Aquaculture

Question 0

What problems are associated with fishing?

Answer 0

Limited tradition of mass fish rearing - progress due to trial and error
Farmers not able to easily monitor food intake, individual health, social interactions (little “common sense” knowledge through experience)

Question 1

Why had there been a rapid increase in salmon fishing over the last 20 years?

Answer 1

Decrease in traditional fisheries, improvements in husbandry and disease control

Question 2

What is the optimal foraging theory?

Answer 2

Handelability of prey influences profitability
Eg. Wanowski 1981- smaller the prey, more easily captured and ingested, bigger the prey more likely to be rejected and can’t be captured. Smaller prey less profitable so also less likely to be captured.

Question 3

How may the appearance of food affect feeding?

Answer 3

Clarke and sutterlin 1985 - if exposed to specific colour food will show a preference for that colour
If naive more likely to go for red food
If fed separate colours, different fish will focus on different colour -> decreased confusion effect

Question 4

What is the confusion effect?

Answer 4

Gillet 1979 and treharne + foster 1980 - too many prey -> increased time to catch any one individual. Demonstrated in lizard and humans.

Question 5

How may operant learning be used in fish farms?

Answer 5

Tipping 1986 - On demand feeders minimise wastage, lowers feed conversion rates, improve growth rates and group fish making them easier to catch.

Question 6

What occurs wrt growth rates of juvenile salmon?

Answer 6

Metcalfe 1989 - Split into a bimodal population - socially subordinate and dominant groups. Individual life history is largely environmentally determined.

Question 7

How does dominance status affect growth and health in fish?

Answer 7

Sight of dom -> stress, v feeding behaviour

Subs have ^ fin damage

Question 8

How can aggression and dominance problems be minimised?

Answer 8

Increase available space
Sort into sizes? Though this causes stress in itself
V monopolisation of resources
Spread feeding out

Question 9

Why is is aggression affected genetically?

Answer 9

Ferguson and Noakes 1982 - Stronger maternal influence than paternal

Question 10

How does stocking density affect dominance?

Answer 10

Very high stocking density -> NO social dominance hierarchy

Question 11

How does size-grading of fish occour?

Answer 11

Fish sieved into different sized categories - removal of large fish allows smaller ones to grow faster
Problems
- same sized fish compete for same optimal sided food particles
- big fish grow slower as hierarchies emerge in all groups - total biomass unchanged
- sieving procedure time consuming and stressful

Question 12

How does frequency of feeding affect dominance?

Answer 12

Jobling 1983 - Increased frequency feeding decreases dominance

Question 13

How may tank design differ?

Answer 13

Conventional
- square
- water enters from side and spiral s to centre drain
- local eddies and currents form around drain and corners
- food unevenly distributed and growth rates vary
Thorpe and Wankowski tank
- circular
- water enters at centre and flows radially outward
- ring of inward facing food forms, food spread evenly
- but harder to clean

Question 14

Why would rewarding and releasing fish be done?

Answer 14

Enhancing stock populations
Stocking
Ranching -90% of fry would normally die

Question 15

What are the problems associated with rearing and releasing fish?

Answer 15

Catching food - “holding station”

Predators

Question 16

How may “training” fish affect their release?

Answer 16

> Creswell&williams 1983- If trained can spend more time upstream where food is better
Of untrained -> fat and lazy, end up downstream poor food supply
predator avoidance training
Chinook and coho salmon fry exposed to predator fish model paired with electric shock -> some fish learn aversion within a few days
Trained fish had 50% mortality of untrained
Previous experience of a predator alone increased survival of a future predator encounter

Question 17

How may recapture of fish be enhanced?

Answer 17

Navigational clues and imprinting
Premigratory salmon salmon exposed to strong smelling chemical (morpholine)
When reintroduced, chemical added to creek entrance where recapture was occouring - 7x as many prepared fish from multiple release sites recaptured compared to non-prepared ones.