I was watching sea birds eating fishes and wondered if fishes actually died from old age, or if they are all eaten before this can happen?
I reckon some big predator fishes must be able to live long enough to die from their age, but fishes who are lower in the food chain, do any of them actually reach an age old enough to die peacefully or are they all somewhat doomed to feed a bird or another fish?
Answer
Yes, at least some fishes have intrinsic lifespans and deaths that are related to their own life-history and not to external forces such as predation or disease.
Fishes show three types of senescence. Lampreys, eels and pacific salmon exhibit rapid senescence and sudden death at first spawning. The guppy, red panchax, medaka, platyfish, Indian murrel and many other teleosts undergo gradual senescence, as observed in most of the vertebrates. A number of fishes (e.g. sturgeons, paddlefish, female plaice, flatfish, rockfish) show indeterminate growth, the occurrence of senescence in them is supposed to be very slow or negligible.
Patnaik BK, N Mahapatro, and BS Jena. 1994. 'Ageing in fishes' Gerontology 40:113-32
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