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The pathogenicity of Vibrio mimicus for two commercially cultured species of Australian freshwater crayfish, the yabbie Cherax albidus and the red claw Cherax quadricarinatus was investigated . Total aerobic mesophilic bacterial counts were obtained from hemolymph extracted from live crayfish . Bacteria were found in the hemolymph of 100% of C. albidus and 98% of C. quadricarinatus sampled; 45% and 54% of each species, respectively, had concentrations of more than 100 colony-forming units/mL . Aeromonas, Acinetobacter, Vibrio, Micrococcus, and Staphylococcus were the predominant bacterial genera isolated from both species of crayfish . Vibrio mimicus was isolated from 14% of the C. albidus sampled over 3 months . Three of seven V. mimicus isolates were virulent and produced rapid mortalities when 10 5 viable cells were inoculated into crayfish by intramuscular injection. Inoculation with lysed cells and filtered culture supernatants produced no mortalities. Ribotyping was used to study relationships among the V. mimicus isolates . Eleven ribotypes were observed among 18 isolates with different pathogenicity for crayfish. We confirmed that strains of V. mimicus present in the aquaculture environment can produce systemic disease in two commercially cultured species of crayfish .

SAUNDERS, R. M. K. & FOWLER, K., 1992. A morphological taxonomic revision of Azolla Lam. section Rhizosperma (Mey.) Mett. (Azollaceae). Recent research on the agronomically important aquatic fern Azolla has been hampered by the lack of a sound taxonomic framework. The classification of section Rhizosperma is revised using multivariate statistical analyses of ultrastructural, gross morphological and anatomical characters. The disparate morphologies and current delimitations of A. pinnata and A. nilotica are corroborated. Three distinct geographically related subspecies of A. pinnata are identified and formally named and described as: 1. subsp. pinnata, occurring in northern and eastern Australia and New Caledonia; 2. subsp. asiatica subsp. nov., occurring in India, southern China, south‐east Asia and southern Japan; and 3. subsp. africana stat. et comb, nov., occurring in tropical Africa and Madagascar. A sequential dichotomous key is provided for the identification of taxa, with new taxonomic descriptions.

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Megaspore germination and embryo development in Azolla filiculoides was examined using SEM and thin–sectioning. Within the released megaspore apparatus, resting cells of the endosymbiont Anabaena azollae Stras. arc located distally to the outside of the mcgasporangial wall and adhering to the inside of the megasporocarp wall. Growth of the female gametophyte displaces the floats pushing this part of the wall (the indusial cap) upwards, so providing access to the archegonia for the multifiagellalc spermalozoids. Embryo development and its inoculation with Anabaena involves a subtly–timed sequence of events resulting in the perpetuation of the symbiosis. Growth of the lunnel–shaped cotyledon leaf ruptures the mcgasporangial wall to provide access and a channelled route between the Anabaena and embryo shoot apex; subsequent leaf development severely restricts such access. During this process, the Anabaena is dislodged by the cotyledon leaf and growth of the first leaf traps the now actively–dividing Anabaena colonv; this becomes established around subapical trichomes from where filaments become incorporated into the cavities of developing leaves. The voung sporophyte rises vertically to the water surface as a result of gas accumulation in intercellular spaces; at no stage do floats endow buoyancy.