This study assessed the suitability and cost e⁄cacy of an equal blend of canola oil (CO) and poultry fat (PF) as a supplemental dietary lipid source for juvenile Atlantic salmon. Quadruplicate groups of Atlantic salmon ( $ 400 g) held in 4000 L outdoor ¢breglass tanks supplied with running (35^40 L min À1 ), aerated (dissolved oxygen, 7.88^10.4 mg L À 1 ), ambient temperature (8.6^10.9 1C) sea water (salinity, 263 5 g L À1 ) were fed twice daily to satiation one of three extruded dry pelleted diets of equivalent protein (488^493 g kg À1 dry matter) and lipid (2672 74 g kg À1 dry matter) content for 84 days. The diets were identical in composition except for the supplemental lipid (234.7 g kg À1 ) source viz., 100% anchovy oil (AO; diet COPF-0),70.2% AO and 29.8% CO and PF (diet COPF-30), and 40.3% AO and 59.7% CO and PF (diet COPF-60). Atlantic salmon growth rate, feed intake, feed e⁄ciency, protein and gross energy utilization, percent survival and whole body and ¢llet proximate compositions were not a¡ected by diet treatment. Cost per kilogram weight gain was about 10% less for ¢sh fed diet COPF-60 than for diet COPF-0. Percentages of saturated fatty acids in dietary and ¢llet lipids varied narrowly. Moreover, percentages of 18:1n-9, monounsaturated fatty acids, 18:2n-6, n-6 fatty acids,18:3n-3, and ratios of n-6 to n-3 fatty acids in the £esh lipids were directly related to the dietary level of CO and PF whereas 22:6n-3, the total of 20:5n-3 (eicosapentaenoic acid; EPA) and 22:6n-3 (docosahexaenoic acid; DHA), and n-3 fatty acids revealed the opposite trend. Percentages of 22:6n-3, EPA and DHA, and n-3 fatty acids were signi¢cantly depressed in ¢sh fed diet COPF-60 versus diet COPF-0.We conclude that a 1:1 blend of CO and PF is an excellent cost-e¡ective dietary source of supplemental lipid for Atlantic salmon in sea water.

Eighty coho salmon Oncorhynchus kisutch smolts (40 wild and 40 hatchery-reared) were surgically implanted with acoustic transmitters and released into the Quinsam River over 2 days. Differences in physiology, travel time and migratory behaviour were examined between wild and hatchery-reared fish. In addition, tagged and control fish of both wild and hatcheryreared stock were raised for 3 months following surgery to compare survival and tag retention. Detection ranges of the acoustic receivers were tested in the river, estuary and ocean in a variety of flow conditions and tide levels. Receivers were placed in the river, estuary and up to 50 km north and south from the river mouth in the marine environment. Wild smolts were significantly smaller by mass, fork length and condition factor than hatcheryreared smolts and exhibited significantly higher levels of sodium, potassium and chloride in their blood plasma than hatchery-reared smolts. The gill Na þ K þ -ATPase activity was also significantly higher in the wild coho smolts at the time of release. Ninety-eight per cent of wild and 80% of hatchery-reared fish survived to the estuary, 8 km downstream of the release site. No difference was found in migration speed, timing or survival between smolts released during daylight and those released after dark. Wild smolts, however, spent less time in the river and estuary, and as a result entered the ocean earlier than hatchery-reared smolts. Average marine swimming speeds for wild smolts were double those of their hatchery-reared counterparts. While hatchery smolts dispersed in both a northward and southward direction upon entering the marine environment, the majority of wild smolts travelled north from the Campbell River estuary. The wild coho salmon smolts were more physiologically fit and ready to enter sea water than the hatchery-reared smolts, and as a result had higher early survival rates and swimming speeds.

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.

No abstract

As the timing of spring productivity blooms in near-shore areas advances due to warming trends in global climate, the selection pressures on out-migrating salmon smolts are shifting. Species and stocks that leave natal streams earlier may be favoured over later-migrating fish. The low post-release survival of hatchery fish during recent years may be in part due to static release times that do not take the timing of plankton blooms into account. This study examined the effects of release time on the migratory behaviour and survival of wild and hatchery-reared coho salmon (Oncorhynchus kisutch) using acoustic and coded-wire telemetry. Plankton monitoring and near-shore seining were also conducted to determine which habitat and food sources were favoured. Acoustic tags (n = 140) and coded-wire tags (n = 266,692) were implanted into coho salmon smolts at the Seymour and Quinsam Rivers, in British Columbia, Canada. Differences between wild and hatchery fish, and early and late releases were examined during the entire lifecycle. Physiological sampling was also carried out on 30 fish from each release group. The smolt-to-adult survival of coho salmon released during periods of high marine productivity was 1.5- to 3-fold greater than those released both before and after, and the fish's degree of smoltification affected their downstream migration time and duration of stay in the estuary. Therefore, hatchery managers should consider having smolts fully developed and ready for release during the peak of the near-shore plankton blooms. Monitoring chlorophyll a levels and water temperature early in the spring could provide a forecast of the timing of these blooms, giving hatcheries time to adjust their release schedule.