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Measures of egg and larval quality in cod Gadus morhua and the relationship to temporal effects

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Title: Measures of egg and larval quality in cod Gadus morhua and the relationship to temporal effects


1
Measures of egg and larval quality in cod
Gadus morhua and the relationship to temporal
effects
  • Jim Treasurer, Ardtoe Marine Laboratory
  • Chris Cutts, Ardtoe

Bryan Choa and Gordon Bell, IOA Stirling Leslie
Ford, John Clark, Jon Sherwood, Tim Atack, Ardtoe
Supported by Northern Periphery Programme, and HIE
2
Cod farming UK
  • Marine hatcheries
  • Machrihanish Marine Farms
  • Johnson Seafarms, Shetland
  • Viking Ardtoe Marine Laboratory
  • Mannin, Isle of Man
  • Orkney Marine Farms
  • (and Ireland! Carna, Galway)
  • On-growing
  • Johnson Seafarms, Shetland
  • Wester Ross Salmon
  • Finfish, Inverpolly

3
Hatchery
Nursery 2 -5 months
60 plus days
Cod production cycle
On-growing 2 years
Broodstock mature at 2 yrs
Incubation
10 days
4
Egg quality
  • The potential of the egg to produce a viable fry
    (Kjorsvik, 1990)
  • those characteristics of the egg which determine
    its capacity to survive (Bromage, 1995)
  • factors that affect egg quality vary between
    species
  • egg quality variation limits the successful
    production of larval fish
  • several physical, genetic and and chemical
    parameters as well as physiological processes in
    the egg determine the potential to produce viable
    fry

5
Why egg and larval quality are important
  • Relevant for aquaculture as there is a direct
    correlation between egg quality and larval
    survival and performance
  • a rapid and objective assessment of egg quality
    would enhance efficiency of hatchery operations
    and reduce the cost of juvenile production
  • reduce costs by rejecting poor performing batches

6
Key factors affecting egg quality
  • Reviewed by Kjorsvik et al 1990, Bromage 1995,
    Brooks et al 1997
  • Egg over-ripening
  • bacterial colonisation of eggs
  • broodstock stress levels
  • fertilisation practices adopted
  • broodfish nutrition, environmental conditions,
    age, genetic influences

7
Egg quality indicators
  • Should be capable of easy assessment, as soon
    after egg collection as possible
  • fertilisation related indicators
  • physical parameters chorion hardening, shape,
    buoyant
  • morphological and chromosomal parameters
    blastomere development, symmetry
  • ovarian fluid
  • egg size
  • biochemical composition of the eggs

8
Study objectives
  • Can egg parameters be used as an objective and
    reliable predictor of egg quality in cod
  • isolate batch effects and determine their effect
    on egg quality and larval survival to 15 days
    post hatch
  • to standardise egg quality assessment parameters
    in cod

9
Broodstocks and egg collection
10
Parameters measured
  • Eggs
  • viable volume
  • volume egg drop out up to 24 hours
  • egg diameter
  • dry weight
  • wet weight
  • fertilisation rate
  • Larvae
  • hatching success
  • hatch length, weight, condition factor
  • at day 15 post hatch length, weight,
    condition, abnormalities, swimbladder
    inflation
  • survival to day 15 ph

11
Results spawning dynamics
12
Egg production on time
Standardised egg production figures by
dividing egg P/day by female broodstock
biomass Significant relationship P0, F4.1)
between daily egg P (Batch) size and date. As
season progressed batch sizes smaller
13
Proportion of floating eggs
R20.36 as season progressed floating egg
decreased
14
Egg volume
Volume of sphere 4/3 Pie radius3 Significant
relationship r20.25
15
Relationship of dry to wet weight
P0, r20.37
16
Egg weight on time
Sig 0.02, F2.1
Sig P0.04, F1.9
17
Egg weight on batch weight
18
Non viable egg 24 hrs after egg collection
24 hour non viable egg loss varied from 0 to
73 significant relationship with egg weight
spawned P0.012, r20.26
19
Larval performance
Range in survival rate to day 15 was from 1 to
44 Egg batches with highest survival at time of
maximum egg production
20
Significant relationship between survival and
date of spawning (P0.03, r20.27). Egg batches
spawned later in the spawning season showed
lower survival rates. Other factors examined
swimbladder inflation high, abnormalities low,
condition factor variable.
21
Significant relationship between total fatty acid
content and egg volume and mean dry weight
P0.015, r20.29, and P0.001, r20.40
Cutts, Choa and Bell
22
Investment in major fatty acids
Content of the essential fatty acids arachidonic
acid, EPA and DHA increased in eggs through the
spawning season, reached a peak at maximum egg
production and declined later in the spawning
season Cutts, Choa and Bell
23
Conclusions
  • Egg size, egg volume and egg dry weight decreased
    through the spawning season
  • the weight of viable eggs was related to egg
    batch size
  • decreasing survival of larvae to 15 days post
    hatch as the spawning season progressed
  • egg production increased to a peak around 20th
    batch spawned, thereafter production declined
  • as the egg size deceased through the season,
    survival also decreased
  • Highest survival from egg batches spawned from
    the start of the season to peak production
  • in selecting egg batches, incubate batches up to
    the peak period

24
Cod hatchery manual
  • Broodstock management
  • Diets
  • Egg production
  • Egg collection
  • Egg incubation
  • Live feed production
  • Larval rearing
  • Environmental conditions
  • First feeding
  • Feeding protocols
  • Weaning
  • Juvenile culture
  • Abnormalities
  • Fry transport
  • Diseases
  • List of production protocols

25
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26
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28
Significant relationship between survival and
DHAEPA ratio and total n-3 PUFA total n-6 PUFA
ratio Cutts, Choa and Bell
29
Stocks followed and weights
  • Two groups of cod one, hatchery and one wild, age
    4 years, 2nd time spawners
  • Kept in 5.3 m diameter tanks
  • Water temps 6 to 9oC
  • Water supply 20 to 25 litres/min
  • Fishmeal based sausage diet
  • tank 1 8 females 6 males
  • tank 2 6 females 6 males
  • broodstock spawned naturally (go to slide showing
    egg production and collection)
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