World Aquaculture 21 explant has intact pinacoderm or sponge skin. Using this method, a dozen partially harvested sponges can produce a hundred explants for farming. However, this process would only be used to supply farm seed stock for the first few years of a commercial sponge farm. Subsequently, new explants would be created from sponges produced on the farm. Farming Method An important step in developing a successful bath sponge aquaculture industry is identifying the optimal farming procedures and methods for local species and conditions. Sponges have been experimentally farmed in the sea for over 100 years, with early culture attempts involving threading sponges onto thin wire line so they hung in mid-water. This method has also been tested successfully using modern materials (plastics) for several Mediterranean species and is employed in Micronesia for small-scale commercial farming. Some sponges, however, become dislodged from a threaded line, possibly because of damage incurred when the line is threaded or unfavorable line material is used, promoting an avoidance response. Farming sponges in mesh bags or panels eliminates these problems for some species. Experiments were conducted at both Queensland locations to identify a method for growing bath sponges successfully under local conditions. Novel and existing methods were tried, such as threaded-line, mesh panels and spikes, each varying in material composition or mesh size. The experimental results from the Palm Islands and Torres Strait were unambiguous. Coscinoderma sp. and R. odorabile grew best when farmed in mesh panels (Figure 3). After one year, mean sponge growth rates were up to three times faster in mesh panels than when other farming methods were used. Sponges farmed in mesh panels also had a good shape, being generally oval or round in appearance. In contrast, sponges farmed on threaded line in these two locations often grew into “doughnut” shapes (Figure 4) which is unlikely to be commercially valued. Survival of Coscinoderma sp. and R. odorabile was also highest in mesh panels, probably because tissue damage was minimal compared to other farming methods so the sponges were less stressed. However, mesh panels were susceptible to biofouling, from algae for example, but regular cleaning and the feeding actions of herbivorous fishes prevented biofouling from becoming a major problem. Another disadvantage of the mesh panels used to date was that they caused surface deformation when sponges grew through the mesh. That issue was being addressed by changing the panel design. Farming Site Farm site selection and identifying favorable environmental conditions that promote growth and survival are also important to promote the commercial success of a bath sponge farm. Sponges are filter feeders and rely greatly on the flow of water to provide food, predominantly bacteria and microalgae. Although sponge growth rates generally increase as water flow rates increase, high water flow from storms or strong currents can damage farmed sponges and reduce survival. A good farming site must, therefore, be situated in a sheltered Fig. 2. Coscinoderma sp. (grey) and R. odorabile (brown) will soon be commercially farmed for their soft, durable fibres. Individuals of both species commonly grow to over 50 cm in size. Fig. 3. Explants of R. odorabile being farmed in a mesh panel. After 1 year, many explants had grown to marketsize.
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