The project aims to investigate the use of duckweed in partitioned recirculation systems to achieve essentially similar objectives to the lotus proposal for Australian aquaculture (above).
This project also intends to investigate other methods currently being developed at BIARC, including biofloc (see Section 12.3.1) and mechanical filtration techniques for water treatment on a pond scale.
It has been shown that duckweed is very effcient in removing ammonia from wastewater in integrated wastewater treatments. The DPI&F is examining its effciency for removing the nutrient from a partitioned aquaculture system (using barramundi as the test species).
This new project was developed with the ABFA and aims to investigate and compare two plant-based partitioned systems and then evaluate their fishcarrying capacity limitations.
This DPI&F-led project has funding support of the Australian Centre for International Agriculture Research (ACIAR) for a period of five years. The project commenced in March 2007, but was delayed by 2007’s extremely cold winter. Consequently, re-stocking was completed in November 2007.
Biotechnology applications:
Advancing puberty in fish:
The time it takes a fish to undergo gonadal development is commercially significant— some species are late-maturing and broodstock require maintenance for many years before any spawning occurs.
Regulation of the time of puberty is also important for reliable hatchery productions—some species do not undergo natural reproductive development in captivity. The exact events that trigger puberty in fish have yet to be established.
Puberty can be defined as the change from a fish that spends all of its energy growing to a fish that spends significant energy on gonadal development. In order to understand the mechanisms regulating the onset of puberty in fish, genes that are involved in the reproductive function of the grey mullet (Mugil cephalus) have been isolated and cloned.
(The mullet is a model species for late-maturing fish.) The DPI&F has isolated and characterised the KiSS1-receptor, also called GPR54, which belongs to the KiSS1 system and is considered the ‘gatekeeper’ of puberty in mammals—and possibly all vertebrates. These findings have paved the way for the development of new hormonal manipulation approaches that have the potential to advance puberty and spawning in fish.
Regulating moulting in crustaceans:
Moulting is an important physiological event in crustaceans. It is essential for metamorphosis (the change from larva to adult), growth and reproduction.
Moulting occurs in cycles and involves shedding a hard exoskeleton to expose a soft new shell, the uptake of water from the crustacean’s immediate surroundings (causing the new exoskeleton to expand) and, finally, the hardening of the new exoskeleton.
It is during the soft shell stage, a very short window of 2–6 hours, that a particularly valuable seafood product—the soft shell crab—can be produced. The moulting process can be affected by a range of environmental cues (such as temperature and photoperiod) and is regulated by a cascade of hormonal signals. In spite of extensive research, there is still no clear understanding of the hormonal processes involved in moult regulation.
The BIARC has adopted two approaches in its study of moulting in blue swimmer crabs (Portunus pelagicus). In the first instance, classical molecular techniques were used to isolate several genes important to the moulting process. In the second instance, a new and powerful technology—the microarray—has been used to comprehensively study gene expression and to discover new genes involved in moult cycle regulation. This second approach enables the examination of thousands of genes simultaneously.
Using microarrays, the expression profiles of genes of interest have been tracked during the entire moult cycle and these profiles have been used to find new, as-yet-undiscovered genes. Of particular interest has been the isolation of genes involved in shell hardening.
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