Size grading did not enhance growth, survival and production of marron (Cherax tenuimanus) in experimental cages

The necessity for size grading prior to stocking in marron culture is not c lear, In this study, production characteristics of marron of three size-gra ded groups (15.2, 78.3 and 157.6 g) and one mixed group were tested in 274 experimental cages (6 X 3 X 2 m) with six replicates for each treatment. Af ter 258 days, mean weight of small marron in the graded group increased fro m 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 fro m 157.6 to 218.9 g, while the large marron in the mixed group increased fro m 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 mixe d group than in the graded group. Size specific growth rates were size-depe ndent 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). Thesequence of net production of different size d groups was small size (1374 kg/ha) > mixed size (1042 kg/ha) > medium siz e (756 kg/ha) > large size (- 275kg/ha). Marron size grading during growout seems to be an unnecessary operation to improve the growth and survival. ( C) 2001 Elsevier Science B.V. All rights reserved.