Average ages for wild animals are not so easy to calculate. Their record keeping is too sloppy.
The problem has to do with the sample size they use to make an assessment and how much it may or may not be representative of the species. It also matter when and how they make the assessment. Fish in the wild are subject to changing conditions. Some improve things foe them while other do the reverse. And this especially needs to consider the human role in it all.
For example consider fish from the river of Brazil which run through areas where the poorest people are living. For many years ome of the survived by mining gold. "
Contamination Risks: Mining releases arsenic through solid tailings, liquid effluents, and gaseous emissions, contaminating air, water, and soil." Big companys are regulated and must do what it takes to handle the potential arsenic. Poor subsistence miner cannot and do not do this. So their activities contaminate the local rivers. But they needed to make a living anyway they could.
However, when they were taught about the ornamental fish industry and the money it involved many switched what they did. Then they behan protecting the rivers rather than harming them. And then things change, Brazil stopped allowing the export of any fish and replaced that with the permitted list of the plants and animals allowed to be exported. This meant fewer fish were to leave the country. An they there is all the damming of the rivers. These push the native people off their land, and they often have negative effects in fish populations including those which are permitted for export. Some some of the people have gone back to mining gold.
So if researcher samples the population of a species which lives in a river after it has been dammed and/or effected by arsenic. this must effect the lifespan of the fish they are investigating. And the reverse would be happening if they did the research when a the river was being effected and then the mining halted. It wshiould be a reasonable assumption that this would effect the coming generation fo those fish.
And this only cover wild fish in the wild, What about fish in our tanks? Consider 1,000 fish come into the country from the wild or fromma fish farm. Some number of these fish will have physiological problem which do not effect behavior or appearance. A dish is born with a bad heart and the older and bigger it grows the more likely it becomes it will have a massive fatal heart attack, So siome number of 1,000 or born doomed to have a less than average lifespan whatever that average might be. An then we can assume dome number of the fish will sufferer injured in transit we do not see either.
Now the fish from the 1,000 that do not die at the importer will find there way to other places. Most will go to wholesalers if private vendors who can buy from the importer or transshipper. And from there the fish will eventually end up in our tanks. No matter how healthy a fish appears when wen acquire it, we have no clue if it has a bad heart ir is healthy as a horse and will life a longer than average life?
And then like GaryE said, when fish dies in our tanks, how do we know it wasn't our fault? There is little way to know since we cannot rule out heart attack, stroke, a mutation we cannot see etc. We can know were forgot to add the declor or we have the wronf parameters etc.
All I can tell you about mu fish is how long I have had them. I lost a 6 inch clown ;loach about 3 or 4 years after I got it. I have one of the other that came with it in a group of 4 which is a foot long, healthy and about 25 years old. I got 4 in 2003 at about 4 inches. I actually froze the one which died and sent it to someone to do an autopsy who told me to freeze it. When he took it apart and checked it out he could find nothing obvious that caused death. He suggested it very well could have been a heart attack or stroke. But everything he was able to examine looked as it shpoul. No he was not a vet etc. He was an expert fish person who was able to make the invesigation of the sort he did and to be able to spot things that did not need in depth lab grade investigations.
I have had zebra plecos die in my tanks and also have some I know are still alive and must be at approaching 25 years old. I got it in Apr. 2006 as one of a colony of proven breeding fish. That was 19 years ago. It had to be 4 or 5 years old at the time. They are in the tank of another member here who was willing to provide them with an "old fish's home." I had my final two offspring and since that was the last of them, I sent them along as well.
IMO. one of the neat things about zebras is that they jide a whole lot. This is especially true if you do not crowd/overcrowd them without providing a ton of cover for them. When we do this, because they hide so much, spotting a tail or fin, let alone a whole fish, it a real treat and always makes one smile. Plus their fry are really cute. But I have no clue how long any specific one of them is going to live.
All we can do in terms of how long any of our fish mught live is to make the effort to give them good parameters, a good diet and to keep the tank in good running condition that they will live longer than if we do not do these things. Our fish only have three real motivations- to stay alive, to find food and to reproduce. And I am not usre if they fail at the last one how much thatmatters to them. After all some fishw ill eat their own eggs or young.
