Did you do a water change? What is the pond temp?

When I've lost fish and they are laying on their side like that it is usually a bacterial infection so you could try some antibiotics but it also could be from lack of oxygen. Any other symptoms?

Otherwise if they are just cold and stressed the salt, warmth and oxygen should help. I think it was fine to bring him in so the temps don't fluctuate as much. Just keep him somewhere dark and quiet. You might want to bring them all in because when fish are together I find they seem to do better. You can get one of those big rubbermade totes if you need a bigger space. Keep an eye on the inside water, do small partial water changes to keep it clean. Definately common for fish after a long winter to be stressed and prone to illness. Good luck!

Parasites have been dormant in the cold temperatures and now that the water is warming they are becoming active again. It is entirely possible your fishie has one of those parasites. If it doesn't respond in a couple of days, try something for parasites in addition to the antibiotic. It might be wise to treat the whole pond.

Thanks for your kind replies. The good news is fishie is swimming upright this afternoon. I was hesitant to check him this morning (Schrodinger's fish syndrome: he's neither dead or alive until you actually look), but he was still hanging in there though still laying flat on his side. When accidentally agitated he would swim upright as yesterday.

I have yet to do any water changes, last weekend was the first time I turned the hose back on! Its on my list for this weekend. I did scoop out all the leaves that made it thru the winter netting. Main filter pump is now on, a good bubbler was on all winter. I have 2 UV pump/filters going to kill the green stuff till it's plant time, they make plenty of circulation. So... I doubt O2 is an issue.

Temps are in the mid 40's now. They have changed a lot, actually hit near 50 mid Feb as the bubbler air pump is inside a tote box and the sun warmed the box which pre-warmed the air it was pumping.

Last summer I did an aggressive Praziquantel treatment per the goldfish board's suggestion (URL below), so hopefully parasites are also a non-issue.

Now that he's doing better in warmth I'll need to set up something better until I can put him back in the pond. Its funny the work I will do to support a fish I bought 3 years ago for 27 cents!

See, I initially bought "feeder fish" to start my pond and some are still around. Some are also quite striking!

url=http://thegab.org/Illness-and-Treatment/commonly-used-medications.html

Ernie...on another post about "Adding frogs and fish to our new pond in So Calif" you posted "I get my green frogs as tadpoles for 2-3 bucks a piece from the local garden stores". I also live in Southern California and am trying to purchase some tadpoles. Can you tell me what garden stores you purchase your tadpoles at?

Here is a link that might be useful: Adding frogs & fish to our new pond in So Cal

Sorry while I do get my tadpoles at local garden centers "local" is here on long Island New York.

I have also seen some for sale in the larger fish stores.

Final fish update: Everyone pulled thru OK, I put two of the four back last month but one of them got eaten one night so I'm leaving everyone where they are for the time being. My water lettuce is still not growing explosively as it usually does and the poor things don't have the best top cover to hide under.

Not sure what critter came thru to snack on my buddy but I suspect a neighbor's cat, there are at least two who will wander our yard.