Ageing in fishes.

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. Neuroendocrine mechanisms are involved in rapid senescence. Most of the evidences in favour of the occurrence of senescence in fishes have been derived from studies in species showing gradual senescence. Age-related increases in mortality rate, accumulation of lipofuscin, lipid peroxidation, collagen cross-linking and decreases in growth rate, reproductive capacity and protein utilisation are clearly marked in such species. Anatomical changes in various organs during ageing also confirm increases in degenerative changes and pathological symptoms. Dietary restriction and lower environmental temperature retard the ageing processes in a few species showing gradual senescence. These results tentatively support the contention of commonality in mechanism of ageing processes in vertebrates. At present, anatomical, cellular, biochemical and genetic evidences in support or against the occurrence of slow senescence or negligible senescence in long-lived fish species are almost nonexistent. Extensive studies on ageing in fishes are needed to explain the multiple mechanisms which are not unexpected considering the number and variety of the existing species.

Age-dependent changes in some aspects of glutamate metabolism in the brain of the teleost, Channa punctatus. I. Ammonia and glutamine contents and glutamate dehydrogenase activity.

Age related changes in some aspects of glutamate metabolism were followed in the brain of a short lived species of tropical murrel, Channa punctatus. Both ammonia and glutamine contents of brain increased with advancing age of the murrel. The glutamate dehydrogenase activity of brain increased during maturation phase (year classes 0(+)-3+) followed by a decline in senescence phase (year classes 3(+)-6+). The pattern of age changes in glutamate metabolism in this species of fish shows similarity with the observations made in a majority of mammalian species, thereby suggesting a commonality in a basic metabolic mechanism during aging process in the central nervous system of vertebrates.