ISSN:0304-324X    

DOI:10.1159/000213578

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Homeotherms exhibit programmed ageing correlated with their determinate mode of growth and the natural attrition of irreplaceable functional units in vitally essential organs. Poikilotherms are potentially capable of indefinite growth, can supplement their populations of functional units, and may therefore not be subject to the inherent depreciations of ageing. Comparative studies may enable us to determine which group is the exception to nature’s rul

ISSN:0304-324X    

DOI:10.1159/000213579

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

It is possible to determine the age of fishes with reasonable accuracy by reading the ‘growth rings’ (annuli) in hard parts (scale, otolith, opercular bone, vertebra and cross-section of dorsal or pectoral spine and fin rays). Primary growth increments in ‘otoliths’ can also be used as an alternative method of age determination. The traditional methods could be supplemented with more reliable fmorochrome and microradio-graphic techniques. The suitability of the use of hard parts and the techniques may vary among the species. It is essential that the ‘true rings’ be distinguished from other types of rings, such as false rings, larval rings and spawning rings through repeated examination of samples to avoid confusion and inaccuracy in age determination. The causes and the periodicity of ring formation may vary from species to species. The growth history of fishes could be traced by back calculation of length attained at different ages. Among the different types of growth equations, the Von Bertalanffy’s model appears to be the most suitable for fishes of both temperate and tropical regions. With slight modification, the same model may also serve to estimate the maximum theoretical calculated age (longevity) of fishes. The longevity of fishes show wide variations. The life-span may be short, intermediate and long. Whereas the lowest range of life-span (1-2 years) is exhibited by some species of lampreys and teleosts, there are species of dogfishes, sturgeons, paddlefishes, rockfishes and eels which have the life-span (70-152 years) in the highest range. A number of factors (size, sex, temperature, diet, reproduction, age at maturity and genetic composition) are believed to influence the longev

ISSN:0304-324X    

DOI:10.1159/000213580

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Fishes exhibit a ‘determinate’ type of growth in short-lived species of warmer regions and an ‘indeterminate’ type in long-lived species of colder regions. Growth is measured in units of length and weight and is best represented as the specific growth rate. The relationship between weight and length provides an index of the state of well-being of a fish (condition factor ‘K’). Growth could also be measured by using certain other criteria such as glycine uptake by scales, hepatosomatic index, RNA:DNA ratio and protein retention in the tissues. Nutrition, including the quality and quantity of food, plays a significant role in growth regulation. A number of environmental factors, such as temperature, oxygen concentration, salinity and photoperiod, influence the rate of growth. Recent data suggest that genotypes, hormones and physiological conditions of the individual are also equally important endogenous regulator

ISSN:0304-324X    

DOI:10.1159/000213581

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

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, rock-fish) show indeterminate growth, the occurrence of senescence in them is supposed to be very slow or negligible. Neuroendo-crine 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.

ISSN:0304-324X    

DOI:10.1159/000213582

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Methods of age determination of amphibians by counting annual layers in the bone tissue and data on longevity of amphibians (both anurans and urodeles) in nature are presented. Age compositions of amphibian populations are discussed and their variations analysed.

ISSN:0304-324X    

DOI:10.1159/000213583

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The complex life history of many amphibians has been designed to take advantage of the resources of two completely different habitats. The aquatic free-living amphibian larva is different from the terrestrial adult regarding morphology, physiology and behavioural patterns. Therefore, in the lifetime of an individual amphibian, two discontinuous growth stanzas are exhibited. The sigmoid growth model fits well with both stanzas. The rapid growth of the larval amphibian can be described by the double exponential Gompertz equation, whereas the slow growth process of the transformed amphibian can be described by the von Bertalanffy growth model. The bulk of amphibian growth occurs in the terrestrial phase and is not independent of size, age, sex and environmental conditions. The endocrine regulation of growth in amphibians is unique in the sense that the mechanism of pituitary action is different in aquatic and terrestrial phases.

ISSN:0304-324X    

DOI:10.1159/000213584

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Limited research findings up-to-date with a few amphibian models do not permit a generalisation of ageing phenomena in the class Amphibia. Short-lived species of amphibians show gradual senescence comparable to the pattern seen in laboratory mammals. Long-lived species (mostly urodeles) continue to grow throughout life and are believed to exhibit very slow or negligible senescence which is unobtrusive. In a few species with gradual senescence, there is some evidence of an increase in mortality rate and a decrease in growth rate with advancing age. Increase in cross-linking of collagen, accumulation of age pigments (lipofuscin and melanin), decrease in metabolism and loss of immunocompetence are ageing phenomena common to both amphibians and mammals. On the other hand, persistence of neurogenesis and myogenesis, continuance of oogenesis beyond adult life and polyphyodonty are some of the features peculiar to ageing in amphibians. More authenticated reports are needed to fill up the gaps in our knowledge on amphibian senescence.

ISSN:0304-324X    

DOI:10.1159/000213585

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

After a brief recall of the classical meaning of the concept of longevity, the first part of this chapter describes and summarises the main current technique for the estimation of age in reptiles. Among them, sclerochronology is primarily taken into account. The cautious analysis of seasonal growth cycles recorded in hard tissues, although not as rigorous as the mark-release-recapture method of animals in their natural conditions, now appears as a rapid and reliable chronological tool already successfully used in individuals of many reptile species. Sclerochronology is especially efficient for the comparison of several populations, and it is the only method for fossils. The second part presents a synthetic review of known longevities and records in the different groups of reptiles. A short discussion about the significance of longevity shows that for reptiles, because of their thermic metabolism (ectothermy), the physiological longevity must be strongly distinguished from the chronological longevity, especially for a comparison with that known for birds and most mammals.

ISSN:0304-324X    

DOI:10.1159/000213586

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

This paper reviews the literature on growth in reptiles. The current consensus is that growth data for small and medium-sized reptiles are best fitted by logistic-by-mass equations, data for larger reptiles by the von Bertalanffy equation. Experiments on the relationships between behavioural thermoregulation, food consumption and growth in both the laboratory and field are described, and an account is given of some recent work on individual differences in growth rates and their adaptive significance. In general, it may be said that in almost all areas of biology relating to growth, less is known about reptiles than about equivalent phenomena in fishes.

ISSN:0304-324X    

DOI:10.1159/000213587

出版商:S. Karger AG    

年代:1994

数据来源: Karger