Studies of the host-parasite interaction between carp and saprolegnia
The thesis compares the effects of temperature and substrate on
the growth of fish pathogen Saprolegnia diclina and the saprophyte
Saprolegnia ferax. Studies revealed optimal growth of both species
occurs at 20-25'C depending upon the substrates used. Growth is
restricted at higher and lower temperatures. For both species
optimum growth was recorded on medium containing 1% casein and 1%
glucose, but high levels of lipid and glucose inhibited growth.
exhibits a higher growth rate than S. ferax at
high lipid concentrations.
S. diclina produces more proteolytic activity per unit weight at
100C than S. ferax, regardless of substrate. S. diclina also
demonstrated greatest lipase activity at 10°C, particularly in the
presence of casein or lipid. These factors may facilitate
colonisation of fish tissues by S. diclina at low temperatures.
Carp maintained at 10° C showed greater infection by S. diclina,
than carp kept at 20°C. Evidence is presented for a lack of
antibody production in infected carp maintained at 10°C. Fish kept
at 20°C only produced antibody to Saprolegnia antigens when they
were coupled to erythrocyte carriers. During infection phagocytic,
macrophages and neutrophils increased; there was a decrease in the
numbers of mucous secreting goblet cells in the skin, and lymphoid
organs showed increased pigment deposition.
Infected fish showed evidence of physiological stress including
decreased levels of erythrocytes, haemoglobin, liver glycogen and
protein, and an increase in liver lipid. Ascorbic acid levels
decreased in interrenal tissue.
Histological and scanning E. M. studies of skin lesions provide
new information about changes in the surface during UDN disease.
Key words: Saprolggnia infection and UDN