Do they grow 1 kg per year, and does that mean a 150kg fishy is 150 years old - a claim I have seen ?
I don’t think weight correlates linearly with age. According to this… “Halibut live a long time. Females grow faster and live longer than males. The oldest recorded female was 42 years old and the oldest male was 27 years old.”
Keep in mind this is a single source.
This one was 495 lb, and there are rumours of up to 700 lb: if you are adopting one as a pet, it would be safer in a small lake than an aquarium in your bedroom: however you will find it both loyal and loving, and always ready for a watery romp on a dark moonlit night.
I don’t know about a Halibut in particular, but many fish live very long like that. I assume the 1 kilogram per year is just an average, probably growing more rapidly when young and then growth rate slows for the rest of it’s life.
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Not the all-time record, but my dad held the record for largest fish caught with rod-and-reel in Alaska for one particular year, with a halibut he caught while stationed at Kodiak. IIRC, it was over 300 pounds. I’m sure the newspaper article is lying around here somewhere.
Why determine the age of a fish?
Just for the halibut.
Up to the point before “golden brown and delicious”.
Yep, the white sturgeon is noted for living to (at least) 100+ years old, and can easily be many hundreds of pounds at just 6-8’ long, IME. I used to do LOTS of multi-day sturg fishing camp-outs on Snake River just below Hagerman, Idaho and my buddies and I would semi-routinely catch 8-10+ foot+ ‘monsters’ in certain holes below big rapids we knew about. This was in mid-late ‘90’s. fwiw. At times, it could take most a of a day/night just to get them monsters to the shore without them stripping the reel’s line almost clean off again. And yes, I do have pics, but not scanned, fwiw.
The bigest we ever caught was over 11’ feet easily as measured by the rod(s) we used but shook free from our hook/grasp just as the pole was laid alongside it for a pic (dammit!), so we had no verifiable evidence other than around 8 people seeing it in person. There was easily a foot or two more (decades of growth overall, in my understanding), at least, of tail length left at end of rod as fish shook free from four people trying to hold it reasonably still against rocky shore. My wife would no longer go swimming/rafting with us after seeing first-hand what what lurked below, LOL.
Fish and Game (who knew and treated us well) often stopped by in their jet boats to see what size we were catching due to their periodic hatchery releases and to see if the sturg were breeding in wild - anything less than 18" (IIRC) was born wild, and we got some of those occasionally, which is great. Always catch/release, of course, with big ol’ hook’s barb bent fully to shaft before baiting, etc.
And another piece of ‘trivia’ is that Fish and Game (who allowed us to take dead fish from hatcheries near Thousand Springs unannounced as sturg bait anytime we wanted) told us that a hatchery-raised rainbow trout gains about 80% in weight of the weight of food they eat (efficiency of intake-v-growth) while in early to middle life, then weight-gain tapers off slowly as trout ages. I forget what rate the sturg has but it was MUCH lower, significantly lower, IIRC. Fish and Game guys also told us that the biggest of the sturg we were catching were at least 100+ years old based on their previous studying of their aging and that the hugest/oldest of them (lots longer than 12-13’ feet) were taken long before catch and release/management went into effect, unfortunately.
Sorry to get off the halibut topic, but yes, some fish in fresh water get HUGE.
Here is another that claims a 55 year old - as estimated by counting otolith growth rings.