Migration 3

Question 1

What hormone controls smolt transformation (the morphological, physiological and behavioural changes that occur in fish as they prepare to move to the sea)?

Answer 1

Thyroid hormone

Question 2

How do salmon prepare for spawning run upriver?

Answer 2

-osmosregulation readjusted to cope with freshwater
-gonads increase in mass (up to 50% body weight)
-stop feeding which mobilises fat reserves

Question 3

After how many years at sea do adult salmon migrate back to their natal river to spawn?

Answer 3

After 2-3 years

Question 4

How do salmon find their way back to their natal stream?

Answer 4

1. Open Sea navigation- from their feeding ground to coast
2. Homing- once at coast locate the exact stream in which they hatched

Question 5

How do salmon use open sea navigation?

Answer 5

• sun position
  -polarised light patterns
  -earth’s magnetic field

Question 6

What are the cues from the earth’s magnetic field?

Answer 6

-Polarity
-Orientation of lines of force including inclination
Intensity of field

Question 6

How does inclination and intensity of force vary?

Answer 6

It varies systematically with latitude

Question 7

What do salmon use to find the location of river/feeding grounds?

Answer 7

They use inclination and intensity as a map

Question 8

What evidence was provided by Putman et al. (2015) to show adults migrated home to spawn using geomagnetic fields?

Answer 8

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)

Question 9

What is the olfactory imprinting hypothesis (Hasler & Wisby, 1951)

Answer 9

-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

Question 10

How was an experiment carried out to show that characteristics of river are learnt and not inherited?

Answer 10

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

Question 11

What are the requirements needed for fish to recognise smell?

Answer 11

• 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

Question 12

What experiment shows that salmons can discriminate between streams as they smell different?

Answer 12

Labatory conditioning experiment

Question 13

What evidence shows that salmon remember odour when they return to stream?

Answer 13

Electrophysiological recordings from the olfactory bulb of captured salmon showed a strong response to waters from the natal stream but not others

Question 14

What is Morpholine?

Answer 14

It is an artificial substance that salmon can detect

Question 15

What treatment conditions were used to show homing to artificial substances as evidence for the olfactory imprinting hypothesis?

Answer 15

1. A smolts: exposed to lake water containing morpholine
2. B (control) smolts: lake water with no additives
   The salmon were then tagged and released into the lake

Question 16

What was the results of the homing to artificial substance experiment?

Answer 16

A morpholine tributary was created
-group A entered the tributary, but group B did not
A had imprinted on morpholine

Question 17

How are morpholine imprinted salmon tracked?

Answer 17

Using ultrasonic transmitters

Question 18

When tracking salmon what occurs in morpholine imprinted fish?

Answer 18

They stopped at the mouth of the stream with morpholine but not at streams without morpholine

Question 19

What happened with the control group?

Answer 19

-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

Question 20

What are the sources of distinctive odours in streams?

Answer 20

-rocks, soil, plants
-pheromones, mucus or faeces from relatives in stream

Question 21

How do experiment show that salmon discriminates against family members based on smell?

Answer 21

• 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

Question 22

What is the sequential imprinting hypothesis?

Answer 22

• 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

Question 23

What does elevated levels of thyroid hormone do?

Answer 23

– Initiates migration downstream, exposing salmon to new
environments which further increases hormone level
– Increases the tendency to learn local odour features by
imprinting

Question 24

What is thyroid hormone induced by?

Answer 24

– developmental processes
– environmental factors
* new environments
* change in water temperature
* change in flow rate
* photoperiod and lunar phase

Question 25

How does thyroid hormone influence
imprinting?

Answer 25

• Influences neurogenesis in the
  olfactory epithelium making the fish more sensitive to odours

Question 26

What are the advantages of anadromous life cycle

Answer 26

Spawning streams:
* protected environment,
* little competition
Sea:
* food for growth to large size