Effect of dietary protein and lipid source on the growth, survival, condition indices, and body composition of marron, Cherax tenuimanus (Smith)

A trial was conducted in 12 purpose-built, commercial, drainable, earthen ponds to evaluate the effect of fish and plant protein and lipid source on the growth, condition indices, and body composition of marron (Cherax tenuimanus). Juvenile marron (1.3±0.28 S.E. g) at the stocking densities of three per square meter were fed for a period of 1 year with four different formulated isoenergetic practical diets (D₁, D₂, D₃, and D₄). Three of the test diets (D₁, D₂, and D₃) were isonitrogenous whereas the fourth test diet (D₄) was protein-free. Protein and lipid sources in D₁ were from Lupin (Lupinus albus) whereas protein and lipid sources in D₂ and D₃ were from fish meal. Fish oil (3.5%) was added to D₁, D₃, and D₄ whereas sunflower oil was added to D₂ and D₄ in order to make them isoenergetic. The four test diets were randomly allocated to three replicate ponds.

The lack of protein in D₄ did not significantly influence (P>0.05) the mean final weight and specific growth rate of marron. Survival was low in all ponds (13.82–34.66%) but feeding with D₄ resulted in a significantly (P<0.05) higher survival than marron fed with D₁ and D₂. Feeding a diet containing a combination of fish protein and fish oil (D₃) resulted in significantly higher (P<0.05) wet tail muscles-to-body weight ratio than was observed with other diets. Tail muscles protein level of all marron was significantly lower (P<0.05) at the end of the trial than at the beginning. EPA and DHA in hepatopancreas and tail muscles of marron were affected by the four test diets. The inclusion of plant protein in formulated diets had a negative impact on the pond environment due to significantly higher unionised ammonia levels that resulted in lower survival. Juvenile marron fed with a plant protein diet had significantly lower protein levels in their hepatopancreas compared to those fed with diets containing animal protein. Feeding marron with lupin protein source (D₁) and plant oil (D₂) for 1 year did not alter the lipid content of their hepatopancreas. Four test diets had no influence on the fat content of marron hepatopancreas; however, these test diets significantly reduced the protein content of the tail muscles of marron.

Environmental variables, particularly temperature, nitrogen metabolites, and the natural productivity of the ecosystem, greatly influenced the nutritional requirements of the juvenile marron under culture.