Fish Health in Free Ranging and Captive Environments Parasites, and Pathogens Fish Health in Natural Systems is Relatively New Pursuit Fish biologists have focused on single species Aquatic systems are difficult to study and are often not closed systems Predisposed bias that disease are not important The New Reality Anthropogenic influences Deliberate Introductions Legal Illegal Introductions Inadvertent Introductions Global Climate Changes Habitat Alterations
Paucity and Limitations of Information Studies of fish health of natural populations are rare and generally are begun after a problem. Limited baseline information Problems with sampling techniques and analysis Bias of Pristine Systems Paradigm of natural systems as pure Focus on cultured fish as the bad guy Definitions Epidemiology Epi = upon; demon = people Still used for non human studies Study of how and why diseases and other conditions are distributed within the population
Retrospective study Method of gathering data in which their past histories are examined. Can not find absolute risk, but can determine associations. Prospective Study Gathering data in which one looks for associations. Population is classified and every member is accounted for in the trial. Often called a case control study Prevalence Measurement of all cases of disease at a given time. It includes all new cases and old cases that are still around. Incidence Measurement of only the new cases of a disease or event occurring during a given period. Incidence rates have new cases as numerator and population at risk as denominator. Risk Factor Some factor that increases the risk of disease. Attributable Risk That difference that is attributed to presence of factor.
Vector Anything that actively carries an infective agent Birds, invertebrates, people Vehicle Something that passively carries the agent such as food, contaminated equipment, ships Immune Members of population that have specific or non specific antibodies against the agent. Susceptible Portion of population that can be affected, without immunity and vulnerable to infection. Population Models Host Pathogen Models Susceptible, Infected, Removed HOST DISEASE PATHOGEN PATHOGEN
Susceptible Infected - Removed S-I-R Model Anderson and May 1978 & 1979, and May and Anderson 1978 & 1979 reproduction Susceptible (Uninfected) S (t) transmission Infected I (t) recovery Immune R (t) Mortality R (t) natural mortality Mortality R (t) natural + infected mortality loss of immunity Mortality R (t) natural mortality Threshold Density # Infected # Susceptible Aquatic Disease Models Impact of Ichthyophonus hoferi induced mortality in exploited Clupea harengus 1996) (Patterson Population dynamics of Perkinsus marinus within the Crassostrea virginica host 2000) (Ragone et al. Lepeophtheirus salmonis production in Norway (Heuch and Mo 2001) White spot syndrome virus epidemics in Litopenaeus vannamei (Lotz and Soto 2002)
Disease Modeling Sneizko 1978 HOST ENVIRONMENT ENVIRONMENT ENVIRONMENT DISEASE PATHOGEN PATHOGEN Environmental and other Factors Seasonal variation and temperature effects Discrete vs Continuous time Multiple host Strains/species Carriers Recovery rates, and reinfection Immigration/emigration Predation/competition Fishing mortality Stocking effects Micro and macro habitat Identify the Population or Study Area Define the area of interest? Identify things that are known. Design monitoring and sampling program. Influence of time, seasons, geospatial elements. Identify corridors or exchange areas. What are the trophic exchanges?
Example ECOLOGY OF WHIRLING DISEASE AND MODELING OF RISK Myxobolus cerebralis Life Cycle Build a predictive model of M. cerebralis using GIS based observations and variables and salmonid abundance that includes factors that affect disease severity T. Tubifex HOST ENVIRONMENT ENVIRONMENT ENVIRONMENT Fish Host M. M. cerebralis cerebralis
Study Areas Lemhi River Drainage Pahsimeroi River Drainage Limitations to Fish Distributions Fragmented and Discontinuous Habitat Irrigation Withdrawal Surficial Geology Introduced Salmonid Fish Species Restoration Efforts Pahsimeroi and Lemhi Rivers 2 if 3 chosen Model Watersheds Prioritized for restoration of aquatic habitat for anadromous salmonid utilization Restoration efforts focus on mainstem and tributary reconnection
Tributary Status Lawson C. Trail C. Sulphur C. Morgan C. Grouse C. Meadow C. Morse C. Falls C. Patterson C. Goldburg C. Big C. Discontinuous aquatic habitat Discontinuities and Diversions Discharge (Ft 3 /Sec) at Ellis 350 No Withdrawal October till April 300 Ft 3 /Second 250 200 150 100 50 Irrigation Season April till October 0 2001 2002 2003 Year
Irrigation Canal Networks Stream Irrigation Public Private Used to irrigate 200 km 2 of private agriculture land Used to enhance stream flow in Pahsimeroi River Supply Irrigation Systems Flood irrigation Distribution of Fish Infection Groups of rainbow trout fry exposed in stream for 10 d, removed and reared at Eagle State Fish Hatchery for ~90 days Distribution in Pahsimeroi M. cerebralis detected on the Mainstem Pahsimeroi River and Spring Tributaries Not detected on disconnected Tributaries
Catchment Delineated for each exposure site Surrogate for amount of upstream aquatic habitat Areas of Dewatering Barriers caused by irrigation PBSC-1 Ellis Diversion P-9 P-12 PBSC-1 P9 Ellis Diversion P12 Dewatered Whirling Disease Severity and Catchment Size Average Disease Severity 6 5 4 3 2 1 y = 0.6118Ln(x) - 0.6195 0 1 10 100 1000 Catchment (km 2 ) Log Scale
What Might happen if Tributary Reconnection occurs? Increases in usable aquatic habit for anadromous and resident salmonids Increased instream flows as a result of irrigation consolidation Introduction of M. cerebralis to unaffected areas Lemhi River Another of the 3 Model Watersheds Similar to the Pahsimeroi in many respects Irrigation withdrawals Large alluvial deposits Discontinuities in aquatic habitat Different from the Pahsimeroi Year round flow Seasonal Discontinuous flows in Tributaries 1400 Lemhi Discharge near Mouth 1200 Ft 3 /Second 1000 800 600 Irrigation Season 400 No Withdrawal 200 0 2001 2002 2003 Year
Hydrographs Lemhi and Pahsimeroi 350 1400 Ft 3 /Second 300 250 200 150 1200 1000 800 600 Ft 3 /Second 100 50 0 2001 2002 2003 Year 400 200 00 Surficial Lithography Extrusive Deposition M. cerebralis in the Lemhi Exposures conducted in 2003 Positive Negative
Mean Spore Count (x1000) 350 300 250 200 150 100 50 M. cerebralis intensity in the Lemhi 0 Catchment (km 2 ) Log Scale y = 45.901Ln(x) - 105.48 1 10 100 1000 10000 Summary Positive relationship between catchment size and intensity of M. cerebralis Limitations: Relationships observed were in systems altered by irrigation with inverted hydrographs Habitat restoration efforts must consider risks of increasing M. cerebralis infection intensity if reconnecting reaches
Recently Emerging Diseases Viral haemorrhagic septicemia virus (VHSV) 4 types Single, unique sub-strain occurring in the Great Lakes. Known in Europe, Japan, and the coasts of the U.S. for many years; how it came to occur in the Great Lakes is not known. May have originated in ballast water from ocean-going ships sailing into the Great Lakes, or that it may have hitchhiked in shipments of hatchery-raised fish. Great Lakes In 2005, mortalities appeared in the Bay of Quinte, Lake Ontario and Lake St. Clair. In 2006, VHS has been detected in an increasing number of freshwater fish in Lake Erie, in both Canadian and American waters. Michigan DNR Jan 07 Recent analyses of fish sampled from northern Lake Huron have confirmed the existence of viral hemorrhagic septicemia (VHS) in lake whitefish, walleyes and Chinook salmon, Department of Natural Resources fisheries officials announced today. VHS is a virus that causes disease in fish but does not pose any threat to public health.
Sources There are several known strains of VHS that effect freshwater and marine fish around the world. In North America, VHS strains are found in the marine and estuarine waters of the Pacific and Atlantic. Fisheries and Oceans Canada (DFO) has determined that the VHS virus detected in the Great Lakes is a North American strain, and most closely related to the strain found on the east coast. Control of Spread Anglers and boaters should not move fish, clean boats, trailers, nets, and other equipment when traveling between different lakes and streams. The use of a light disinfectant such as a solution of one part chlorine bleach to 10 parts water. Soaking exposed items such as live wells, nets, anchors, and bait buckets in a light disinfectant for 30 minutes is also an effective method to prevent the spread of a wide range of aquatic nuisance species.