Size grading did not enhance growth, survival and production of marron (Cherax tenuimanus) in experimental cages. [Erratum: Aug 1, 2001, v. 199 (3/4), p. 373-374.]
2001
Qin, J.G. | Ingerson, T. | Geddes, M.C. | Kumar, M. | Clarke, S.
The necessity for size grading prior to stocking in marron culture is not clear. In this study, production characteristics of marron of three size-graded groups (15.2, 78.3 and 157.6 g) and one mixed group were tested in 24 experimental cages (6 X 3 X 2 m) with six replicates for each treatment. After 258 days, mean weight of small marron in the graded group increased from 15.2 to 40.1 g, while small marron in the mixed group increased from 14.8 to 46.4 g. Mean weight of medium marron in the graded group increased from 78.3 to 129.5 g, while medium marron in the mixed group increased from 76.7 to 132.6 g. Mean weight of large marron in the graded group increased from 157.6 to 218.9 g, while the large marron in the mixed group increased from 165.3 to 223.7 g. Size grading of marron did not lead to improved growth. Marron survival rate was not improved by grading either. Instead, survival rate of medium and large individuals was significantly greater in the mixed group than in the graded group. Size specific growth rates were size-dependent and small marron grew faster than either medium or large individuals. The sequence of standing biomass of different sized groups at harvest was medium size (3080 kg/ha) > mixed size (2941 kg/ha) > mall size (2482 kg/ha) > large size (2037 kg/ha). The sequence of net production of different sized groups was small size (1374 kg/ha) > mixed size (1042 kg/ha) > medium size (756 kg/ha) > large size (-275kg/ha). Marron size grading during growout seems to be an unnecessary operation to improve the growth and survival.
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