Old fish. What is an old fish? I am not sure but I do know that some fish live a really long time. How long? Real long, like over 20 years. I think most larger fish can live much longer than that but the small fish we normally keep seem to have a much shorter lifespan. From my experience tangs can live well into their twenties but I have never kept one longer than about 14 years. After that they seem to have accidents. Even percula clowns live over 20 years. Some types of fish have very short lifespans like seahorses and pipefish. I can not keep seahorses more then about 3 years. Of course they are probably a couple of years old when I collect them so I am not sure of their lifespan. Pipefish also, just a few years although the bluestripe I have now is about 3 or 4.
Why am I thinking about this?
I think about all sorts of useless things and I just came back from a nice day on the water on my boat and as I was watching the bunker (menhaden) jump all around the boat, the thought hit me. How long do these things live?
As I look at my tank I have a watchman gobi about 5" long. He is about 12 or 13 years old and was part of a breeding pair. I got the pair when they were very young and after countless spawnings the female disappeared. I am assuming old age but fish get heart attacks, strokes, cancer and a bunch of other things. I am going with old age. I have no Idea how long watchman gobies are supposed to live but people are supposed to live to about 78 years or so. We all know that some of us die much younger and so do fish. My remaining watchman gobi is showing his age. He was very active for most of his life, scouring the bottom for food at night and coming to the glass in the daytime at feeding time. Now he kind of lays around waiting for me to squirt some food at him. When he grabs it, it is not with the same vigor that I am accustomed to seeing. He also chews for a long time before he takes another bite. Just like old people. He is clearly old and even has lines on his face. No really. I have noticed this twice before on two different fish. One was a 14 year old percula clown that was one of my first fish in the 70s and one was a 13 year old figure eight puffer that was my very first saltwater fish. He was actually bought in fresh water and then my tank was converted to brackish and then salt.
I once had a brutlyd or cusk eel who lived to 18 before I killed him in an accident. I don't remember if he had any lines but maybe his lifespan was 30 or 40 years, I don't know.
The watchman gobi is still very healthy and his blue spots seem like neon lights. Thats one way to tell a healthy fish, their colors seem irridescent and not dull.
My 17 year old fireclown does not seem to be showing his age as much but I can start to see the slight lines in his face and he is slowing down a bit. I also have a much younger fireclown and you can easily tell from their faces that this one is only half the age of the other one.
Now I know that fish do not age like us and they have much different skin so don't think I rub Oil of Oley on their faces but you cna definately tell an old fish from their face.
OK stop laughing, it's true.

Here they are young


And Old

This is so interesting! A testament to your good care as well. I think fish aren't usually thought of as having long life.. it's a shame when they are treated as being so replaceable. I think of legendary bass & other gamefish known to live 30-40 years or more in lakes in Florida where I grew up.. I think it can be challenging to keep fish in small quarters & have them live a full happy life, so big kudos to ev'one who's successful like this!

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90 gal freshwater- Jurupari & Goby community (the Lizard Lounge)

5 gal freshwater- SS Shiny at Threadie's beach

Lisa it seems that if they live two weeks, they will live forever. Fish usually die right away because of either collection techniques or shipping practices. Some just can't acclimate to captivity, I don't blame them.
I think the biggest problem is that we don't feed fish what they are supposed to eat and many people just feed flakes or pellets. Fish fed on just that will never be healthy and will always be at risk for disease. A healthy fish in breeding condition rarely gets any type of disease including paracites, they settle down and go about their business of eating and looking for a mate, two things that healthy fish do every day. Fish in that condition will live to die of old age.
They will only get in that condition by eating fresh, preferably live sea food. I feed live blackworms every day along with new born live brine shrimp. I suppliment that with fresh clams and mysis. Some of the fish and corals get pellets soaked in fish oil.
It seems to work because I almost never find a dead fish. They all either die from an accident or old age.