Reducing the dependency of aquaculture on fishmeal is key for sustainable development of the industry. Feeds for most omnivorous fish species such as tilapia, carp, catfish and milkfish are now devoid of fishmeal. However, reduction of fisheries products in the diets of carnivorous species still poses a huge challenge. Feed accounts for 50% of the total operational costs in aquaculture with fishmeal as the main protein source (average inclusion level of 24% in the diets) and thus the feed industry is beset with increasing costs, shortages and a conflict with human consumption. This has led to the exploration of the use of unconventional ingredients in fish feeds.

Soybean meal is the most available and commonly used plant ingredient in aquaculture. Fishmeal replacement by oilseeds is only limited to 20-40% and a mean incorporation of 10-20% for carnivorous fish species. Oilseeds are characterised to be deficient with EAA, particularly methionine and lysine. It also contains several anti nutritional factors that can be inactivated by heat processing or solvent extraction. Palatability is compromised when plant ingredients are incorporated in the diets of the fish, thus the addition of feeding stimulants is needed.

Pea seed meal, Pisum sativum and lupin, Lupinus spp. and other beans can contribute to the substitution of fishmeal. However, due to the minimal protein content (22 – 30%) their incorporation has been limited due to the presence of anti-nutritional factors, poor essential amino acid profile, presence of non-starch polysaccharides and a high starch content, which should be taken into consideration when formulating a diet. They can replace fishmeal at a level of 10-30%.

Cereals including maize, rice and wheat are incorporated into diets mainly as an energy source. They are low in protein (8-12%) but a rich source of carbohydrates in the form of starch (about 60%). Cereal incorporation in the diets of carnivorous fish is limited to around 10-20% which provides 5% of the dietary protein. They are deficient in essential amino acids, especially lysine.

Leucaena leaf (ipil-ipil leaf meal), which has an analysed crude protein of around 34.38%, can be supplemented in the diets of tilapia. However, this plant protein source contains mimosine and tannin that are toxic that can affect the digestive process of the fish and eventually lead to poor fish growth.

Groundnut cake, Arachis hypogaea which contains around 31.6% of crude protein, is an alternative protein source which is highly palatable and has an acceptable odor. It has better binding properties than soybean. In spite of its positive characteristics, it is deficient in some essential amino acids (methionine and lysine) and can be contaminated with aflatoxin. Research suggests that groundnut cake can replace around 10% of fish meal in the diets of H. longifilis.

The sweet potato, Ipomoea batatas is an important food crops in tropical areas. The leaves of this plant have been used as a cheap protein source in ruminant feeds. The leaf meal has a protein content between 26-33% and a good amino acid, mineral and vitamin profile. However, it contains anti-nutritional factors that can significantly affect fish growth. Tilapia growth trials have suggested up to 15% inclusion level can be achieved in tilapia diets.

The identification and removal of anti nutritional factors through heat treatment has improved the potential of taro, Colocasia esculenta, as a protein ingredient in fish feeds. Taro leaves have a high amount of protein (31.5%) and a high level of vitamins and minerals which are needed in fish feed formulation. Growth experiment has indicated that a complete replacement of fish meal with taro can be achieved in the diets of tilapia cultured in ponds with high natural productivity.

Harvested duckweed, Lemna spp. plants contain up to 43% protein on a dry weight basis and may be utilised without further processing as a complete food for fish. The amino acid profile of duckweed is relatively good compared to most plant protein sources and it contains high concentrations of trace minerals. Studies have indicated that tilapia fed with duckweed at a feeding rate of up to 30 g dry matter / kg resulted in a higher survival rate and weight gain.

Coconut meal, (copra), Cocos nucifera is made from the process by-product of coconut oil extraction. It contains approximately 22% crude protein. Copra contains no known anti nutritional factors and has a high protein digestibility. However, relative to fishmeal and soybean meal it is deficient in all the essential amino acids required by fishes. Nevertheless, copra is a useful diet ingredient in areas where it is locally available in quantity.

The leaves of water hyacinth Eichhrornia crassipes contain 20% protein and relative to other plants its essential amino acid profile is relatively balanced. However, it has a high fiber content which limits utilisation of this ingredient. Reports have suggested that processing the water hyacinth as concentrates can improve its nutrient profile and can be fed to white shrimp, Litopenaeus vannamei at 25% inclusion level.

Rendered protein or animal by-products, which are comprised of meat meal, poultry meal, meat and bone meal, feather meal and blood meal have a high potential to be an alternative to fishmeal. However, these types of ingredients are heterogenous in nutrient profile, limiting with essential amino acids and prone to bacterial contamination. Protein content ranges from 50-80% and can replace fish meal at a level of 20-40%. These types of ingredients have a good palatability and do not contain anti-nutritional factors. However, they contain high levels of ash and saturated lipid. High inclusion levelsof animal by-product meal in fish feed can cause excess dietary phosphorus which is harmful to the environment and has a deleterious effect on the nutrition and health of the fish.

Shrimp by-product (heads and shells) are produced in large quantities from the processing plants and are commonly used as ingredient in shrimp diets. Head meal, processing residues and waste from shrimp by-products has an average crude protein of 40%. Studies have indicated that L. vannamei growth and survival was significantly improved when shrimp by-product was included in the feeds of up to 18% level. Fish growth experiments with humpback grouper suggested that with the increase of shrimp head meal inclusion in the diets, growth and feed efficiency was adversely affected. High chitin and ash content of shrimp head meal is the main constraint in the performance parameters of fish fed the experimental diets. The study suggests a maximum of 10% shrimp head meal can be included in the diet of the fish.

By-products from the fish processing industry (i.e. milkfish and tuna) can be utilised as an ingredient in fish feeds. On average, derivatives from fish processing have a crude protein of 60% and several essential amino acids are not limiting. Research trials have shown that these ingredients have performed well when fed to grouper, Epinephelus coioides and red sea bream, Pagrus major at an inclusion level of up to 25%. However, product obtained from the processing plants is not homogeneous and freshness cannot be assured.

These alternative and locally available ingredients have been widely used in different countries. Several constraints and gaps in promoting these types of ingredients occur, however, strategies are being implemented to address these limitations.

Most of the alternative nutrient ingredients are characterised to be inferior in protein content, with unbalanced amino acid profiles and the presence of anti nutritional factors. Several studies have indicated that processing these ingredients into concentrates, isolates, hydrolysates and fractionated peptides can improve their nutrient profiles. Processed plant ingredients, when added in the diets of the fish, have resulted to an improved growth, feed efficiency and palatability.

Utilisation of fish processing waste should be researched and promoted. This ingredient has been characterised to have similar nutrient value and volume to fish meals and oils sourced from the wild. The use of fish processing waste to produce fish meal and fish oil can make aquaculture a net producer of fish meal and oil. Studies suggested that further processing these ingredients into hydrolysates can resulted to an improved feed efficiency and growth rate.

Scientific information on feed ingredients, fish nutritional requirements and the interaction between the fish and the diet should be intensively studied. Combination of two or more alternative ingredient should be encouraged in order to create an optimised and cost efficient diet for the industry.

Another approach to minimise utilisation of fish meal is to promote the culture of fish species belonging to lower trophic levels. Herbivorous and omnivorous fish require minimal protein in their diet, thus reducing the fish meal requirement in the diet formulation.

Nutritional compounds found in fish meal and fish oil provide significant human health benefits. Fish fed on alternative feeds must continue to provide these health benefits to consumers. The methods adopted to address fatty acid modification in fish fed alternative nutrient ingredients include (i) the implementation of new n-3 HUFA rich alternative lipid sources, (ii) the restoration of an optimal fatty acid profile with a finishing diet following a vegetable oil grow-out diet, (iii) the use of genetically modified n-3 HUFA rich grain crops and (iv) the farming of transgenic fish with superior n-3 HUFA biosynthetic capabilities.

Current facts and figures have indicated that the use of alternative nutrient ingredients in feed aquaculture is the way forward.

Traditional fish meal and fish oil ingredients are not nutritionally required for farmed fish to grow. Nutrients (amino acids, vitamins, minerals, and fatty acids) are required but they can be obtained from sources other than fish meal and fish oil. Combining alternative nutrient ingredients to get the same balance is possible, but will require intensive research before its application in the aquaculture industry.

Feed companies making diets for carnivorous fish and shrimp have reduced their use on fish meal and fish oil. The use of published scientific research led to cost-effective substitution using alternative ingredients, which reduced feed costs. The ratio of fish in to fish out has been reduced from 3-4:1 to an average of 1.5:1 for major aquaculture species due to increased use of protein and oils in diets from non-marine sources.

In conclusion, four key points are suggested to create a cost effective feed in aquaculture:

• Reduce the level of fish meal and fish oil in the diet of fish.
• Choose aquaculture species which require low protein and lipid in their diet, preferably herbivorous fish.
• Formulate feeds which are environmentally friendly.
• Formulate feeds with ingredients that are sustainable.