Backyard Aquaponics
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Several lakeside towns in the Philippines are struggling to cope with mountains of rotting fish that were killed by a sudden drop in water temperatures at the weekend.

The Bureau of Fisheries and Aquatic Resources says more than 750 tonnes of fish have died since Friday in Taal Lake near Manila, hitting several towns whose economies are heavily reliant on the fishing industry.

Scientists say the onset of the rainy season led to a sharp drop in water temperatures that depleted oxygen levels in the lake.

Most of those killed were milk fish and tilapia being commercially bred in cages along the lake's shores.

"There are just so many dead fish," said Zenaida Mendoza, mayor of Talisay, one of the worst affected towns.



"Fishermen are hauling them manually using their boats and bringing them ashore. But the rotting smell is overpowering and could pose a health risk."

Ms Mendoza says sanitation and health officials are working flat out to dispose of the dead fish, although many remain exposed to the open air due to a lack of suitable sites to bury the hundreds of tonnes of carcasses.

Volcanologists say the incident is not related to recent activity of Taal Volcano, which lies in the middle of the lake and has been rumbling for over a month.

- AFP

http://www.abc.net.au/news/stories/2011 ... 230806.htm

How can a drop in temperature cause a drop in O2?

An inversion?

It may just have been the drop in temperature ....

I think obo has it right. In the Spring and Fall lakes turnover. With a heavy rain and/or rapid temperature change you can accelerate the turnover of a lake and cause a fish kill. The water at the bottom is oxygen depleted and may have other quality problems as well so that when it comes to the top there is a fish kill.

Yeah CD could just be the temp.

I thought I read that it wasn't a drop in temp but an increase in temp - due to active volcanoes somewhere. Either way, same result.

Yeah, needless to say I didn't read all the way to the end of that article before I posted....

Tip them into the volcano

I wonder if they have improved their fish rearing practices since they had a fish kill in 2008. Here is an excerpt from this site - http://www.gmanews.tv/story/125957/BFAR-warns-of-fish-kill-in-Taal-Lake

Every one is wanting to overstock, it's not just here on the forum......

These guys never learn though - check out this studies conclusions - http://philminaq.eu/pdf/Modelling%20and%20Monitoring%20Workshop/Taal_final_report_web.pdf

The conclusions at the bottom of page 26 tell the story. You can also see that overfeeding is a real problem and that rainfall is connected to fishkills (particularly the first flush of the year). Interesting as well that there is much higher organic content in the sediment near the pens (I'm sure because of the overfeeding). This sounds like a really bad way to do aquaculture.

More confirmation that over-stocking was the main problem...

http://www.thefishsite.com/fishnews/14951/government-to-assist-lake-taal-farmers