Growth and Health Issues Although marron have been reported to grow to 2 kg, farmed marron are harvested at much smaller sizes for economic reasons. Depending upon culture conditions, such as water temperature, nutrition and stocking density, marron can grow to between 60 and 150 g within 12 months and between 100 and 300 g within 24 months (Morrissy 1976a, Morrissy et al 1990, Morrissy 1992b). Both the average weight and the individual weights of a pond of marron are highly variable and economically significant as wholesale price generally increases with individual marron size. Serious primary infectious diseases have not been a major problem on marron farms and none pose any threat to consumers. Like all freshwater crayfish, marron can have several species of tiny animals attached to their shell and gills. Two such epibionts are Epistylis and Temnocephala. These cause marketing problems and are symptomatic of poor water quality and growth rates, particularly in unaerated ponds containing excessive organic matter. The protozoan Thelohania (Cotton Tail or Porcelain disease) has been reported in yabbies and gilgies in WA in the late 1990s, and vigilance will be needed to exclude Thelohania from marron farms. The importation of all overseas crayfish species into Australia is prohibited, since they can carry the crayfish plague fungus Aphanomyces astaci (Morrissy 1992a), to which Australian crayfish are likely to be very susceptible. Unauthorised live transfers of Australian freshwater crayfish into Western Australia are prohibited. In the absence of major disease problems in well-designed and managed systems, the biggest threat to the survival of ready-to-harvest marron comes from poor handling and processing techniques. Informtation courtesy of the WA Department of Fisheries |