Ultrastructural aspects of infestation by Ichthyobodo necator (Henneguy, 1883) on the skin and gills of the salmonids Salmo salar L. and Salmo gairdneri Richardson

Abstract. Ultrastructural changes in the skin and gill epithelia of Salmo salar L. and Salmo gairdneri Richardson caused by Ichthyobodo necator are described. Sloughing of Malphigian cells and epidermal spongiosis result in the characteristic clinical signs of costiasis. Destruction of subsurface cells may facilitate rapid development of spongiosis. Infested surface cells show dramatic degeneration of the cytoplasm but the nucleus usually remains intact. It is concluded that I. necator does not feed specifically on the nucleus.     

Serum and red cell folate and serum vitamin B12 levels in horses

SUMMARY Vitamin B12 and folate concentrations were determined by radioimmunoassay in groups of horses in Queensland. Highest serum vitamin B¹² levels were found in supplemented performance horses. These, together with pastured horses that included pregnant and lactating mares, had significantly greater serum folate activity than permanently stabled animals. The range of red cell folate concentrations was much narrower in horses in training than from any other group. Red cell folate may be a better indicator of a horse's folate status than the serum folate value. Vitamin B¹² and folate concentrations were highest in spring and summer. Small intestinal dysfunction in 2 horses was not associated with vitamin B¹² or folate malabsorption. Serum folate levels returned to normal 24 h after intramuscular injections of 75 to 150 mg folic acid, whereas serum vitamin B¹² values remained elevated for at least one week following injections of 8 to 10 mg to non-supplemented horses.     

Sward maintenance of Lolium multiflorum by slurry seeding

A field investigation into the effect of slurry seeding on the dry-matter yield and persistence of an Italian ryegrass sward was assessed over a 3-year period (1984–86) under a regime of three cuts per season combined with sheep grazing in early spring and late autumn. Results showed that slurry plus seed treatments produced up to 30% more herbage dry matter and a significantly higher tiller density than where no slurry or seed were used. Slurry application with and without seed also reduced the proportion of weed grasses ( mainly Poa spp.) in the sward. It is concluded that slurry seeding is a useful technique for extending the productive life of an Italian ryegrass sward.     

Pathogenesis and autoradiographic studies of the epidermis of salmonids infested with Ichtyobodo necator (Henneguy, 1883)

Abstract. The sequential pathology of Ichtyobodo necator infestations of the skin of 0+ and 1+ salmon and rainbow trout was studied. Areas of greatest shelter from water currents were found to be most commonly infested and no parasites were found attached to the epidermis on the head of the fish. The parasite caused hyperplasia of the malphigian cells and exhaustion of the goblet cells below infestations, followed by spongiosis of the underlying epidermis. The epidermal plaque then sloughed off leaving a single layer of cells attached to the basement membrane. Cell kinetic studies showed that I. necator caused the cells immediately below infestations to divide, a markedly different pattern from that of normal teleost epidermal cell proliferation. The possibility that the parasite secretes some form of digestive enzyme is postulated. In areas where sloughing had occurred, the remaining malphigian cells were seen to be in the process of division.     

Seed survival and periodicity of seedling emergence in four weedy species of Papaver

Seeds of Papaver argernone, P. dubium, P. lecoqii and P. rhoeas were collected in each of three or four years and mixed with the top 7·5 cm of sterilized soil confined in cylinders sunk in the ground outdoors and cultivated three times yearly. Except for P. argemone, no more than 6% of seeds produced seedlings in the autumn of sowing; seedling numbers were usually greatest in the following year and then decreased exponentially from year to year. Mean survival of viable seeds after 5 years ranged from 7·4% for P. lecoqii to 2·0% for P. argemone. Most seedlings of all four species emerged in early spring and early autumn; emergence of P. rhoeas was greater in spring than in autumn, but the reverse was true for the other three species.