Shannon K. Balfry

Recent Salmon Declines: A Result of Lost Feeding Opportunities Due to Bad Timing?

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 fishs 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.

Immunotoxicological effects of a sub-chronic exposure to selected current-use pesticides in rainbow trout (Oncorhynchus mykiss)

Many current-use pesticides (CUPs) are found at increasing concentrations in aquatic environments, yet relatively little is known about their effects on the immune system of fish. We examined the in vivo effects of three pesticides (chlorothalonil, cypermethrin and pentachlorophenol) on the immune system of juvenile rainbow trout (Oncorhynchus mykiss) by assessing a suite of innate immune function tests, as well as a host resistance test using Listonella anguillarum. Increased activity of phagocytic leukocytes, as evidenced using flow cytometry, was observed following 28-day exposures to pentachlorophenol (1 microg/L and 2 microg/L), but not for cypermethrin or chlorothalonil, although a trend of increasing activity was noted for chlorothalonil. No recovery was observed during a 14-day post-exposure chlorothalonil experiment, as evidenced by continued elevation of respiratory burst and percent phagocytic cells at the lowest exposure concentrations (100 ng/L and 200 ng/L), suggesting a prolonged CUP-induced impact on the immune system. No effects of any pesticide on body weights, direct lethality, serum lysozyme or relative leukocyte differential were observed, suggesting that modulation of the cellular responses of the innate immune system represents a sensitive sub-lethal endpoint for these three pesticides. However, a lack of detectable effects of these CUPs on host resistance to L. anguillarum in our study may reflect a dose-response range that did not elicit an effect on those immune responses responsible for control and clearance of this particular pathogen. Additional research may provide more insight into the immunomodulatory effects of these and other CUPs, and the implications for host resistance against a variety of bacterial, viral and macroparasitic pathogens.

Use it or lose it? Sablefish, Anoplopoma fimbria, a species representing a fifth teleostean group where the βNHE associated with the red blood cell adrenergic stress response has been secondarily lost

SUMMARY Like most teleosts, sablefish (Anoplopoma fimbria Pallas 1814) blood exhibits a moderate Root effect (~35% maximal desaturation), where a reduction in blood pH dramatically reduces O2 carrying capacity, a mechanism important for oxygenating the eye and filling the swim bladder (SB) in teleosts. Although sablefish lack a SB, we observed a well-defined choroid rete at the eye. The adrenergically mediated cell swelling typically associated with a functional red blood cell (RBC) β-adrenergic Na+/H+ exchanger (βNHE), which would normally protect RBC pH, and thus O2 transport, during a generalized acidosis, was not observed in sablefish blood. Neither isoproterenol (a β-agonist) nor 8-bromo cAMP could elicit this response. Furthermore, RBC osmotic shrinkage, known to stimulate NHEs in general and βNHE in other teleosts such as trout and flounder, resulted in no significant regulatory volume increase (RVI), further supporting the absence of a functional RBC βNHE. The onset of the Root effect occurs at a much lower RBC pH (6.83–6.92) than in other teleosts, and thus RBC βNHE may not be required to protect O2 transport during a generalized acidosis in vivo. Phylogenetically, sablefish may represent a fifth group of teleosts exhibiting a secondary reduction or loss of βNHE activity. However, sablefish have not lost the choroid rete at the eye (unlike in the other four groups), which may still function with the Root effect to oxygenate the retina, but the low pH onset of the Root effect may ensure haemoglobin (Hb)-O2 binding is not compromised at the respiratory surface during a general acidosis in the absence of RBC βNHE. The sablefish may represent an anomaly within the framework of Root effect evolution, in that they possess a moderate Root effect and a choroid rete at the eye, but lack the RBC βNHE and the SB system.

The association between metabolic rate, immune parameters, and growth performance of rainbow trout, Oncorhynchus mykiss (Walbaum), following the injection of a DNA vaccine alone and concurrently with a polyvalent, oil-adjuvanted vaccine

This research demonstrates a significant increase in routine metabolic rate (RMR) following injection of a DNA vaccine concurrently with a polyvalent, oil-adjuvanted vaccine. The increase in RMR was transient and associated with increased activity of both the non-specific and specific immune responses. Rainbow trout (Oncorhynchus mykiss) were injected with a DNA vaccine (DV), a commercially available polyvalent, oil-adjuvanted vaccine (AV), or the two vaccines in combination and sampled at 203, 305, and 406 days (dd) post-vaccine injection (pvi) for RMR and key immune parameters (serum lysozyme activity, serum neutralization antibody titres). The RMR of fish that received both the DV and the AV was significantly higher at 203 dd pvi, compared to fish from all other treatment groups which included the control, the AV, and the DV groups. The increased RMR corresponded to elevated levels of serum lysozyme activity and an earlier seroconversion of virus-specific neutralizing antibodies. To determine if growth performance was affected by the transient increase in RMR, specific growth rate (SGR), percent daily weight gain (WG), and feed conversion ratio (FCR) were determined at 798, 1204, and 1610 dd pvi. Although fish in all three vaccine groups showed significant increases in SGR and WG at 798 and 1610 dd pvi compared to the control group, the overall weight of the fish was not different at the end of the experiment. In summary, this study shows that concurrent injection of a DV and an AV transiently increases the RMR of rainbow trout and changes the manner in which the immune response occurs, but does not affect the overall growth performance of the fish.

Disease resistance and health parameters of growth-hormone transgenic and wild-type coho salmon, Oncorhynchus kisutch

To extend previous findings regarding fish health and disease susceptibility of growth-enhanced fish, hematological and immunological parameters have been compared between growth hormone (GH) transgenic and wild-type non-transgenic coho salmon (Oncorhynchus kisutch). Compared to non-transgenic coho salmon, transgenic fish had significantly higher hematocrit (Hct), hemoglobin (Hb), mean cellular hemoglobin (MCH), mean cellular volume (MCV), and erythrocyte numbers, and lower white cell numbers. In addition, resistance to the bacterial pathogen Aeromonas salmonicida (causal agent of furunculosis) has been assessed between the strains. Higher susceptibility of transgenic fish to this disease challenge was observed in two separate year classes of fish. The present findings provide fundamental knowledge of the disease resistance on GH enhanced transgenic coho salmon, which is of importance for assessing the fitness of transgenic strains for environmental risk assessments, and for improving our understanding effects of growth modification on basic immune functions.

The Effect of Hatchery Release Strategy on Marine Migratory Behaviour and Apparent Survival of Seymour River Steelhead Smolts (Oncorhynchus mykiss)

Early marine migratory behaviour and apparent survival of hatchery-reared Seymour River steelhead (Oncorhynchus mykiss) smolts was examined over a four year period (2006–2009) to assess the impact of various management strategies on improving early marine survival. Acoustically tagged smolts were released to measure their survival using estuary and coastal marine receivers forming components of the Pacific Ocean Shelf Tracking (POST) array. Early marine survival was statistically indistinguishable between releases of summer run and winter run steelhead races, night and day releases, and groups released 10 days apart. In 2009, the survival of summer run steelhead released into the river was again trialed against groups released directly into the ocean at a distance from the river mouth. Apparent survival was improved significantly for the ocean released groups. The health and physiological status of the various release groups were monitored in years 2007–2009, and results indicate that the fish were in good health, with no clinical signs of disease at the time of release. The possibility of a disease event contributing to early marine mortality was further examined in 2009 by vaccinating half of the released fish against common fish diseases (vibriosis, furunculosis). The results suggest that marine survival may be enhanced using this approach, although not to the extent observed when the smolts were transported away from the river mouth before release. In summary, direct experimental testing of different release strategies using the POST array to measure ocean survival accelerated the scientific process by allowing rapid collection of data which enabled the rejection of several existing theories and allowed tentative identification of several new alternative approaches that might improve early marine survival of Seymour River steelhead.

Growth and performance of Atlantic salmon, Salmo salar L., following administration of a rhabdovirus DNA vaccine alone or concurrently with an oil-adjuvanted, polyvalent vaccine

This research demonstrates for the first time an absence of growth-related side effects in Atlantic salmon, Salmo salar L., following the injection of a DNA vaccine alone or concurrently with a commercially available, polyvalent, oil-adjuvanted vaccine. Using weight and specific growth rate measurements, individually tagged Atlantic salmon were monitored for 2028 degree days (dd) post-vaccination. During this time, DNA-vaccinated fish did not differ in weight, length, condition factor or specific growth rate compared to unvaccinated control fish. While differences in weight were observed between unvaccinated control and concurrently vaccinated fish, there were no significant differences in weight, length, condition factor or specific growth rate between concurrently vaccinated fish and adjuvant-vaccinated fish, suggesting that only adjuvant vaccination affected growth. To further determine if concurrent injection of a DNA vaccine and a polyvalent, oil-adjuvanted vaccine had a physiological impact on the Atlantic salmon, swimming performance tests were performed at 106 dd post-vaccination with U(crit,1), U(crit,2), the U(crit) recovery ratio (RR) and the normalized RR being similar to values obtained from unvaccinated control fish. In summary, this study shows that concurrent injection of a DNA vaccine and a polyvalent, oil-adjuvanted vaccine does not negatively influence the growth or swimming performance of Atlantic salmon compared to adjuvant vaccination alone.

Concurrent injection of a rhabdovirus-specific DNA vaccine with a polyvalent, oil-adjuvanted vaccine delays the specific anti-viral immune response in Atlantic salmon, Salmo salar L.

Vaccines are commonly used in salmonid aquaculture as a method of disease prevention. Although there is a substantial amount of published research regarding the immunological and physiological effects following the injection of different polyvalent vaccines and DNA vaccines, there are no published reports examining the physiological and immunological effects of concurrent vaccine injection, which is the situation encountered in aquaculture. Using key immunological parameters such as lysozyme activity and specific antibody titres we examined the short-term activation of the immune response of cultured Atlantic salmon (Salmo salar L.) following concurrent injection with a traditional, polyvalent, oil-adjuvanted vaccine (AV) and an IHNV-specific DNA vaccine (DV). Our results indicate that different aspects of the innate and adaptive immune responses are influenced in either a positive or negative manner. While concurrent vaccine injection elicited an increase in lysozyme activity, changes in antibody titre (Ab) were antigen specific. The production of anti-Aeromonas salmonicida Abs was significantly greater in the combined vaccine group at 296 degree days post-vaccine injection (dd pvi), while the production of anti-Listonella anguillarum Abs was significantly greater at 106 dd pvi in the combined vaccine group. Of even greater interest was the apparent delay in production of IHNV-specific neutralizing antibodies (NAb) when the DV was injected concurrently with the polyvalent AV. The results indicated that concurrent injection of a polyvalent oil-AV and a DV can be beneficial to the production of antibodies; however, the specific anti-viral response may be delayed.

Effects of dietary lipid substitution on swimming performance during the early developmental stages of Chinook salmon (Oncorhynchus tshawytscha)

The marine fish oils present in farm feed not only comprise a substantial proportion of the cost of aquacultural salmon production, they are also responsible for the accumulation of anthropogenic contaminants in the fish, such as PCBs and dioxins. Our study looks to assess the practicality of substituting these marine fish oils with canola oil, a vegetablederivative which has the potential to decrease feed costs in salmon production, as well as reduce levels of harmful contaminants present in the fish. Over seven months, four groups of Chinook salmon (Oncorhynchus tshawytscha) were fed one of four diets differing in their respective canola oil/anchovy oil ratios (0/100, 25/75, 50/50, and 75/25 total lipid content). These ratios, as well as the feeding of the fish earlier in development, was to supplement a previous study investigating the effects of dietary lipids on fish physiology so as to further investigate the effects of canola oil replacement. Swimming performance was measured for the fish of each group through the determination of their critical swimming velocity (Ucrit), and from these values the overall physical condition of the fish could be inferred. Upon fatiguing, other indicators of osmoregulatory stress were measured in the fish, including gill Na+/K+ ATPase activity and morphology, plasma osmolarity, Na+, Cl, and muscle water content. No significant differences between the diets have been found regarding the fishes’ swimming performance or muscle water content, suggesting canola oil as a viable substitute for anchovy oil in Chinook salmon.