Replacing fishmeal in aquaculture diets

• Department of Fisheries, Thailand
• Department of Fisheries, Thailand

Demand for fish in South and Southeast Asia is expected to escalate by about 5 million tonnes by the year 2000. Production from capture fisheries is static or declining, and production increases will need to come from aquaculture.

Global aquaculture production has increased by about 50% from 1986 yields to an estimated 18.2 million tonnes in 1992 with about 80% of this production in Asia. One of the main constraints on increasing aquaculture production, is the development of cost-effective feeds and feeding strategies.

The protein source of choice for most fish and crustaceans is fishmeal or 'trash fish' (small fish forming the low-value component of commercial catches). However, supplies are declining and prices are increasing. There is also an increasing conflict between use of trash fish/fishmeal for aquaculture, or for human consumption (particularly for low-income indigenous people). The replacement of fishmeal in aquaculture diets is a major international research priority.

The objective of this project, which will involve collaboration between Australia, and Thailand is to develop cost-effective diets for aquaculture species in Australia and Thailand to replace fishmeal and trash fish. A wide range of alternative feed ingredients will be critically evaluated and the digestibility of these ingredients to target aquaculture species will be assessed. The primary target species is the omnivorous silver perch (Bidyanus bidyanus) in Australia and the hybrid catfish (Clarius macrocephalus x C. gariepinus) in Thailand. The secondary target species are carnivorous barramundi (Lates calcarifer) and snapper (Pagrus auratus) in Australia, and carnivorous barramundi in Thailand.

Researchers in both Thailand and Australia will determine the full chemical composition of currently used feeds using standardised methods. Data will be provided through agriculture departments, regional fisheries offices and feed manufacturing companies.

Experiments will be conducted initially in Australia and then in Thailand to assess the digestibility of ingredients. Scientists will measure the amount of each nutrient ingested and subtract the amount excreted in the faeces. Methodology currently in use at NSW Fisheries in Australia involving faecal collection by settlement will be used initially, but will be validated against other methods, e.g. faecal stripping.

Scientists will conduct laboratory feeding studies using graded levels of different ingredients testing the most promising ingredients in larger pond trials. Nutritional deficiencies, and methods to overcome them including the addition of vitamins or minerals will become apparent during growth studies.

To mimimise the amount of protein in the form of fishmeal or trash fish in feeds (and hence cost), the optimum balance between protein, fats and carbohydrate in the diet will be assessed. Researchers will also evaluate the use of alternative protein ingredients for hybrid catfish and silver perch with commercially available synthetic amino acid supplements if necessary.