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ABSTRACT. Short-term (48 h) exposure of healthy Atlantic salmon Salmo salar L. smolts to infectious salmon anemia (1SA)-inoculated cohort smolts showed that the disease was transmitted with near 100% mortality from Day 7 post-inoculation and onwards. This is more than a week before the inoculated fish show any clinical signs and long before the typical petechial bleedings occur. A bloodborne transmission of the disease is therefore unlikely. Skin mucus, faeces, urine and blood, isolated from ISA-inoculated smolt, transmitted the disease to healthy cohort smolt with variable efficiency depending on how the inoculum was administered. All the sources were infectious and transmitted the disease with high efficiency when injected intraperitoneally (I p.) Into cohort smolt. After i.p. injection, skin mucus had somewhat lower infectivity than blood homogenates. Furthermore, in some experiments application of skin mucus to the gills was as efficient as i.p. inlection for transmission of the &sease When introduced into the stomach none of the inocula caused ISA. Coprophagy thus seems to be ineffective in the transrn~ssion of ISA under laboratory c o n d~t~o n s .Skin mucus from non-inoculated cohabitants exposed to ISA-inoculated smolts for 2 d transmitted the disease with close to 100% efficiency to healthy cohort smolts when injected i.p. This indicates that the infectious agent is waterborne and absorbed by the skin mucus rather than being secreted with the skin mucus. Since healthy smolts have an intact skin barrier, proximity to inoculation directly to the vascular bed seems unlikely. An ultrastructural study of 10 different organs, all in close proximity to the secretions/excretions, revealed that at early stages of the disease, the virus was exclusively found in the pillar cells and endocardial cells. This indicates that the g~lls are the most likely port of entry of the virus. It also supports a causal relation between the observed v~r u s and the disease.

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In the future, if marine science is to achieve any progress in addressing biological diversity of ocean plankton, then it needs to sponsor development of new technology. One requirement is the development of high-resolution sensors for imaging field-collected and in situ specimens in a non-invasive manner. The rapid automatic categorisation of species must be accompanied by the creation of very large distributed databases in the form of high-resolution 3D rotatable images of species, which could become the standard reference source for automatic identification. These 3D images will serve as classification standards for field applications, and (in adjusted optical quality) as training templates for image analysis systems based on statistical and other pattern-matching processes. This paper sets out the basic argument for such developments and proposes a long-term solution to achieve these aims.

Abstract. The gelatinous house of Oikopleura labradoriensis (Tunicata, Appendicularia), collected from the docks of Friday Harbor Laboratories, University of Washington, USA, in 1984USA, in , 1986USA, in and 1990, was examined in vivo by stereomicroscopy and strobe-light macrophotography, and after fixation and processing for light and electron microscopy. In addition to confirming previous knowledge and adding new information on structural organization of the oikopleurid house, this study presents quantitative data on important aspects of its function. Particles small enough to pass through the inlet filters (pore width ~ 13 gin) were concentrated between differently constructed upper and lower food-concentrating filters (pore widths 0.18 and 0.24 gm, respectively). These filtes were held together by an intermediary screen of widely separated ribbon-like filaments. Water sieved through the filters left the house through a pressure-regulated exit valve. However, the intermittent activity of the tail pump and the elasticity of the house caused frequent refluxes of water that cleared both inlet filters and foodconcentrating filter screens of adhering particles. During these refluxes the food-concentrating filters usually collapsed and compacted the trapped particles into coarser aggregates. With each pumping cycle the particles and aggregates were brought closer to the midline. From here they were periodically drained into the mouth of the organism through a medial food-collecting tube, to be recaptured in a pharyngeal feeding filter secreted by the organism's endostyle. Based on the size and movements of the tail within the close-fitting tail chamber, a water flow rate of ~ 0.84 ml min-1 was calculated for medium-sized houses (belonging to individuals with trunk length of ca.