Tilapia dying despite good water conditions, help!

[Ng Dong Wei]

Hello fellow aquaponists:

Recently, I have experimented with a new system (i.e. grow towers above a single fish tank that houses the fish and water pumps, see a href="http://www.aquaponiclynx.com/WordPress/wp-content/uploads/2011/03/t100-1-Medium.jpg>">http://www.aquaponiclynx.com/WordPress/wp-content/uploads/2011/03/t...;) and have experienced totally mortality of all my tilapia despite maintaining key environmental factors (i.e. pH ~6.8, regular removal of solid waste, ammonia 0ppm, nitrate 80ppm, nitrite 0ppm, temperature ~22-24 °C, new system was situated in heated indoor environment). Below is the timeline of events:

1. In the new system, I cycled the water and there were no nitrites and low levels of ammonia; as well, nitrate levels were increase suggesting that the key nitrifying bacteria had become established in the bio-filter.
2. I transferred 11 fish (i.e. ~5” in length) from an old system to the new system.
3. A couple days afterwards, key environmental factors were still being maintained but the tilapia had not been eating any of the fish pellets they were fed. The tilapia continued this behaviour until their death.
4. Two months later, I discovered one of my tilapia had died. Then subsequently over a course of fifteen days 10 more fish died. Within this time, we tried to improve the situation by cleaning the tank, changing the water in the system, and reducing feeding frequency and the amount of feed. Upon inspection of the external surface of bodies there were no signs of physical trauma or pathogenic infections.

I have several possibilities, which are not necessary mutually exclusive and there is not a clear cause and effect relationship, as to why my tilapia may have died:

Psychological shock: When the tilapia were transferred to a new system, which may have caused the tilapia to lose their appetites. As a result, they starved themselves and made them more susceptible to pathogenic infections.
Environment shock: Environmental factors, other than the aforementioned water conditions which are at acceptable levels, may have caused stress, e.g. psychological shock, to the tilapia in the new tank.
Nitrate shock: Moving the tilapia from an old system with >160ppm nitrates to a new system with much lower nitrates may have stressed the tilapia. As a result, they starved themselves and made them more susceptible to bacterial and pathogenic infections.
Electrical shock: Electrical leak from electrical components in the fish tank may have “shocked” the fish so much that they became psychological and/or physiological stressed.

I know this system can work because others have purported it to be the case. If anyone has any insights on this issue and could help me, I would be very grateful. Especially any ideas on why the fish would not eat anything.

[Alex Veidel]

Well, for one thing, you're keeping your nitrate levels too high. You want 10-20ppm for nitrate, not 80.

Couple questions: how old and how big are these tilapia? Have you done any water changes, or made adjustments to pH? If you adjust your pH more than .2 (that's [point]2) a day, you can easily stress out your fish. Switching your fish from one tank to another may have caused the problem, either because of a change in pH or the change in nitrates. If your test was reading at 160ppm, it may have been much higher than that, since that's the end of the scale for some tests.

[Harold Sukhbir]

Hi Ng,

Please describe the process you used for introducing the fish to the new system. Also the lowest temp range is around 22 C, which will slow/stop their feeding and is not an overall good temp for healthy growth.

[Ng Dong Wei]

I would make the conditions in the new system similar to my old system (e.g. pH, oxygenation similar etcetera) and then I would directly transfer the tilapia from the old system into the new system. When I have had done so in the past, i.e. old system to a new system of similar design, the tilapia would be very shy and not eat and stay near the bottom of the tank. But after a couple days they would begin to act like normal fish; e.g.eat, swim, . For some reason, it was different this time.

I should probably add that my old system was a deep water culture and media bed hybrid.

Harold Sukhbir said:

Hi Ng,

Please describe the process you used for introducing the fish to the new system. Also the lowest temp range is around 22 C, which will slow/stop their feeding and is not an overall good temp for healthy growth.

[Harold Sukhbir]

Hi Ng,

The Ph and temperature are the main conditions affecting the transfer. Usually the fish are left in a container(plastic bag) with small holes for about 1 hour to slowly acclimatize to the new conditions. This process is to minimize the "transfer shock" to the fish. Fish which experience this shock usually do no have longevity. They are also affected if they are stressed by the harvesting procedure. Transferring is a delicate process as fish are extremely sensitive creatures.

[Alex Veidel]

Haven't heard about putting small holes in the bag...I like it :) I've usually just added a little bit of water to the bag from time to time.

Harold Sukhbir said:

Hi Ng,

The Ph and temperature are the main conditions affecting the transfer. Usually the fish are left in a container(plastic bag) with small holes for about 1 hour to slowly acclimatize to the new conditions. This process is to minimize the "transfer shock" to the fish. Fish which experience this shock usually do no have longevity. They are also affected if they are stressed by the harvesting procedure. Transferring is a delicate process as fish are extremely sensitive creatures.

[Ng Dong Wei]

Thanks for your help, Alex Veidel and Harold Sukhbir. I'll continue to seek what other information is available.

[Jeff S]

I moved my adult fish 1-2 months ago. They seemed to become shy and hid bunched up in corners for a while and didn't appear to be eating. They are eating now but not while I'm looking. When I close the lid on the tank they will eat.

[Steve R]

what is your KH?

[Ng Dong Wei]

I attempted the system a second time for a shorter time and I am starting to suspect it's a copper problem because there is a brass plug in my system.

[Steve R]

brass is a no no

[daniel van niekerk]

i am trying to breed with my tilapia,i split them up due to fighting and now they are hiding away and not eating as they used to is this supposed to occur when breeding?

daniel

[Jeff S]

Daniel, could be either / or. Male Tilapia are aggressive sometimes when on the make. Females will aggressively guard an area of the tank and not eat when she is brooding. Also fish will sometimes stop eating for a while when you move them so you'll just have to watch for additional signs. Your first breeding experience is always frustrating.