ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00661.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Improved production of 1+Atlantic salmon,Salmo salarL., smolts can be achieved by taking advantage of the species’ plasticity in response to environmental variables and the timing of physiological events leading to smolting. Smolting commences during the season of declining photoperiod, dependent on reaching a threshold size, after which underyearling populations develop bimodality in length frequency distribution, the upper and lower modal groups (UM, LM) completing smolting at ages 1+and 2+, respectively. We discuss the application of photoperiod and thermal manipulation in relation to the environmental and biological requirements for effective smolting. Such manipulation may be used to promote growth, increasing the incidence of fish attaining threshold smolt size and development of bimodality, followed by completion of smolting the following spring. Growth dynamics and the ‘decision’ to commence smolting are discussed in relation to size thresholds leading to a brief growth surge resulting in UM status. An enzymatic bioassay is described for studying growth during thse short periods of rapid growth associated with the commencement of smolting. Sexual maturation in male parr is discussed in relation to smolting; evidence is presented that parr which become sexually mature during autumn are capable of completing smolting the following spring, together with previously immature fish, provided they reach certain size thresholds near the time of mat

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00662.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Trials were run to determine the immunomodulatory effect of dietary vitamin C in rainbow trout.Oncorhynchus mykiss(Walbaum), and Atlanticsalmon,Salmo SalarL. We first investigated whether depletion of ascorbic acid (AA) could depress the immune system. Subsequently, we focused our studies on the stimulatory effect of a high dietary dose of stable vitamin C derivatives (1000mg AA‐equivalent per kg of feed) in order to determine their prophylactic role.Three trials were run with rainbow trout fed, for periods of time varying from 2 to 6 months, a high dietary dose of ascorbate‐2‐polyphosphate (AAPP) or L‐ascorbate‐2‐monophosphate calcium salt (AAMP) equivalent to 1000mg AA per kg of feed. The high dietary level of vitamin C was compared to 60mg AA‐equivalent per kg of feed. Another experiment was conducted with Atlantic salmon pre‐fed AAPP at 60mg/kg for 6 months followed by AAPP at 1000mg/kg for 2 months. Various immune parameters were tested such as mitogen‐induced proliferation, serum complement level, phagocytosis and natural cytotoxicity. Leucocyte and plasma AA contents were also determined.The immune response in vitamin‐C deficient trout was not strongly different from that in trout fed the minimal growth requirement level. Serum complement level was not affected by vitamin C. A high dietary dose of vitamin C was found to increase trout and salmon leucocyte AA content, mitogen‐induced proliferation of lymphocytes, and chemiluminescence response of leucocytes with a higher constancy, when the cells were stimulated with opsonized zymosan and with luminol as a substrate. Natural cytotoxicity was enhanced in trout fed a high dietary dose of vitamin C. The results of these immunity studies support supplementation levels of vitamin C which are much higher than the minimal requirement known to prevent deficiency symptoms and promote normal growth. Further investigations on the time‐dose response are needed to define quantitatively the high di

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00663.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Supplementary enzymes were added to a diet in order to increase its digestibility and improve the growth achieved by seawater Atlantic salmon,Salmo salarL. The supplementary enzymes were selected to hydrolyse proteins and carbohydrates. Three diets, with fishmeal as the only source of protein (C1), with fishmeal and soybean meal (C2) and diet C2 with supplementary enzymes (C3) were fed to seawater salmon (100g) for 12 weeks at nominal tank rations equivalent to 2·5% body weight per day. Consumption rates of individual fish were measured by radiography. The salmon fed C3 had higher rates of food consumption, significantly higher final weights and rates of growth and lower food conversion efficiencies and maintenance ration than those fed C2. Salmon fed C1 had similar food conversion efficiencies to the C3 fed fish. These results indicate that the addition of supplementary enzymes to diets containing soybean meal improves the growth and food conversion efficiency of salmon

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00664.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Molecular cloning methods and strategies which have been employed to reveal the exact nature of antibodies (immunoglobulins) and major histocompatibility complex (MHC) antigens from Atlantic salmon,Salmo salarL., have been discussed briefly. As in other fish species, the immunoglobulin heavy chain (IgH) of the Atlantic salmon has the typical characteristics of the IgM heavy chain from higher vertebrates. The membrane form of IgH is somewhat special, as the mRNA splicing pattern excludes the fourth constant exon, generating a membrane‐anchored IgM one domain shorter than the mammalian counterparts. This splicing pattern has also been reported from cod and catfish, and seems to be general for teleosts. Notably, Atlantic salmon possess two isotypic IgM heavy chain constant region genes. The presence of two closely related IgH genes is in accordance with the quasi‐tetraploid state of the Atlantic salmon genome, which means that the entire gene complex is probably duplicated. As deduced from phylogenetically conserved amino acid residues and the pattern of polymorphic residues, MHC antigens from Atlantic salmon seem to parallel those from higher vertebrates. Improvement of disease resistance in aquaculture stocks is discussed in relation to MHC polymorph

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00665.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.We have investigated the effect of a salmon farm on the local benthos and the benthic environment. The bottom fauna was examined before establishment in March 1988, during operation in September 1989 and April 1990, and after closure in March‐April 1991. During this time 2417 tonnes of salmon were produced. The samples were collected from two stations within 250m of the farm site. The sediment contained mainly clay and silt, the organic content varied from 9·1 to 17·3% and there was no increase in the organic content during the sampling period.The bottom fauna in 1988 was rich and relatively similar at both stations. The species number close to the farm declined from 65 in 1988 to only 11 in 1989. A year after the fish farm was moved, the number of species had risen to 29.The fish farm clearly influenced the bottom fauna in the immediate vicinity of the site but no effect was found at 250 m distance. The environmental conditions had improved in 1991 after abandonment of the site, but the fauna had not returned to the status measured before operations began in 1

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00666.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.It is becoming increasingly clear that cultivated salmon will not perform the way we want them to unless we have a thorough understanding of how the rearing environment will affect their behaviour. This paper illustrates some of the behavioural patterns that can influence feeding and growth rates, and how these may differ between individual fish. A salmon's appetite is not simply a function of temperature: there are complex daily, seasonal and developmental appetite rhythms, which result in some fish becoming anorexic while others continue to feed. The developmental switches which trigger some fish to become anorexic (and so delaying smolting) appear to be irreversible, but individual differences in behaviour in the period leading up to the switch point influence whether fish smolt early or late. Thus more competitive and dominant fish are more likely to become S1 smolts, and these differences in dominance status become established within the first few weeks of feeding. They appear to have a physiological basis: fish with higher metabolic rates (irrespective of initial size) tend to be dominant, and so subsequently grow faster. However, the extent of these behavioural effects will depend on the rearing environment. The challenge is therefore to allow all fish to feed without intimidation, and to devise feeding schedules which take account of complex appetite rhythms — only then will we be working with the fish, rather than against the

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00667.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Life‐history strategies are means by which animals solve the problems of successful reproduction in varying environments. Their development patterns are consequences of responses to the opportunities the environment offers them. Understanding them requires an understanding of the way they evolved, their ontogenetic development, their physiological control, and their adaptive value. The present paper views the salmonids as marine fishes, which have radiated into fresh water through using river beds as protected spawning grounds. It also takes the view that the maturation process has priority over somatic growth in fish, and that it has already been initiated by the time of first feeding. Its completion is environmentally dependent, and can be arrested annually. Whether or not it will be arrested depends on the status of the energy stores of the individual at particular critical times of year. This mechanism has adaptive value both for immediate reproductive success — adequate energy to provision the next generation — and for later overwinter survival, ensuring that if energy stores are inadequate for reproduction they are spared. Atlantic salmon show variation in their reproductive patterns, and examples are given from laboratory and aquaculture experiments to demonstrate some environmental controls which result in these variations. A hypothetical model is presented to account for the operation of these con

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00668.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Recent attempts to apply selective breeding strategies in fish populations have focused on the genetic effects of selection. The basic mechanisms of long‐term response to selection are discussed with reference to experience from laboratory and farm animal populations. A simplified polygenic model is presented, and it is shown that considerable response may be obtained for polygenic traits without essential changes in allele frequencies and genetic variability, and that the probability of fixation of alleles or genotypes because of selection will be low when the trait is affected by a larger number of loci. The span between the extreme fixed genotypes for such traits may easily become wider than that which may be realized under normal biological conditions. This is illustrated with some examples from Atlantic salmon.Salmo salarL. The effects of divergent fitness selection of populations on genetic differentiation and allele frequencies are also considered, and some examples from experiments with Norwegian river strains of Atlantic salmon are discussed. It is shown that the river strains are not expected to differ much in frequencies of fitness alleles if the number of loci affecting the fitness trait is large, and that considerable overlapping of genetic values for fitness between strains may be expecte

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00669.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.An increase in mortalities, due to the failure of some smolts to feed after transfer to sea cages, has been observed in many fish farms during the last 2 years. In the present study mortalities were as high as 9–5% and the majority of these appeared 7–9 weeks post‐transfer. Comparisons of length‐weight relationships between the initial group of smolts released in the cage and at 3‐, 6‐ and 8‐wcek intervals after transfer showed that a proportion of the fish had lost weight. The condition factor of individually measured fish also confirmed that with increasing time after transfer some fish were in a much poorer condition.The feeding of smolts after transfer was not related to their size. The fork length distribution of feeding and non‐feeding fish showed that feeding fish were recruited from all size classes of the initial population.The lack of appetite in smolts after transfer was demonstrated by the reduced number of fish feeding and by the amount of food consumed. In the first week after transfer only 10% of the fish were feeding in the sea cage, increasing to 65% after 5 weeks. In the tanks (where there were no failed smolts) 95% of the smolts were feeding within 5 weeks after transfer, whereas in the sea cage it took 8 weeks before this fig

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00670.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY