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Over the years, the discussion frequently returns to the issue of the life expectancy of goldfish, and many of us would quickly rattle off that goldfish can live 10-20 years. Armed with this sort of number, many goldfish keepers, including myself, in turn expect the goldfish in our keeping to live that long, if not longer. Recently, I've become very suspicious of this often quoted number, and set out to try to see what scientists and ichthyologists might have to say about this. Here's what I found. I selected only two sources to present here. One is from the US Geological Survey, and the other is a recent journal article on goldfish in the wild. Here are the links: US Geological Survey http://nas.er.usgs.g...x?SpeciesID=508 This one has tons of references, so that you read more if you are interested. Recent paper, titled Population Status of Gold Fish Carassius auratus in Restored East Hammar Marsh, Southern Iraq http://www.kau.edu.s...57307_27538.pdf I'm not going to go through all the points of both of these sources, but I will sum up some of the more salient observations, as described. 1. The life expectancy of goldfish was found to be 6-7 years. What this means is that while a certain number of goldfish can live much longer beyond 6-7 years, it's not realistic to expect 10-20 years for all of them. When it comes to certain fancy goldfish types (more round bodied), the average lifespan may be even lower. 2. In the wild, the goldfish diet is composed of 60% brown algae, 20% green algae, 15% zooplankton, and 5% cyanobacteria. This means that MOST of the food that goldfish eat are plant based. You can probably now see why commercial foods can sometimes be so problematic for goldfish. 3. In the wild, the biggest population of goldfish caught are 3-4 years old. My interpretation of this is that the goldfish are in their prime at this age, and go into decline after this. What does all this mean? Well, first off, it's unrealistic to expect our fish to live 10+ years. It's an amazing bonus when this happens, but the average is 6-7, and less for fancies. Secondly, if you buy goldfish that are already 3-4 years old, that's already half their life expectancy. There's a nice chart of length versus age in the article (for single tails). Finally, most commercial foods are really not in line with what they would eat in the wild. None of this is really a surprise, but I thought I would share the links with you.