AGING IN FISHES

Fishes show three types of senescence. Lampreys, eels and pacific salm on exhibit rapid senescence and sudden death at first spawning. The gu ppy, red panchax, medaka, platyfish, Indian murrel and many other tele osts undergo gradual senescence, as observed in most of the vertebrate s. A number of fishes (e.g. sturgeons, paddlefish, female plaice, flat fish, rockfish) show indeterminate growth, the occurrence of senescenc e in them is supposed to be very slow or negligible. Neuroendocrine me chanisms are involved in rapid senescence. Most of the evidences in fa vour of the occurrence of senescence in fishes have been derived from studies in species showing gradual senescence. Age-related increases i n mortality rate, accumulation of lipofuscin, lipid peroxidation, coll agen cross-linking and decreases in growth rate, reproductive capacity and protein utilisation are clearly marked in such species. Anatomica l changes in various organs during ageing also confirm increases in de generative changes and pathological symptoms. Dietary restriction and lower environmental temperature retard the ageing processes in a few s pecies showing gradual senescence. These results tentatively support t he contention of commonality in mechanism of ageing processes in verte brates. At present, anatomical, cellular, biochemical and genetic evid ences in support or against the occurrence of slow senescence or negli gible senescence in long-lived fish species are almost nonexistent. Ex tensive studies on ageing in fishes are needed to explain the multiple mechanisms which are not unexpected considering the number and variet y of the existing species.