Effects of dietary lipid level and source on growth and proximate composition of juvenile redclaw ( Cherax quadricarinatus) reared under semi-intensive culture conditions

The influence of dietary lipid level on growth, survival, and proximate composition of juvenile redclaw crayfish was evaluated during a 12-week growth trial utilizing semi-intensive culture conditions. Four diets were formulated to be isoenergetic (17.58 kJ g −1) and isonitrogenous (30% crude protein). Three of the diets were designed to contain 4.2% (L4), 8.2% (L8) and 12.3% (L12) lipid in a 1:1 ratio of corn oil/fish oil. A fourth diet was formulated to contain 8.7% (LC8) lipid, with corn oil as lipid supplement. A fifth treatment (UF) was included in which the redclaw were not fed in order to estimate the contribution of primary production. Juvenile redclaw (4.08±0.2 g initial weights) were stocked at a density of 10 per tank in 15, 2.5-m 3 fiberglass tanks with three replicates per treatment. The trial was conducted in an outdoor flow-through water system. The redclaw in the unfed treatment gained 8.3 g whereas redclaw that received a prepared ration gained an average of 31.9 g. Hence, in this experiment natural productivity contributed about 26% of the weight gain of the redclaw maintained in outdoor tanks. Among the fed treatments, there were no significant differences in survival, final weight, growth, or feed utilization. The hepatosomatic index (HI) generally increased with lipid level and was influenced by the sex of the redclaw. Results indicated that in similar culture conditions, diets containing 4% lipid are sufficient for redclaw growth and survival when natural food is present.