Cigarette theory is a very good one. Teens do stupid destructive things to entertain themselves. I found a kid from down our street (18 years old) spitting in our pond to see if the fish would eat it. I can't even tell you how furious I was at him. Additionally I couldn't believe someone who I thought had the same love and respect for the environment would do something like that - but he did. Why? To show off to a 7-year old. At any rate, your fish were definitely poisoned. The question becomes, what kind of poison? IÂm not sure alcohol would have the concentration needed, but there are other things a person keeps in the house and in the garage that could have done it. A little bleach, toilet cleaner, lighter fluid, weed sprays etc. If there was no insecticidal/pesticidal spraying with a lot of rain to wash the chemicals into the pond (that day), then it is 100% something the kids did. Keep in mind, often the host of a party will not have control of everyone there, so he truly may not know what people poured or tossed in there. If I were you and it were my kid, I would tell him you did extensive research on-line and have determined it was something someone added at the party. If he throws a party he needs to accept responsibility for the actions of the people that attend. The ramifications of the fact he has irresponsible people attending his party, is it raises the likelihood of someone driving from his party (your house) while tipsy or drunk and then getting in an accident hurting or killing someone. Each State varies, but an incidence like that would make him (and you by proxy) liable. Teens being what they are tend to learn the hard way and maybe this is his wake-up call. Though we always wash our hands after applying mosquito spray, I highly doubt that could have been the cause unless they were spraying it straight into the pond. One again, people do stupid things when they're drunk and in crowds. My background is from the University of Michigan in Microbiology, Genetics, and Ecology. So I do know a thing or two about this :)

First of all, according to various people, you may want to reconsider keeping your catfish and pond fish together. I posted a link below - or you can do a search yourself on the subject. In our pond in Upstate NY (similar in zone to you), I remove all my tropical plants in early October. We cut back our hardy water lilies which are planted directly in the pond and drop to the bottom the other hardy plants. Our pond is 3 feet deep and approx. 3,000 gallons so the fish overwinter in the pond. I don't know what you should do with a pond that small. We purchased a plastic 100 gallon tub at Country Max for our tropical plants, and I think that would work well for your fish if you decide to bring them indoors. You would have to add a pump or air stone for aeration and something for filtration. My husband altered the "plug" with a faucet and we can drain it pretty easily with a garden hose into our basement sewer come spring. Here is a link that might be useful: catfish in a pond

If you're keeping Goldfish and their comets ie cold water fish and you practice good hygiene in your pond bringing them in for the winter at house temperature is doing them no service... Unless you have orando ect, which are sensitive to the cold.. Why not research a little... These fish are in most homes in Japan with no filters ect.. Rain and plant balance equal a happy pond... And if living in a hot climate placing a pond in a shaded spot that gets good wind is ideal... Too many people rush into putting fish in their ponds and don't understand what they are doing.. there are no filters in mother nature... Karp, Koi, Goldfish.. They are in the right pond as tough as boots.. Have only lost fish because 3 newbies got snatched by a cat.. My pond in 4/5 feet deep and 16 feet long it is beached with pebbles and stones dug out of my garden at one side to allow a planting shelf and to allow wildlife in and out... I fed my fish at the start for 1 month then I left them to eat what mother nature provides in the wild... I have an excellent overflow its a simple pipe that when it rains it flows into it... Nylons filter the waste >> I allow the levels to drop by using the water In the pond to drop 1 foot to water my veg garden in early spring and let the rain fill it up again and from water butts .. My pond is only in its 3rd year and my fish reproduced in April there are over 100 little fry... I have 3 pleos BOTTOM FEEDERS that I JUST added to control algae.. I fish out leaves and debris as I see it... And pull out any excess algae by hand... It Looks awful sterile here as we had just started the garden but this is the general size.. The sticks are to stop the dogs digging.. It has grown great this year.. Have lilies, Siberian iris, bog plants and plants that add oxygen to the water.. I think too many people complicate ponds.. Replicate what mother nature intended and you'll be grand.. I have clay pockets and caves made for my fish to hibernate strewn across the pond...

Oil slicks are usually from anaerobic conditions some place. Like when sludge or mud is anaerobic it causes the bacteria to put out waste that is harmful. They produce methane. here is a quote I found: "Because methane is a small, easily evaporated molecule, most of the methane produced by the anaerobes in their mud world escapes into the atmosphere. But some small percentage of it gets converted into larger hydrocarbons that are less likely to evaporate. They still are lighter than water, however, so they float on the surface. There is little difference between these naturally produced compounds and hydrocarbons like gasoline or oil, so the sheen on the water looks the same as if someone had spilled gas or oil." Since mosquito fish hang out at the very surface of the water I'm betting they are getting the brunt of it and direct contact. You may also be getting bacteria blooms too. Since there is no filter for the bacteria to live in. That will look like a cloud in the water. I suggest you clean out the bottom of your pond, put the lilies in a pot. Corral the water hyacinth together so you leave a little more open area for the pond to collect oxygen. And get at least some kind of water flow going. Or even just an air pump would help a lot. If not a filter at least have a water pump that pumps water from one side on the bottom through the roots of the water hyacinth. I'd really try to get some kind of waterfall action going though. A shower filter would be awesome for that. If you don't do something eventually all your fish will probably die. It will only get worse. And eventually goldfish get huge, so you'll need to do more as they grow.