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The impacts of cohort structure on behaviour, growth performance and stress physiology in juvenile barramundi. Digory Hulse Ryan Wilkinson – John Purser. Introduction. Aggressive, cannibalistic species Particularly larval & juvenile Mitigation of cannibalism

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slide1

The impacts of cohort structure on behaviour, growth performance and stress physiology in juvenile barramundi

Digory Hulse

Ryan Wilkinson – John Purser

introduction
Introduction
  • Aggressive, cannibalistic species
    • Particularly larval & juvenile
  • Mitigation of cannibalism
    • Frequent size grading from metamorphosis to 10cm (up to 3 times/week)
    • Ad libitum feeding
  • Highly fecund sequential spawners
    • > million eggs

Picture courtesy Australian Barramundi Farmers Association

industry practice
Industry practice

  • Spawning procedures
    • Wild or domesticated
    • Often 2 females
    • ♀8 – 12 Kg
    • 600,000 eggs/female
    • ♀ induced by hormone injection
    • Placed with 3, up to 10 males
    • Natural spawning follows
    • 95% fertilisation rate
  • Larval rearing
    • 20 - 50% mortality
    • ‘Unknown mortality’
    • How does this range in mortality manifest itself?

x

industry practice1
Industry practice

  • Spawning procedures
    • Wild or domesticated
    • Often 2 females
    • ♀8 – 12 Kg
    • 600,000 eggs/female
    • ♀ induced by hormone injection
    • Placed with 3, up to 10 males
    • Natural spawning follows
    • 95% fertilisation rate
  • Larval rearing
    • 20 - 50% mortality
    • ‘Unknown mortality’
    • How does this range in mortality manifest itself?

x

industry practice2
Industry practice

  • Spawning procedures
    • Wild or domesticated
    • Often 2 females
    • ♀8 – 12 Kg
    • 600,000 eggs/female
    • ♀ induced by hormone injection
    • Placed with 3, up to 10 males
    • Natural spawning follows
    • 95% fertilisation rate
  • Larval rearing
    • 20 - 50% mortality
    • ‘Unknown mortality’
    • How does this range in mortality manifest itself?

x

industry practice3
Industry practice

  • Spawning procedures
    • Wild or domesticated
    • Often 2 females
    • ♀8 – 12 Kg
    • 600,000 eggs/female
    • ♀ induced by hormone injection
    • Placed with 3, up to 10 males
    • Natural spawning follows
    • 95% fertilisation rate
  • Larval rearing
    • 20 - 50% mortality
    • ‘Unknown mortality’
    • How does this range in mortality manifest itself?

x

kin non kin familiar non familiar

Kin & non-kin; familiar & non-familiar

x

x

  • Between hatcheries:
    • Non-familiar and non-kin (siblings)
  • Within hatchery:
    • Familiar and kin
    • Familiar and non kin
    • Non familiar and kin
    • Non familiar and non kin

B

A

the effects of cohort structure in other teleosts
The effects of cohort structure in other teleosts
  • Increased
    • Aggression
    • Territory defence
    • SMR
    • Growth

depensation

    • FCR
    • Damage
  • Decreased
    • SGR
    • Condition factor
relevant barramundi research to date
Relevant barramundi research to date
  • Limited published material
    • Morphometrics of cannibalism (Parazo et al., 1991)
      • Body depth prey vs. mouth gape predator
      • Mouth gape relative to total length
      • 33% variation = lunch
    • Mitigation of cannibalism (Qin, 2004; Applebaum & Arockiaraj 2010)
      • Light intensity
      • Refuges
      • Unfeasible for commercial aquaculture
slide10
Aims

1. To evaluate whether inserting passive implant transponder (PIT) tags into the peritoneal cavities of 70 mm long juvenile barramundi impacts growth performance or survival?

4. To examine whether the physiological stress response is linked to population, rates of interaction, damage, growth or growth variability.

5. To make an assessment of the response of juvenile barramundi to olfactory cues of familiar and unfamiliar conspecifics

2. To observe wether barramundi from different hatcheries display different:

AND

3. To examine whether mixing populations of fish from different hatcheries impacts on:

  • Rates of interaction & subsequent body damage
  • Growth performance
  • Feed utilisation efficiency
  • Growth variability
  • Propensity for cannibalism
experimental design

Experimental Design

Impact of cohort structure on behaviour & growth performance

Acclimate fish to 12‰ at 30ºC

x

x

    • Fish sourced from 2 hatcheries, H1 and H2.
    • PIT tag 54 fish (8.6 ± 0.21g) from each hatchery
    • 3 ‘groups’ of fish (n=36/group), H1, H2 and MIX
    • 12 fish per tank
    • Triplicate tanks in a RAS
    • Fed to satiation twice daily for 6 weeks
  • Data collection
    • Daily feed intake & behaviour
    • T0,1,2,3,4,5,6: weight, length, damage
    • T6: cortisol, glucose

Distribute into experimental system

Anaesthetise, & PIT tag

Twice daily feed

15 minute interaction video

H1

H2

MIX

Weekly length, weight damage

Endocrine response @ termination

data analysis
Data analysis
  • All statistical analyses were carried out using either SPSS or SigmaPlot
results behaviour
Results – Behaviour

Daily mean interactions in 4 categories.

  • Interactions recorded for 15 mins per day in 4 categories: Chasing, body contact, anterior contact, and fighting.
  • Chase: 5.9 fold in H1
  • Body: 6.9 fold in H1
  • Anterior: 4.6 fold in H1
  • Fight: 4.9 fold in H1
results behaviour1
Results – Behaviour

Weekly mean chase events ± standard deviation

  • Increase in chase events over time for H1. The trend for H2 was reducing though no differences were observed
  • Positive correlations observed between rate of chasing and increase in damage (r=0.0875) and % size difference (r = 0.685) for H1 population
results behaviour2
Results –Behaviour

Weekly mean body contact events ± standard deviation

  • No differences observed in rates of body contact events over time for either population
  • Positive correlation observed between rate of body contact events and increase in damage (r=0.764) for H1 population.
results behaviour3
Results – Behaviour

Weekly mean anterior contact events ± standard deviation

  • More anterior contact events in H1 than in H2
  • H1 showed no differences over time in rates of anterior contact events.
  • H2 showed a reduction over time in anterior contact events
results behaviour4
Results – Behaviour

Weekly mean fight events ± standard deviation

  • More fight events in H1 than in H2
  • H1 showed no differences over time in rates of fight events.
  • H2 showed a reduction over time in fight events
results behaviour5
Results – Behaviour

Weekly mean total interactions ± standard deviation

  • Increase in total rate of interactions over time in H1 and corresponding decrease in H2
  • Negative correlations observed between rate of interactions for all categories and % size difference for H2 population.
  • Other –ve correlations corresponding to growth common in H2.

Comprising 4 categories: Chase, body contact, anterior contact, fighting

results damage
Results – Damage

Mean damage ± standard error

  • Damage increased over time for both treatments
  • No differences in damage between populations was observed.

Damage was calculated based on a score combining incidence and severity with a range from 1 – 5.

results growth performance
Results – Growth performance

Feed intake, FCR and SGR ± standard error

  • The total final biomass of each population was 1632 g for H1 and 1649 g for H2
  • No differences observed between populations for feed intake, feed conversion or growth rate.

Total feed: H1, 365.7 g; H2, 373.8 g

Overall FCR: H1, 0.85; H2, 0.87

Overall SGR: H1, 4.0%; H2, 3.9%

results growth variability
Results – Growth variability

Mean maximum within tank length difference ± standard deviation

??

No difference in total interactions

Cannibalism possible at 33%

  • Difference in length (%) between the largest and smallest fish appears to be a better indicator (in H1) of increased interaction
  • No cannibalism was observed.
results mix population
Results – MIX population

Daily mean total interactions

  • More interactions. min-1 in H1 than H2
  • Mixing populations H1 and H2 to form MIX
  • No differences in rates of total interactions.min-1 between H1 and MIX or H2 and MIX

No differences were observed over the 6 weeks for any of the evaluated parameters either between MIX and H1 or H2, OR the constituent groups within MIX, ie when the H1 fish from MIX were compared to the H2 fish from MIX.

conclusions
Conclusions:
  • Juvenile barramundi are good candidates for studies involving PIT tag implants
  • Rates of aggressive interaction varied between source hatcheries but no difference was observed between the MIX population and source hatcheries. No differences in damage were observed.
  • There were no differences in growth performance between populations
  • There were no differences in FCR between populations
  • Variation in length was higher in the behaviourally recorded tanks of H1 than H2
  • Cannibalism was not observed in any population despite previously published differences in length suggesting it was possible.
future research
Future research:
  • The impact of diet and feeding regime on rates of short and long term behavioural interactions and stress physiology
  • An assessment of the variability of aggressive interactions between sibling groups
  • An assessment of the variability of aggressive interactions within sibling groups.
  • Further studies on SMR of dominant and subordinate individuals as well as comparative studies of SMR on a population level.