Community Fishing Program Bulletin
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Feb 7, 2017
Veteran's Oasis Mystery Kill is Solved - Golden Alga (GA)
For close to a month we’ve experienced a slow but steady fish kill at Veteran’s Oasis Lake in Chandler. What made it particularly frustrating is that ongoing sampling by the lake consultant found no evidence of Golden Alga (GA), and our on-site sampling prior to stocking fish revealed good water quality parameters. Last week we finally were able to detect GA in samples we collected at the lake, which explains the catfish and trout that had been dying. Here’s a bit more information on GA.
Golden alga (Prymnesium parvum) is a single-celled species of algae that is found all around the world, primarily in coastal waters but it's frequently found in rivers and lakes. In Arizona, it was first discovered in 2005. As a chlorophyll-containing organism it can produce its own food like any other plant by using sunlight and nutrients, but GA can also release chemical compounds that combine with minerals in the water to produce toxins that cause fish kills in order to feed. The GA is harmless to air-breathing organisms.
When GA "blooms" (enters a phase of rapid growth & reproduction) it can produce 2 kinds of toxins that kill gill breathing organisms like fish, freshwater mussels & clams, and the gill-breathing juvenile stage of frogs and other amphibians. A GA fish kill may last for days, weeks, or months, and sometimes only a portion of a lake is affected, but the location can change from one day to the next. This is exactly what makes detection and confirmation a challenge. Blooms are more likely to occur in cold weather, and sometimes taper off as the water warms and other species of algae become more active. Treatment usually involves application of an algaecide such as copper sulfate. Unfortunately at this point there is no magic cure to remove GA from the waters it occupies. All we can do is prevent the spread to the best of our abilities.
Chill that can Kill
Cold weather can be great for trout stocking, but bad for lakes that contain tilapia. Tilapia are warm water fish that are native to Africa and they do not tolerate cold water temperatures very well, particularly those below 55 degrees. The recent cloudy weather, rains, and chilly night-time temperatures can often result in a partial fish kill. This situation occurs during normal or cold winters and generally lasts a few weeks to a month. So if you see dead tilapia in any CFP waters, the temperatures are most likely the culprit.
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