Backyard Aquaponics
A place to discuss aquaponics

Hi guys.
Hoping someone might have some thoughts on why my channel catfish are developing a skin problem?

I noticed about 10 days ago that one of them was showing some 'damage' to its skin and the area of damage has progressive gotten larger and worse to the point the flesh was visible below the skin. Other cats are also showing similar signs of 'damage' but not all (only about 50%). The impacted fish are both male and female, and of mixed sizes.

The damage appears to be more of an abrasion than disease or parasite ( see photos)

The fish are in a 1000l IBC. They are about 10 months old, weigh between 450g and 800g. There are (were) about 13 in the tank (I removed the 4 worst with the aim of taking a closer look at them and reducing possible competition). They generally get fed about twice a day with a high protein feed. Water temp is around 27.5c, TDS is 250ppm (500us), ammonia is 0.25ppm, nitrites are <5ppm, nitrates are 0ppm, and phosphates are 10ppm (high). pH is low at 4.5 but this has been the case for many months (which is another problem I have and am not sure why it continues to be so low; I can bring it back to ~6.5 for a week but then it drops quickly).

I have two tanks side by side, and the second tank has 2month old Tilapia fingerlings and these are doing fine.

So....I am wondering if the pH and phosphates are the issue, whether there is too much competition, whether there is a disease or parasite issue. Thoughts?

Many thanks!

Ive never read of catfish attacking each other but thats not to say it couldn't happen. My money is on some kind of infection brought on be stress, and the stress in this case is the bouncing pH. You shouldn't raise your pH more than .4ppm per day.

This is also the reason your nitrites and ammonia haven't stabilised yet. A pH of 4.5 or below 6 will slow and if low enough will die off and crash the system, further adding to the fish stress.

You need to sort out your pH or your system and fish will not fair well.

Thanks Charlie. I posted a seperate question around why my pH is so low. Any ideas you have would be welcome.

This looks like ESC but without a skin scraping and bacterial lab workup it would be hard to fully diagnose. I responded to your pH question-once you have that raised back to the normal range, I would salt to 3ppt as soon as possible to avoid loss of all of your catfish. As Charlie mentioned, the pH swings and low pH have stressed the fish and made them susceptible to pathogens that naturally occur in the water.

Doesn't really look like ESC to me, looks more like aeromonas infection to me -

http://www.ag.auburn.edu/fish/mediagallery/2013/08/13/bacterial-diseases-in-warmwater-fishes-2/

Cheers

Mos def a bacterial infection (probably Aeromonas, or, since it looks like it manifests only on the upper tail section, it could be Flavobacterium columnare or Flavobacterium psychrophilum).

Unfortunately, the only 100% effective method would be to immediately remove all even slightly affected fish, move healthy ones to a temporary tank and disinfect IBC thoroughly (even then, some of the fish that looks healthy now, can easily develop symptoms later - pH swings and stress could provoke the reaction later).

You could try with sera bactopur, but removing all affected fish immediately is a must.

P.S. Do not handle those fish without gloves; do not eat them; it would be wise to burn or bury them deep.

Scotty,
Yeah you are probably right. I looked at the pics and also referred to my intro to fish health coursebook and it does more closely resemble aeromonas infection. In either case, excluding the use of antibiotics, fixing the pH issue and salting are best course of action before Humphs looses all their fish to the disease.

+1

I would also get rid of any affected fish.

I'd probably bury them deep and let nature take it's course. Both of these bacteria are able to cause problems in humans but neither of these bacteria produce spores. Your local cat may be susceptible as well so burying deep is a good idea.

It's' a good idea for anyone working in their AP system to wash up afterward and to use rubber gloves when handling diseased fish.



+1

Regarding the pH - If you haven't already fixed this what have you tried so far? Here's some information on what's going on and what some people do to cure their pH problems. It's a conglomeration of excerpts from previous posts, some mine some by others that may give you some insight -

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System water varies because everyones system uses a different source of water. For this reason, the buffering capacity of the system water varies. In most systems you want some buffering capacity which helps prevent rapid pH changes. Sometimes the source water has sufficient buffering and sometimes it doesn't. In systems that don't have enough, carbonates like CaCO3 can provide buffering. (Too much buffering though and the pH will be resistant to change. This is exactly what happens when limestone (one form of CaCO3) is used for the rocks in a system). If your pH is changing rapidly you may need to use shell grit or some other form of calcium carbonate to help buffer the pH. Make certain it is put into a sock or some other container that allows you to remove it or you may wind up with too much buffering (this isn't a one time deal, you may have to occasionally use the shell grit). If you're having to do frequent pH adjustments it's time to use the shell grit again. If the shell grit isn't bringing the pH up then you'll need to use something stronger to get the pH up before the shell grit has any affect and Potassium Hydroxide is probably the best choice for doing this.

So by improving the systems buffering you've made it so the pH changes more slowly. One of the down sides of using CaCO3 is that Calcium competes with Potassium for uptake into plants. The more Calcium there is, the less Potassium actually gets taken in. For this reason, once you have some buffering, it makes sense to raise the pH by alternating between Potassium and Calcium in some form, preferably without adding more carbonates (some have to leave the CaCO3 in others don't). Potassium hydroxide and Calcium Hydroxide are good for this but they are strong bases and caution should be used when adjusting the pH (Use these so Ca and K additions are 1 to 1 based on chemical formula).

Note - for raising pH - There are several different ways to do this - from most basic to least basic --> Hydroxides, Bicarbonates, Carbonates. Do not change the pH by more than .4 points during a single application (per Rupe).

Hydrochloric acid (HCl)(aka muriatic acid) - Add to topup water - adjust this to 6.0 to 6.5 and let stand 24 hours before adding to system. This will lower the system pH gradually over time.

Potassium Hydroxide (KOH) - Used to raise pH and add potassium. 1 T / 1000L every few weeks.

Calcium Hydroxide (Ca(OH)2) (Hydrated lime or Brickie's lime or slaked lime) - Used sparingly and with caution (caustic) to raise pH and add Calcium. Probably adding about 1 tablespoon per 1000L until you figure out what works for your system is a good start. Remember not to change the pH more than .4. Contains other things like magnesium and doesn't add carbonates.

(Mr Damage suggested using Calcium Hydroxide alternated with Potassium bicarbonate in a 3:1 ratio - this was for a low carbonate system where the pH kept dropping and they hadn't been adding carbonates).

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On the possible ways to adjust the pH - everyones system water is different so consider these to be estimates on where to start. Remember don't change the pH more than 0.4 at any one time.

Hope this helps