Sublethal Effects of Hypoxia on Atlantic croaker (Micropogonias undulatus) in the Chesapeake Bay

 Low dissolved oxygen (DO) in water column  Both natural and anthropogenic causes  Increasing global problem

Excess nutrients Large blooms of phytoplankton Excessive bacterial decomposition Warm water temperature Stratification

 Largest US estuary  Long history of hypoxia  Large human impact  Croaker commercially important  Found in hypoxic areas Kemp et al Wicks et al. 2007

 Chesapeake used for industrial, commercial, and recreational purposes  Hypoxia can negatively affect water quality and aquatic organisms (ex. croaker) Croaker !

 Acoustic Telemetry Study: Summer 2011  Lab Hypoxia Study: Summer 2011 & 2012  Field Hypoxia Study: Summer

 Telemetry: Determine behavioral responses between normoxic and hypoxic sites  Lab/Field: Determine physiological effects under hypoxia  Quantify immune, general health, and reproductive effects

 Spring and Summer 2011  Stratified and reference sites  56 fish total  Day and day/night sessions  Vemco VR-100 Receiver  Directional & 360º hydrophones

 V91P-L transmitter (depth sensor)  Benzocaine anesthetic  Surgical implantation  External T-bar tag  Recovery  Release

Tangier Sound (Reference) Point No Point (Stratified)

 Croaker utilize deep channels  Some indication of shallow water use in hypoxic site  Prefer benthic structures (holes, oyster sanctuaries, lighthouses)  Less overall movement in later session  Greater mobility at night

STRATIFIED REFERENCE

 Determine physiological effects under hypoxia  Quantify immune, endocrine, and reproductive effects  Phagocytosis – immune function response  Organosomatic Indices –overall health, immune & reproductive response  Hematology – general health; stress; homeostatic & osmotic balance  Lab trials will determine indicators for use in field study

 24, 48, and 72h trials  1.5 mg/L DO  Hematology  Plasma chemistry  Electrolytes  Complete Blood Count  Differential leukocyte count  Organosomatic Indices  Hepatosomatic (HSI)  Splenosomatic (SSI)  Gonadosomatic (GSI)

 Decreased HSI & SSI in hypoxic fish (48 & 72h)  Indication of stress  Recruitment of blood into circulation  Neutrophilia and lymphocytopenia in 24h hypoxic fish  Innate immune response  Increased glucose *

FIELD SAMPLING LAB TRIALS

Anesthetized fish are bled Blood DrawnBlood put in centrifuge Blood smears Extract plasma Hematocrit WORKSHOP: HEMATOLOGY Plasma chemistry Electrolytes Plasma protein

EYE GILLS PECTORAL FIN PELVIC FIN ANAL FIN CAUDAL FIN FIRST DORSAL SECOND DORSAL LATERAL LINE

LiverGonads Kidney Spleen Swim Bladder Brain & Otoliths Hepatosomatic (HSI) Environmental stress Nutritional status Splenosomatic (SSI) Immune response Blood capacity and transfer Gonadalsomatic (GSI) Gonadal growth Reproductive response

 Studies of Chesapeake Bay and At. Croaker important to understanding human impact on environment  Hypoxia is a growing problem that causes serious behavioral and physiological effects  If we don’t understand more about hypoxia and its effects, this is the result: FISH KILL

Capt. Daniels & El Diablo Luis López-Cruz Eshaddai Ephrem SEEL Ria Mandan Nivette Perez- Perez