Migration 3 Flashcards
What hormone controls smolt transformation (the morphological, physiological and behavioural changes that occur in fish as they prepare to move to the sea)?
Thyroid hormone
How do salmon prepare for spawning run upriver?
-osmosregulation readjusted to cope with freshwater
-gonads increase in mass (up to 50% body weight)
-stop feeding which mobilises fat reserves
After how many years at sea do adult salmon migrate back to their natal river to spawn?
After 2-3 years
How do salmon find their way back to their natal stream?
- Open Sea navigation- from their feeding ground to coast
- Homing- once at coast locate the exact stream in which they hatched
How do salmon use open sea navigation?
- sun position
-polarised light patterns
-earth’s magnetic field
What are the cues from the earth’s magnetic field?
-Polarity
-Orientation of lines of force including inclination
Intensity of field
How does inclination and intensity of force vary?
It varies systematically with latitude
What do salmon use to find the location of river/feeding grounds?
They use inclination and intensity as a map
What evidence was provided by Putman et al. (2015) to show adults migrated home to spawn using geomagnetic fields?
The route taken by adult pacific salmon returning to Fraser River varies (north or south of Vancouver island) with variation in geomagnetic field (inclination and intensity)
What is the olfactory imprinting hypothesis (Hasler & Wisby, 1951)
-During a sensitive period in the smolt transformation, salmon become imprinted to the smell of their home river and
-use the learnt odour pattern to recognise the river when they return as adults
How was an experiment carried out to show that characteristics of river are learnt and not inherited?
Fish are removed from natal river, tagged and released elsewhere. The return river is noted
-Fish translocated before smolt transformation: return to river of release
-Fish translocated after smolt transformation: return to natal stream
They learned to recognise natal streams at the time of smolt transformation
What are the requirements needed for fish to recognise smell?
- every stream has a characteristic and persistent odour
-salmon discriminate between odours of different streams
-salmon remember the odour when they return after time at sea
What experiment shows that salmons can discriminate between streams as they smell different?
Labatory conditioning experiment
What evidence shows that salmon remember odour when they return to stream?
Electrophysiological recordings from the olfactory bulb of captured salmon showed a strong response to waters from the natal stream but not others
What is Morpholine?
It is an artificial substance that salmon can detect
What treatment conditions were used to show homing to artificial substances as evidence for the olfactory imprinting hypothesis?
- A smolts: exposed to lake water containing morpholine
- B (control) smolts: lake water with no additives
The salmon were then tagged and released into the lake
What was the results of the homing to artificial substance experiment?
A morpholine tributary was created
-group A entered the tributary, but group B did not
A had imprinted on morpholine
How are morpholine imprinted salmon tracked?
Using ultrasonic transmitters
When tracking salmon what occurs in morpholine imprinted fish?
They stopped at the mouth of the stream with morpholine but not at streams without morpholine
What happened with the control group?
-The control group did not stop at either stream mouth
-This showed that the odour of the home river arrests a salmon swimming along the shoreline
What are the sources of distinctive odours in streams?
-rocks, soil, plants
-pheromones, mucus or faeces from relatives in stream
How do experiment show that salmon discriminates against family members based on smell?
- Smolts were released (x) upstream of a hatchery with siblings; smolts went to sea
- Returning adults swam past hatchery effluent (y) to release point (x)
-Smell of relatives less important than other stimuli
What is the sequential imprinting hypothesis?
- A series of odour bouquets characteristic of different parts of the river learnt in sequence as smolts migrate downstream
-A series followed in reverse order as adults return upstream
What does elevated levels of thyroid hormone do?
– Initiates migration downstream, exposing salmon to new
environments which further increases hormone level
– Increases the tendency to learn local odour features by
imprinting
What is thyroid hormone induced by?
– developmental processes
– environmental factors
* new environments
* change in water temperature
* change in flow rate
* photoperiod and lunar phase
How does thyroid hormone influence
imprinting?
- Influences neurogenesis in the
olfactory epithelium making the fish more sensitive to odours
What are the advantages of anadromous life cycle
Spawning streams:
* protected environment,
* little competition
Sea:
* food for growth to large size
