Development, growth, and survival data derived from laboratory experiments are provided for Lepeophtheirus salmonis, a common ectoparasite of wild and sea-farmed salmonids. The mean development time of eggs was 419-1 hours (17-5 days) at 5°C, 207-1 hours (8-6 days) at 10°C, and 130-8 hours (5-5 days) at 15°C. Development from the first nauplius to the infectious copepodid stage took 222-3 hours (9-3 days) at 5°C, 87-4 hours (3-6 days) at 10°C, and 44-8 (1-9 days) hours at 15°C. Development from the egg to the adult male took 40 days, and from the egg to the adult female 52 days at 10°C. No egg development occurred at 10%o salinity. At 15%o eggs developed but failed to produce active nauplii. At higher salinities (20-30%o) active nauplii were produced, but copepodids were only obtained at 30%o. Copepodids survived for less than 1 day in waters with a salinity of 10%o or less. At higher salinities (15-30%o) and temperatures of 5,10, and 15°C average survival times ranged between 2 and 8 days.

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Lepeophtheirus salmonis (Copepoda: Caligoida) is an economically important marine ectoparasite of wild and pen-reared salmonids. The morphology of its developmental stages is described and compared with that of other species of Lepeophtheirus and Caligus. The development of L. salmonis is very similar to that reported for other Lepeophtheirus species. The appendages generally attain the adult condition and the sexes become distinguishable later in development than in Caligus species. At all developmental stages except the nauplius, L. salmonis can be distinguished from the co-occurring Caligus clemensi.

Seawater, marine surface sediment, fecal material of the sea cucumber Parastichopus californicus, and kelp blades of Macrocystis integrifolia were treated with formaldehyde to strengthen the bacterial cells, followed by tetrasodium pyrophosphate addition and sonication to disperse these same cells. These cells were then stained with 4′,6-diamidino-2-phenylindole and counted by epifluorescent microscopy. The technique of strengthening the cells with an aldehyde and then dispersing them in a suspending medium using a deflocculent (pyrophosphate) and ultrasound caused the bacteria to be randomly distributed when filtered onto Nuclepore membranes with a lower variance within and similar variance between subsamples as compared with untreated samples. In most cases the coefficient of variation stabilized after the bacterial cells in 10 randomly chosen microscopic fields had been counted. Sediment bacterial numbers (±SE) determined by the standard technique were 5.20 (±0.36) × 1010 per gram wet weight; by this dispersion technique they were 11.30 (±0.24) × 1011 per gram, a greater than twofold increase. On young and intermediate aged kelp blades, the increased counts which resulted from this dispersion technique ranged from two- to five-fold. Bacterial cells which were epiphytic on a senescent blade and could not be counted at all by the standard technique were determined to be 3.77 (±0.14) × 106 cm−2 using this dispersion method.

Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease (BKD), can be transmitted vertically (i.e. from parent to progeny) and horizontally (i.e. from fish to fish). The purpose of this study was to investigate the role of the fecal-oral route of horizontal transmission among farmed salmon held in seawater. Horizontal transmission probably explained the significant increase in prevalence of Rs observed within a regularly sampled population of chinook salmon Oncorhynchus tshawytscha held in a seawater netpen. Viable Rs was detected In the seawater sampled from within a netpen of BKD-affected chinook, and once shed into seawater survives long enough to be ingested by neighbouring fish. The feces from these fish appeared to be the source of Rs in the seawater. Survival experiments revealed that Rs remained viable in seawater for up to 1 wk. A fecal-oral route of horizontal transmission was demonstrated by orally intubating Rs-laden feces into young coho salmon 0. kisutch. The Rs-intubated group experienced significantly higher BKD-related mortality than the control group: 98 and 7 0 % , respectively. This study indicates that the fecal-oral route of horizontal transmission may contribute significantly to the increasing prevalence of BKD in farmed salmon.

ABSTRACT-The yolk material of coho salmon Oncorhynchus lusutch eggs contains at least 1 naturally occurring antibactenal factor -lysozyme. The antibacterial properties of this lysozyme were studied with selected bacterial flsh pathogens. It was found to be rapidly bactericidal to Aeromonas hydrophila, Aeromonas salmonic~da, and Carnobacterium piscicola at a concentration of 700 pg ml-l, a concentration approximately one-third of that found in the yolk of most salmonid eggs. However, the lysis that ~t caused with the test bacterium Micrococcus lysodeikticus did not occur with the foregoing fish pathogens. The kidney disease bacterium Renibacterium salmoninarum was not killed when incubated with as much as 1900 pg ml-' of the enzyme for 90 min. The data presented indicate that the antibacterial role of lysozyme should not be equated merely with its ability to lyse microorganisms, and that lysozyme has a role in preventing the mother to progeny (vertical) transmission of some bacterial fish pathogens. Its failure to kill R. salmoninarum helps to explain why this organism is readily vertically transmitted.

ABSTRACT. The effects of hydrocortisol implants on the susceptibility of naive coho salmon Oncorhynchus kisutch to infection with the economically important marine ectoparasitlc copepod Lepeophtheirus salmonis was investigated under laboratory conditions. Cortisol-implanted coho salmon were more susceptible to infection than the control coho salmon. Copepods were lost from the gills of the control coho salmon by 10 d post-infection, and only a few remained on the body and fins at 20 d post-infection. Copepods were retained on the gills, fins and body of the cortisol-implanted coho salmon over the 20 d studied. Histological sections of control coho gills and fins revealed well developed epithelial hyperplasias and inflammatory responses to the presence of L. salmonis. The magnitude of the inflammatory response and the development of epithelial hyperplasia was suppressed in the cortisol-implanted coho. These data support the hypothesis that non-specific host defence mechanisms are important in resistance of coho salmon to infection with L, salmonis.

The occurrence of lysozyme in the eggs of coho salmon Oncorhynchus kisutch is reported for the first time. The eggs were shown to contain high levels of the enzyme, the concentration In the yolk being 1900 pg ml-l. Purification of the enzyme was achieved using chitin-coated cellulose and gel filtration. Only one active molecule was isolated and it was shown by SDS-PAGE to have a molecular weight of 14.5 kD. Similar levels of lysozyme were found in the eggs of 2 other species of salmonids also tested. The significance of the egg yolk lysozyme is dscussed with respect to its role as a natural defence factor against microorganisms, particularly bacteria.