Carapace mineralization and hepatopancreatic indices in natural and cultured populations of marron (Cherax tenuimanus) in Western Australia

Abstract

Marron (Cherax tenuimanus) were sampled from three wild populations in south-western Western Australia (Warren River, Donnelly River and Gardner River) and from five farmed populations in south-western, lower-western and central-western Western Australia. Mean calcium concentrations in the carapace were higher in wild populations (from 182320 to 213140 mg kg^-1 dry matter) than in farmed populations (from 141960 to 182090 mg kg^-1). The average calcium concentrations in the carapace were two-thirds those of other freshwater crayfish species. Mean carapace magnesium concentrations varied from 970 to 1880 mg kg^-1 with no evident difference between wild and farmed populations. The proportion of calcium and magnesium in carapace inorganic matter varied from 54% to 78% and from 0·32% to 0·75%, respectively, being higher in the wild than in the farmed populations. With minor exceptions, carapace mineralization parameters correlated positively with calcium, magnesium and hardness of the water, and negatively with water pH. The wet hepatosomatic index, 4·5–6·0%, and the dry hepatosomatic index, 1·3–2·5%, were both higher in the farmed than in the wild populations, indicating better condition in the farmed marron. Hepatopancreas moisture concentration varied inversely with hepatosomatic index, ranging from 56·2% to 71·9%.