Article

Persistence of infection by metacercariae of Apophallus sp., Neascus sp., and Nanophyetus salmincola plus two myxozoans (Myxobolus insidiosus and Myxobolus fryeri) in coho salmon Oncorhynchus kisutch.

Department of Microbiology, Oregon State University, Corvallis, Oregon 97331, USA.
Journal of Parasitology (Impact Factor: 1.26). 12/2009; 96(2):340-7. DOI: 10.1645/GE-2289.1
Source: PubMed

ABSTRACT We evaluated the ability of 5 muscle- or skin-dwelling parasites to persist in naturally infected coho salmon, Oncorhynchus kisutch, from the West Fork Smith River, Oregon, by holding them in captivity from late summer to early spring (parr stage to the typical time of smoltification). These parasites included metacercariae of 3 digeneans, Nanophyetus salmincola, Apophallus sp., and neascus sp., and 2 myxozoans, Myxobolus insidiosus and Myxobolus fryeri. Two groups of wild-caught fish were evaluated in the laboratory, i.e., heavily infected fish from the lower main stem and less severely infected fish collected from tributaries of this river. All parasites survived in these fish for the 7-month experiment. Only 2 parasites had a statistically significant lower median abundance between host life stages. The mean abundance of N. salmincola declined 45% in the tributary fish and Apophallus sp. declined 43% in the lower main stem fish. However, more than 50% of each species persisted until the end of the study, with smolts still harboring relatively high infections.

0 Followers
 · 
77 Views
  • Source
    • "Muscle and kidney samples were thawed and the entire amount of tissue weighed. We placed a subsample of muscle tissue (4.5–6.3 g) or the entire posterior kidney (0.02–0.24 g) between two pieces of Plexiglas with a small amount of water, and applied pressure to create a wet mount (Ferguson et al. 2010). We then examined the slide under a compound microscope to identify and enumerate parasites. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Anadromous salmonids are viewed as a prized commodity and cultural symbol throughout the Pacific coast of North America. Unfortunately, several native salmonid populations are threatened or at risk of extinction. Despite this, little is known about the behavior and survival of these fish as the juveniles transition from freshwater to the ocean. Our primary objectives were to estimate survival of juvenile steel-head migrating between trapping sites and the ocean and evaluate whether survival in the estuary varies temporally (within a year) or spatially (within and between estuaries) within the same distinct population segment. We also evaluated whether flow or fork length were correlated with survival and collected information on variables that have been demonstrated to affect smolt survival in other studies to lend insight regarding differences in survival estimates between basins. We compared run timing, migration rate, sur-vival, condition factor, age composition and time of residence in the estuary for steelhead outmigrants from each basin and measured parasite loads in outmigrat-ing steelhead to evaluate potential differences in par-asite density and parasite community between basins. In 2009, we implanted acoustic transmitters in 139 wild steelhead smolts in two small rivers on the Ore-gon Coast. In general, only 40–50 % of the wild steelhead smolts tagged at upstream smolt traps were detected entering the ocean. The majority of mortality occurred in the lower estuary near the ocean. Wild steelhead smolts typically spent less than 1 day in Environ Biol Fish
    Environmental Biology of Fishes 05/2013; 96:849-863. DOI:10.1007/s10641-012-0080-8 · 1.36 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Graduation date: 2011 Nearly 3000 juvenile Chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon captured in nearshore waters off the coasts of Washington and Oregon from 1999-2004 were tested for infection by Renibacterium salmoninarum, Nanophyetus salmincola, and skin metacercariae. First, three quantitative PCR primer/probe sets were compared for detection of R. salmoninarum; amplification of the single copy abc gene was best at detecting medium-high levels of infection and was used in subsequent studies. Parasite infections were detected visually. Infection by N. salmincola was the most common single infection among all juvenile salmon (55.2%), followed by R. salmoninarum (27.5%) and skin metacercariae (16.5%). Infection by R. salmoninarum was highest in 2000, with 54.8% of all juvenile salmon infected, and was much lower in 2004 (<10%). Subyearling (but not yearling) Chinook salmon infected by N. salmincola had significantly reduced growth; skin metacercarial infection was associated with significantly reduced growth only for coho salmon. Infection by R. salmoninarum was associated with significantly reduced growth in yearling Chinook salmon and coho salmon. Multiple infections did not have significantly more severe effects on growth than single infections, although the prevalence of triple infections was very low. The prevalence of R. salmoninarum was significantly and positively correlated with increased survival for both yearling Chinook and coho salmon. To better understand the apparent paradox that higher prevalences correlate with increased survival, we examined the effects of ocean conditions using the summer Pacific Decadal Oscillation (PDO) index as an indicator of good (cold) or bad (warm) ocean condition years. The years 1999-2002 were cold ocean years, and 2003-2004 were warm ocean years. The prevalence of R. salmoninarum was significantly higher in cold years, when ocean conditions were favorable, and more salmon with severe infections were captured; there was no effect of infection on growth. In the summers of warm years, infected yearling Chinook and coho salmon had significantly reduced growth, and the prevalence and severity of R. salmoninarum infections declined. These data indicate that the infection is less detrimental in years with favorable ocean conditions, and suggest that R. salmoninarum infection may be a mechanism linking ocean indices to salmon survival.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Population viability analysis (PVA) can guide conservation management and research by identifying the cheapest and most effective actions required to conserve populations and by prioritising research. The usefulness of a very preliminary PVA model is illustrated here for managing New Zealand mainland colonies of sooty shearwaters Puffinus griseus, a long-lived seabird that is preyed on by small carnivores and harvested by Maori for food. The model suggests that chicks can be safely cropped for transfer to depleted colonies, or for human consumption from the two large Otago colonies with populations exceeding the most conservative MVP of 520 individuals. The model also helps direct managers to where and when predator control will be most efficient. It predicts that predation of adults is more likely to have a greater effect on growth rates and MVPs than chick predation. Therefore, funding should be directed towards predator control at the beginning of the season when adults are most vulnerable. However, the model cannot determine population trends, nor rightly assure conservation managers that predator control is essential or even sufficient to prevent extinction. Preliminary models can assist by formalising how uncertain our current understanding is, but should not be expected to work a miracle of divining certainty from a lack of field information that still may take decades to collect. Less reliance should be placed on the predictions of population trends or extinction probabilities than on the model's guidance to the relative efficacy of different management actions.
    Biological Conservation 01/1995; 73(2-73):107-117. DOI:10.1016/0006-3207(95)90033-0 · 4.04 Impact Factor
Show more