Geology topics
Publications and source records attributed to S. F. Snieszko.
Review of: Taschenbuch der Fischkrankheiten, fu?r Fischereibiologen, Tiera?rzte, Fischzu?chter und Aquarianer. Erwin Amlacher. Jena, Fischer, 1961. xi, 286 p. illus.
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Commercial and laboratory‐prepared capillary tubes for hematocrit were tested. A 10 percent solution of heparin was found to be best for the preparation of treated capillary tubes. For examination of trout blood laboratory‐prepared capillary tubes were found to be superior to commercial tubes which are designed for human blood. Sharp, pointed heparinized capillary tubes were used with good results for collecting blood from the heart without killing the examined fish. Hematocrits determined directly in such tubes were found to have the same value as those prepared in other ways.
Use of radioisotopes has increased rapidly in hydrobiology and fish culture. Their use, especially P 32 , to study circulation of nutrients has been demonstrated and offers opportunities in problems of lake metabolism. The most extensive use of isotopes has been to determine photosynthetic activity in plankton through C 14 uptake. Applications and limitations are discussed. Isotopes have been successfully used in food studies of fish to determine food selection, metabolism, and storage. Water movements in fresh and salt water and in sewage problems have been successfully followed by use of various isotopes. Marking of aquatic animals with radioisotopes has many possible applications, but has been little used because of some inherent problems related to danger to organisms and in field use. Extent of future use of isotopes in hydrobiology will be determined by further study of hazards and public acceptance of field studies.
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To determine if pancreatic necrosis is a communicable disease of trout, lots of eyed brook trout eggs were obtained from four hatcheries. Pancreatic necrosis appeared spontaneously in trout from one of these hatcheries and the other strains were exposed to infection by suspension prepared from diseased fish. In all cases, typical pancreatic necrosis appeared in fish exposed to infection and the control fish remained healthy. Disease was more acute in fry fed brine shrimp nauplii than in those fed beef liver. Mortality data suggest that susceptibility to pancreatic necrosis decreases with the increased age of trout. No treatment for the disease is known, but sanitary measures were effective in preventing its spread.
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Illness, in fish as well as in other animals, when caused by an infectious disease, is often not the result of infection with pathogens alone. In many cases the pathogens and hosts can exist side by side without development of disease symptoms. Such symptoms, with resulting illness or death, appear only when the balance of mutual tolerance between the host and the pathogen is shifted in favor of the pathogen. Factors of several different kinds may render a host susceptible to disease; such things as poor nutrition, unfavorable physical conditions in the environment and the hereditary make‐up of the fish itself. Drugs may allow temporary control of infectious diseases but for the long‐range control it is better to increase the resistance of the host. Some suggestions are given, based largely on experience with disease control in hatcheries and fish farms, for minimizing natural mortality of fish from infectious diseases.
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