FURTHER WORK ON THE EFFECTS OF PURGING
Broad Aim: To maximise post purge survival
Specific Objectives:
To extend the objectives in "Purging 01" to determine minimum purging
times for different commercial sizes of redclaw
To determine the subsequent effect on survival of redclaw
subjected to low oxygen and high ammonia levels during purging
To examine those animals that die and those that survive for the
presence of SMV or other factors that may influence their resistance
to purging stress, such as proximity to moult cycle
Need: As production levels increase, more demands will be placed on farm
purging facilities and the minimum time redclaw need to be in the tanks will become critical.
The conditions in the purge tank are known to be an important factor
for post purge survival, but no quantitative acceptable levels have been
established, nor has the benefit of disease free animals been established-
Method:
Purge samples of various commercial size grades of crayfish and examine gut contents at intervals
Subject crayfish to varying degrees of less than ideal conditions and determine acceptable levels
Comparison of least robust animals with survivors by DPI and JCU pathologists
Resources: Purge tanks and crayfish
Outcomes: Additional information to add to the Best Practice manual compiled in "Purging 01"-
Determining the benefit of disease free animals with regard to withstanding purging stress
DELINEATE THE SPRAY PURGING PROCESS
Proponents: QCFA
Broad Aim: To understand the influence of the various purging parameters
to enable the spray purging process to be optimised.
Specific Objectives:
To ascertain the existing level of knowledge.
To further understand the physiology of the purging process.
To delineate the the influence of the various purging parameters during spray purging:
1) Temperate
2) Time
3) Crayfish size
4) Crayfish density
5) Diet
To produce a best practice manual for purging.
Purging of product before sale is now universally practised throughout the
Redclaw industry.
There is little sophistication used with the process with general rules applied with unknown results.
The process consumes a considerable proportion of the farmers' time
and requires a reasonable amount of equipment.
There is the potential to increase farm efficiency and productivity
by optimising the process. Within the industry there is a move
towards puging using spray chambers and pre-cooling before packing,
however there is considerable unresolved conjecture on how this effects
purging.
Methods:
Conduct a literature search and summarise the available knowledge.
Purge samples of crayfish and examine gut contents at various time periods.
Interpret the results and invent a "degree of purging" measure.
Purge test samples of Redclaw under various values of the above conditions.
Analyse the data and translate into a best practice manual.
Resources required:
Crayfish and a refrigerated spray purging chamber.
Laboratory facilities.
Expected Outcomes:
Increased fundimental understanding of the purging process.
An understanding of the influence of purging conditions of Redclaw.
Best practice manual for the live transport of Redclaw.
DELINEATE THE SUBMERGED PURGING PROCESS
Proponents: QCFA
Broad Aim: To understand the influence of the various purging parameters
to enable the submerged purging process to be optimised.
Specific Objectives:
To ascertain the existing level of knowledge.
To further understand the physiology of the purging process.
To delineate the the influence of the various purging parameters during
submerged purging:
1) Temperate
2) Time
3) Crayfish size
4) Crayfish density
5) Diet
To produce a best practice manual for purging.
Purging of product before sale is now universally practised throughout the
Redclaw industry.
There is little sophistication used with the process with general rules
applied with unknown results. The process consumes a considerable
proportion of the farmers' time and requires a reasonable amount of equipment.
There is the potential to increase farm efficiency and productivity by
optimising the process. Within the industry there is a move towards
paging using spray chambers and pre-cooling before packing, however
there is considerable unresolved conjecture on how this effects purging.
Methods:
Conduct a literature search and summarise the available knowledge.
Purge samples of crayfish and examine gut contents at various time periods-
Interpret the results and invent a "degree of purging" measure.
Purge test samples of Redclaw under various values of the above conditions.
Analyse the data and translate into a best practice manual.
Resources required:
Refrigerated tanks and crayfish.
Laboratory facilities.
Expected Outcomes:
Increased fundimental understanding of the purging process.
An understanding of the influence of purging conditions of Redclaw.
Best practice manual for the live transport of Redclaw.
POST HARVEST SURVIVAL
Proponents: QCFA
Broad Aim: To understand the causes for post harvest mortality.
Specific Objectives:
The investigate the possible causes for post harvest mortality.
To produce a best practice manual for post harvest operations.
One of the natural advantages that Redclaw possesses is its ability to
survive out of water for several days. As a result the majority of Redclaw
are transported and sold live. While this greatly simplifies the selling process for the farmer,
it is not always the ideal form for the buyers. For those buyers who
immediately cook the Redclaw, receiving them live is acceptable.
However for those buyers who wish to keep the crayfish alive until presented to the consumer,
Redclaw have proved to be difficult to accomodate.
In contrast to yabbies (cherax albidus and cherax destructor) which can be
stored alive for weeks
in a normal coldroom, Redclaw cannot survive for more than a few days when kept cool,
and a normal cold room is too cold.
Many buyers have attempted to put the live Redclaw after transport into tanks but survival is poor.
Need:
Modem operation of Redclaw farms includes frequent harvesting, sorting and
restocking of the crayfish.
This necessarily includes handling the crayfish out of water for varying periods of time.
There is strong anecdotal evidence that subsequently there is significant mortality in the
restocked ponds. This clearly has major implications on farm profitability but there is little
information available on which to base changes to improve farm practices.
Methods:
Conduct a literature search and summarise the available knowledge.
Remove crayfish from water, hold for time periods then return to water and observe mortality as a function of:
1) Purging technique,
2) Time, temperature and humidity when held out of water.
3) Water conditions when re-immersed.
Analyse dead crayfish to determine the cause of death.
Analyse the data and translate into a best practice manual.
Resources required:
Crayfish from a commercial farm's purging facility.
Environment controlled transport boxes.
Environment controlled tanks or aquaria.
Laboratory facilities.
Expected Outcomes:
Increased fundimental understanding of post-harvest mortality.
An understanding of ways to minimise post harvest mortality.
Best practice manual for the live transport and live storage of Redclaw
