Evaluating options for fishmeal replacement in diets for juvenile barramundi (Lates calcarifer)

Two experiments were conducted to examine critical thresholds to fishmeal inclusion in diets for barramundi and also the suitability of a range of different raw materials as alternative protein sources for this species. The first experiment used two diets formulated to the same digestible protein and energy specifications, which were then used to create a series of blended experimental diets that varied in fishmeal content from 0 to 770 g kg(-1). An additional diet containing sodium sulfamerazine was used as a negative control. Feed intake was unaffected with diets containing as little as 11% fishmeal, although broken-line regression suggests that an inclusion of similar to 150 g kg(-1) fishmeal is a more likely threshold value. In a second experiment, a further series of diets was formulated for juvenile barramundi according to digestible protein and energy specifications predicted by existing bio-energetic models. Each of the test raw materials was substituted for fishmeal at either 200 or 300 g kg(-1) (dependent on formulation or extrusion limitations), and two additional diets were included to examine two practical formulations. A diet with only fishmeal as the protein source was included as a reference. Each diet was produced using an APV19 twin-screw extruder and then vacuum infused with the specified fish oil allocation. Each of the diet pellets produced was also characterized for a range of physical parameters. Fish of an initial weight of 70 +/- 0.6 g fish(-1) were randomly allocated across 24 tanks with three replicates per treatment. After 6 weeks, average weight gain across all treatments was 73 +/- 12.7 g fish(-1) and feed conversion across all treatments averaged 0.94 +/- 0.08 g fish(-1). None of the diets using alternative raw materials had poorer growth or feed conversion than the fishmeal-based reference diet. The inclusion of either the lupin kernel meals or canola meal significantly improved both weight gain and feed conversion compared to the reference diet. The results from this study demonstrate that there is clear potential to replace the fishmeal content of diets for barramundi without loss of fish performance, up to and including diets with as little as 150 g kg(-1) fishmeal inclusion.