CINEMar/Open Ocean Aquaculture Annual Progress Report for the period 1/01/05 through 12/31/05
Principal Investigator: David L. Berlinsky, George Nardi
I. Accomplishments
A. Scheduled Tasks
Our research objectives for this project were to:
1. Develop protocols to measure the stress response in larval and juvenile cod
2. Identify the ontogeny of the stress response in larval cod
3. Describe the time course of the stress response in juvenile cod
4. Determine the effect of salinity depression on the acute stress response in juvenile cod
5. Reduce stress during larval and juvenile culture
6. Monitor health of juvenile cod, with emphasis on nodavirus prevention
B. Progress on Tasks
1. Methods and protocols to measure cortisol, glucose, osmolality and total protein in plasma (large fish) and whole body homogenates (larvae and small juveniles), in response to stress, were successfully developed and validated. These parameters accurately determine the degree of stress a fish experiences following a procedure such as transport or vaccination.
2. Cortisol, the major stress hormone in teleost fish, was measured in cod following a known stressor (30 second netting), during larval and juvenile development. Cortisol was measured in larval fish at hatch, and days 8, 14, 19, and 23 post-hatch. Cortisol was also measured in response to a stressor in small (~5 grams) and larger (~30 grams) juvenile cod.
3. The duration of the stress response was determined by stressing groups of juvenile cod and measuring cortisol at 0.5, 1, 3, 6, and 24 hours following the stressor.
4. As osmoregulation in full strength seawater requires a considerable energy expenditure and may exacerbate a stressor, we tested the effect of pre-acclimating fish to moderately-depressed (20 ppt) saline conditions, in an attempt to reduce stress.
5. Stress has been shown to predispose fish to diseases transmitted by opportunistic pathogens. To determine if stocking density influences stress level and ultimately, larval survival, yolk sac cod fry were stocked at low (10-12 larvae/liter) and moderate (20-25/liter) densities during commercial production.
6. During commercial production, broodstock, gametes, yolk sac fry, larvae and juveniles were rigorously screened for any evidence of disease or the presence of infectious pathogens.
C. Important Results or Findings
By developing protocols to measure plasma and whole-body cortisol, we are able to assess the physiological response of Atlantic cod in any life stage to potential stressors. Using these assays, we found that corticosteroids are present in cod larvae on the day of hatch and a corticosteroid stress response can be measured within 8 days after hatch.
The physiological effect of acute stressors, including netting, handling, transporting, and grading, on plasma and whole-body cortisol, glucose and osmolality is similar to the response of other teleosts subjected to similar stressors. There were no differences in the corticosteroid stress response among groups acclimated to 20 ppt salinity as compared to controls (34 ppt). A significant increase in survival was not realized in larvae raised at lower densities during commercial production, however, size and condition factor were greater.
No individuals tested positively for any pathogens, including nodavirus.
These results represent the first time physiological stress has been quantified in larval and juvenile cod and allow us to evaluate hatchery practices conducive for promoting maximal growth.
D. Difficulties Encountered
Levels of cortisol in whole body homogenates were generally higher than those measured in plasma, which likely reflects the detection of unidentified corticosteroid(s). While this does not diminish our ability to assess the stress response in cod, comparisons of absolute cortisol levels with other species must be made cautiously.
E. Anticipated Success in Meeting Project Objectives on Schedule
We have achieved a significant number of the project objectives and anticipate success in accomplishing those remaining.
F. Reports, manuscripts, and presentations resulting from the project
Manuscript: King V, W. and D.L. Berlinsky. Whole-body corticosteroid and plasma cortisol concentrations in Atlantic cod following acute stress. Submitted to: Aquaculture Research
II. Tasks and Activities for Next Reporting period
A. Tasks for the next reporting period
Our future work involves preconditioning larvae and juveniles to a greater range of environmental conditions (salinity and temperature) and assessing the responses to common hatchery stressors. Our goal is to identify conditions that can mitigate the response to acute stressors.
B. Brief work plan to accomplish tasks
Juvenile cod will be acclimated to reduced salinity conditions (20, 15, 10 ppt), and temperatures (5 and 10 °C) for up to 48 hrs and then subjected to an acute stressor. Samples will be obtained 1, 24 and 48 hrs following the stress. Plasma or whole-body levels of cortisol, glucose and osmolality will be determined.
C. Anticipated concerns or difficulties
None expected.
III. Expenditures
Expenditures were within the range anticipated for the work accomplished to date.