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Old 04-11-2015, 12:18 PM   #1
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I've got a question about rain and cory spawning...

I've read repeatedly about corys spawning after rains because of "cooler water". I was wondering if there is official evidence of that?, such as have people actually compared spawning rates with doing water changes with cooler water versus water the same temperature?

The reason I ask is because so many posts are saying the cooler water tricks the cats into thinking it's the rainy season and the "cool" rain water runoff triggers the fish to spawn. I'm wondering if this has been proven, or is just theory from people who associate rain with cooler water? From my 14 years of living in the tropics, the warmer it gets, the more it rains, and the rain comes down warm, unlike in temperate zones. There may be some evaporative cooling going on as it falls, but it's coming down warmer than temperatures can be in cooler seasons, and once it hits ground it's certainly hitting warmer ground than in cooler seasons.

Years ago I had a friend that was pretty successful with breeding cory cats and he said he would just ignore their tanks for a while, then start pumping up the water changes when he felt he wanted to deal with fry... he never mentioned cooler water, but I don't know for sure what he was doing in those regards.

Could it be that fresh, well oxygenated water is cleansing the waters they live in and that triggers spawning? I'm just wondering if the cool water theory is perpetuated conjecture or if people have really compared water changes with cooler water versus with water of the same temperature. A quick google search has gotten me nowhere with it.

Just curious.

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Old 04-11-2015, 12:27 PM   #2
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I don't know why, but in the wild they spawn after a good rain, so as soon as you're ready to deal with cory fry, do a large water change (30-50% maybe), And use cold water.
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Old 04-11-2015, 01:00 PM   #3
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And use cold water.

That's the "why" I am wondering about? Where I lived, if it hit 89-92 in the afternoon, you'd have nearly 89-92 degree rain hitting the ground shortly thereafter. Maybe it's different where corys are native to?
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Old 04-11-2015, 03:45 PM   #4
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Corydoras are native to South American rivers marshes and swamps so I'd guess it wouldn't get too hot there but I'm no expert on South American weather


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Old 04-11-2015, 05:21 PM   #5
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The rainy season in South America is the spawning season for most if not all fish. All of the waters swell and flood the rainforest providing all of the space and food spawning fish could ever need. If you google breeding corydoras, you'll find multitudes of articles/threads and if you were to read them all, you would find they all have 1 thing in common. They all do water changes with cool water using various methods to simulate the rainy season. I've even heard of some dedicated breeders keeping only 6" of water in the tank, adding fresh cool water everyday to induce spawning.

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Old 04-11-2015, 05:28 PM   #6
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That's the "why" I am wondering about? Where I lived, if it hit 89-92 in the afternoon, you'd have nearly 89-92 degree rain hitting the ground shortly thereafter. Maybe it's different where corys are native to?
Rain will always be a good deal cooler than the air temperature. I've been out on hot days when a storm blew in and that rain was always cold.

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Old 04-11-2015, 06:55 PM   #7
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Rain will always be a good deal cooler than the air temperature. I've been out on hot days when a storm blew in and that rain was always cold.

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I know there is evaporative cooling involved, but my guess is you hit it on the spot earlier when you mentioned space/food/nutrient brought on by rains. If it were all temperature, why aren't breeders just bumping their heaters down a couple degrees to induce spawning?


I've been in some pretty warm and muggy rain in the tropics. Granted if it's taking swamps with temps in the 90s down a few degrees I'd get it.
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