摘要:

The chromosomes in the cells of 1–2‐day‐old cod embryos were studied using light microscopic techniques. The observations revealed slightly non‐synchronous cell divisions, with at least three different mitotic phases present in a 1‐day‐old embryo. Surprisingly high percentages of abnormal metaphases and anaphases were found in normal‐looking embryos. In the 2‐day‐old embryos, free‐lying nuclei were observed in the periblast zone. Chromosome studies of these nuclei revealed a cleavage pattern of the chromosomes which differed from that

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05250.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

An additional and hitherto undescribed ipnopid genus and species,Discoverichthys praecoxMerrett and Nielsen, is reported and described, and its relationships with the family and aspects of its biology are discussed.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05251.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The feeding periodicity of juvenile coho salmon,Oncorhynchus kisutch, was examined from stomach collections taken during five sampling periods in coastal waters off Oregon. Significant differences in stomach content weight were found between several consecutive 3‐hour periods, with peak fullness occurring in early morning and around dusk. The rates of gastric evacuation of euphausiid meals were measured in the laboratory at two temperatures. The decline in stomach contents was best described by an exponential model: 90% evacuation of the wet weight contents required an estimated 28.4 and 18.1 h at 11.4 and 13.7° C, respectively. The method of Elliott&Persson was used to estimate a daily ration of 2.4 and 3.7% of the wet body weight at the two temperatur

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05252.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Food intake was measured under conditions of continuous food availability for haddock,Melanogrammus aeglefinus(L.), and dab,Limanda limanda(L.). Haddock consumed approximately 75% of all food during the day, with a peak of feeding at dusk and an inferred peak at dawn; peaks of feeding were associated with larger meals. By contrast, dabs were mainly night‐time feeders with daily consumption rates that were approximately 40% lower than those shown by haddock. Comparison of haddock maximum daily ration with published estimates of consumption in the wild indicate that wild haddock feed at between 15 and 22% of their maximum capacity. Using published data on gastric evacuation, the relationship between meal size and stomach residuum was investigated. There was no detectable relationship between these two variable

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05253.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The feeding of brook and brown trout in a temperate Canadian stream was studied over two winters. Stomach analyses indicate that feeding continues throughout the winter. Both species had similar diets. Despite continuous feeding, condition factors declined significantly in early winter and remained low until the spring, suggesting an early‐winter depletion of lipid reserves. Energy (calorific) intake was similar in winter to that found in late summer or spring and therefore was not the cause of low winter condition. The derived energy from feeding was insufficient to offset the costs of maintenance metabolism in the early winter period, for both immature and recently spawned fish. It is suggested that stream‐dwelling trout suffer a metabolic deficit during acclimation to rapidly declining water temperatures in November/December. Such a phenomenon has important physiological implications for overwinter survi

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05254.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

A trap for catching migrating lampreys in running water is described. It is based on a double‐funnel system and uses standard, readily available, plastic and brass materials. The trap is inexpensive, portable and easy to install and hide, even in shallow, fast‐flowing water. It has been found to be more successful than the other traps with which it was compared in field trials and is highly selective for lampr

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05255.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Methods for the collection, fixation, preservation and examination of the cestodes parasitic in British freshwater fishes are described. An illustrated key to the species is provided, with the exception of the members of the genusProteocephalus, for which the information is tabulated.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05256.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Small groups of juvenile Atlantic cod,Gadus morhuaL., were kept at 14°C in through‐flow tanks and were fed known quantities of a compounded diet of natural food. The cod were fed single and multiple meals with ration size in the range 0.5 to 4.1% of total wet fish body weight. Ammonia production in each feeding experiment was monitored continuously.For single‐meal experiments, significant relationships were derived between ration size and (a) total ammonia excreted, (b) total exogenous ammonia excreted above endogenous excretion levels, (c) duration of the elevated phase of ammonia excretion, (d) maximum rate of ammonia excretion, and (e) time delay after feeding to reach maximum rate of ammonia excretion. Relationships between nitrogen loss as ammonia and nitrogen intake were examined and estimates of endogenous excretion rate and maintenance ration made.Repetitive feeding resulted in cyclical variation in ammonia excretion. At the lowest ration size, ammonia excretion rates had nearly returned to the pre‐feeding level within 24 h. At higher feeding levels, the effect of each successive meal tended to be cumulative, resulting in increasingly higher ammonia excretion rates which only stabilized towards the end of the exper

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05257.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The classic Homer Smith divided box experiment (Smith, 1929) was repeated upon five marine and one freshwater teleost species. Of the nitrogenous output (as ammonia and urea), 50–70% occurred in the head region for marine teleosts, while the freshwater tilapia studied excreted 90% from the head. Together with the data of Smith, these data indicate that nitrogen excretion by the gills is of lesser importance in marine teleosts than in freshwater species.In the dab,Limanda limanda, the head, anus and urinary opening were all in the anterior chamber of the divided box, but 47% of nitrogen excretion still occurred in the posterior chamber, presumably across the skin. In the blenny,Blennius pholis, exposed to air, the head region accounted for 46% of urea elimination, and 26% of ammonia outpu

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05258.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Annual changes in the population size of the metacercariae ofTylodelphys podicipinain the eyes of perch in a small eutrophic lake were studied over ten years by following changes in prevalence, abundance and overdispersion of parasites throughout the life of each year class of fish. The population increased rapidly in the first two years after its introduction to the lake, but for the next six years fluctuated within very narrowly constrained limits before declining as a result of a catastrophic decline in the perch population. No evidence of parasite‐induced host mortality was found: the decline in parasite abundance throughout the life of each year class was due to density‐independent parasite mortality within the fish as a result of natural variation in the life span of the metacercariae. Levels of infection in the first year of a year class were determined principally by transmission processes, as transmission could only occur over a very brief period when release of cercariae from parent generation snails coincided with the presence of perch fry. Transmission appeared to be density‐independent, and infection levels in perch to be determined by the dimensions of the transmission’ window’ and subsequently modified by parasite mortality. No evidence of host responses or any other regulatory factor of fish origin was found, and the infrapopulations in perch appear to be non‐equilibrial and unstable. Although the possibility of regulatory processes acting on infrapopulations of the parasite in other hosts remains, the importance of transmission windows in determining infrapopulation levels in fish is

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05259.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY