Cage Culture Another growout method is cage culture in estuarine waters. Relatively few companies are using this technique, primarily because of the difficulties in obtaining government approval to establish fish farms in public waters. Cage culture in estuarine or marine waters has advantages over other systems, particularly where large-scale production is envisaged. There are however, problems with bio-fouling of cages and to a lesser extent, predators, which can cause holes in the cage and hence the escape of stock (Schipp, 1996). Predator nets around the cages are recommended (Barlow, 1998). Tank Culture The third method of on-growing barramundi is intensive production in an indoor, controlled environment building, using underground water (i.e. pathogen free) and a high level of recirculation through biological filters. Because of the controlled environment, it allows for year-round production virtually anywhere in Australia where underground water is available. It also avoids the environmental concern associated with release of nutrients to open waterways from pond or cage culture operations (Schipp, 1996). However, capital and operating costs may be higher than for outdoor cage systems (Barlow, 1999). Diet In Australia, farmed barramundi are reared on dry, pelleted diets, in contrast to South-East Asia where they are usually reared on 'trash' fish or in association with a foraging species such as Tilapia spp (Barlow et al., 1996).Weaning fry from live feed to dry crumbles can be commenced with fry as small as 10 mm TL, but much better survival and quicker adaptation onto the dry diets is obtained if weaning is delayed until the fry are at least 15 to 20 mm TL (Barlow et al., 1996). Barramundi are reared on progressively larger pellets as they grow from fingerling to market size. Most farmers prefer to use semi-floating extruded pellets as they float about 20cm from the water surface. Barramundi are reluctant to feed from the water surface or the pond or tank bottom. Diets produced by Australian fish feed manufacturers give good food conversion ratios (FCR) of 1.6 to 1.8:1 under commercial farm conditions (Barlow et al., 1996). Recent research has shown use of high protein (> 55%) and high energy (> 18% fat) diets for juvenile and plate-sized barramundi can greatly improve growth, FCR (< 1.0 in experimental systems) and profitability of barramundi farming. Formulated feeds need to be stored correctly to avoid loss of nutrients, this is particularly important in the tropics where fats will quickly go rancid and vitamins break down if not stored in an air-conditioned room. Pelleted feed should not be stored for extended periods (Schipp, 1996). Informtation courtesy of the WA Department of Fisheries | 