Non Technical Summary

The overall aim of this project was to determine the essential nutrients for prawns, silver perch and barramundi that would enable the efficient formulation of feeds to suit the economic constraints of farming those species. The issues that confront the feed formulator are the cost of the feed, how this can be balanced against the need to maintain a high growth rate of the target species and maintaining a favourable feed conversion efficiency. In addition, there is an increasing need to minimise the nutrient waste entering waterways from aquaculture operations - the feed is the greatest source of waste nutrients in an aquaculture operation.

The responses of prawns, silver perch and barramundi to different levels of digestible protein and energy were studied. Results did not allow the estimation of optimal contents for prawns although they did show that prawns use protein more efficiently as an energy source than carbohydrate. For silver perch, optimal contents for best protein utilisation were estimated. From a practical perspective, silver perch farmers wishing to get the greatest growth are advised to feed fish as much as they can eat if they are using low protein diets (e.g. less than 30% protein). If feeding must be restricted (e.g. to prevent poor water quality), then a higher protein diet is advised. Optimal contents for barramundi were also estimated. Economic modelling for barramundi provides a clear incentive for barramundi farmers to feed fish on diets with at least 50-55% protein and 18-20% fat.

Cholesterol is an essential but expensive nutrient for prawns and must be provided in the feed. Results showed the recommended level of cholesterol in prawn feeds is higher than that actually required, allowing for a significant reduction in the amount of supplementary cholesterol used. Ingredients such as fishmeal, and other marine ingredients that are typically used in prawn feeds, can provide all the necessary cholesterol without need for any supplementation.

A study was done to define the dietary requirements of silver perch for two essential fatty acids. The results demonstrated that diets can be formulated without fishoil, but the best weight gain is achieved when the diet contains a mixture of different fats, including some of the type of fat found in marine products such as fishmeal or fish oil.

A study was conducted to evaluate the nutritional value of peanut meal, canola meal, meat meal and dehulled field peas in the diet of juvenile silver perch which estimated the maximum content of these ingredients that can be included before performance is reduced.

In combination with results from the other two projects in the Aquaculture Diet development Subprogram, these results have led to better, more cost-effective diets for prawns, silver perch and barramundi.