A component of ACIAR project FIS 2001/075 ‘Sustainable aquaculture development in the Pacific Islands region and northern Australia’ is the transfer of sea cucumber production technology to Australia.
The project focused on NFC staff training in the production of sandfish (Holothuria scabra) and assessed the use of this species as a bioremediator in prawn culture.
Trials carried out on prawn farms indicated that sandfish were not suitable for co-culture—a result supported by similar research overseas.
There may, however, be potential to grow hatcheryproduced sandfish in prawn ponds and produce commercial-sized animals using nutrients already in the sediments.
Juvenile sandfish produced at NFC in late 2006 were stocked into a prawn pond in Ayr in March 2007. The growout trial will conclude in mid-2008. Survival, growth and value of the sandfish will indicate whether this species has any potential as a commercial commodity in Queensland.
Crabs:
In June 2008 the crab aquaculture team at BIARC will complete a collaborative project with researchers from Queensland University of Technology (QUT).
This two-year ACIAR project examines the feasibility of developing low cost feeds for mud crabs (Scylla spp.) in South-East Asia.
Institutions in Vietnam and Indonesia have been working on corresponding diets for S. paramamosain using locally sourced ingredients, while DPI&F have been investigating Scylla serrata.
A PhD student from Vietnam is completing a comparative study of carbohydrate utilisation and feeding responses of both mud crab species.
A review of the project last year recommended that further attempts to maximise growth of crabs in laboratory experiments should be equivalent to the growth of crabs free in ponds (which always have food available).
This year both the timing and amount of feed delivered to seventh instar mud crab juveniles were studied.
This work required the development of an innovative self-cleaning, container-based laboratory culture system and an automatic feeder that enabled the delivery of specific rations to 256 individual crabs on a programmed schedule.
Expressions of interest have been called for further commercial development of the laboratory growout system. To reduce handling of crabs in experiments, the development of a wireless infrared video system for photographing crabs in their darkened containers and estimating their size using image analysis was required.
Crabs were fed one of three types of diet—fresh (squid, mussels etc), a commercial prawn diet (Turbo, CP) and a research pellet based on the ACIAR rock lobster diet. These diets were fed at 5–20% body weight per day, divided into two or three meals per day.
The high ration treatments were used because of evidence that early crab instars may be capable of eating more than 5% body weight per day.
A workshop was held on 4 December and 5 December to discuss preliminary results from the feeding experiment and to plan future crab research.
Preliminary statistics show that growth of crabs fed different types of diet was not significantly different (though, as might be expected, the average size of ‘fresh diet’ crabs was the highest).
Increasing the ration supplied to juvenile crabs above 5% did not increase growth rate—the average growth rate did not even increase progressively.
It may be that dietary effect is greatest in very early instars (e.g. fourth instar)—the size that would normally be grown communally in nursery ponds— but by the time crabs are harvested for experiments their moult increment and food consumption has probably settled down to approach sub-adult growth and consumption patterns.
Similarly, splitting the same ration into three meals (adding a midnight feed) showed no significant size improvement when compared with crabs fed twice a day (morning and afternoon), though perhaps an increase in statistical power would render significant the slightly higher mean for three meals.
It is conceivable that delivering food more frequently in smaller batches would increase growth because the food would be more effciently eaten and less prone to leaching.
Observations are being made on gut-filling and clearance times to verify this. This year the DPI&F also discussed R&D issues with both Queensland soft-shell blue swimmer crab farms (in Brisbane and Bundaberg).
For example, increased experience with holding crabs indoors has raised questions about stress imposed by intensive holding systems on the condition and moulting of crabs.
Operators of intensive recirculation culture systems know that accumulation and spoilage of uneaten feed and water quality deterioration are undesirable, but subtle, sub-lethal effects involved with moulting crabs in containers remain to be investigated.
In discussions with farmers and DPI&F vets consideration was given to what routine methods of health/condition assessment are available for crabs in farms or feeding trials, and also what opportunities exist for postgraduate student research into more specific stress tests.
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