them some hides, too. Sections of PVC big enough for them to swim inside, or flowerpots turned on their sides make great caves to hide in. And do what Amaca says.

If your ammonia or nitrate rises above 2.0, do a 20% change daily and hold off on the food.

Thanks for all the great advice. I'm on it.

Don't treat in tank but in a bucket because the dosing is a shock treatment, so the fish need to get back to their fish tank water to recover properly from the shock. But it should kill the bacteria/fungus association quite fast.
Good luck

Ok. I removed the fish from their tank, put them in the salt solution for an hour, cleaned their tank and refilled it with fresh well water. When I took them out it was obvious that these fish had been beaten up. All three of the larger ones have scales missing on several parts of their bodies.

My question is: Is it possible that the one fish with no damage is a small male beating the rest up? He's 1/3 their size...... If this is the case should I remove him for awhile?

I did put in three large pots so there are now places to hide.

if you remove the small one for a while you would know for sure if he is the cause of the problem

How long does it take for fish to show signs of healing from something like this?

Within a week I'm sure they will look better.