Safety and performance of aquaculture fish foods produced from food wastes.

Global demand for aquaculture feed is expected to reach 71 million tonnes by 2020 (more than doubling since 2008). Use of food wastes to produce aquaculture feed can offer economic benefits, ensure performance feeds and maintain food safety / contaminant standards, by using appropriate food waste combinations, accompanying technologies and fish production systems.

Fish feed costs represent more than 50% of total aquaculture costs, and prices have increased considerably: +55% to + 250% for different soybean or grain feed materials from 2000 to 2009.

This review paper summarises results of experiments using comparing different food waste based fish feed materials with commercial fish feeds for several species of freshwater fish cultivated in China, including grass carp (Ctenopharyngodon idella), bighead carp (Hypophthalmichtthys nobilis) and mud carp (Cirrhinus molitorella). Polyculture of different species with different feeding modes in the same pond enables optimisation of use of feed energy content. The use of pig manure to fertilise ponds and promote growth of phytoplankton, consumed by fish, is traditional in China.

Literature studies cited show that wastes from food production or processing industries including poultry, soy sauce rice wine, beer and papaya can be effectively incorporated into fish food pellets. This paper presents results on different feed pellets produced from Hong Kong hotel food wastes (including fruit and vegetable peels and discards, raw and cooked meat and fish, cereal wastes and bones) combined with fishmeal and corn starch. Results show that some fish species prefer plant protein to meat, and that the higher lipid levels in meat wastes hinders fish growth.

Food safety
Results also show that the highest levels of persistent toxic substances are in fish meal (mercury, DDT), but also PAH (poly aromatic hydrocarbons) in bone meal. Analysis indicated that levels found in the flesh of fish fed either food waste derived or commercial fish feed did not show any Life-Time Cancer Risk for consumers. Filter and bottom feeding fish tended to have higher levels of contaminants. The authors recommend to develop food waste based aquaculture feed products not containing fish meals.

Upgrading food waste to high performance fish foods

A range of different technologies for improving aquaculture performance of recycled food waste based fish foods are presented, summarising literature data:

  • Use of enzymes such as bromelain (from pineapples), papain (from papaya), with effectiveness similar to the use of enzymes in livestock feed. These enzymes help hydrolyse feed proteins to smaller peptides, with higher digestibility for fish.
  • Addition (premix) of minerals and vitamins. Studies have shown that not only are vitamins and minerals necessary for fish growth, but also their addition can improve protein digestibility.
  • Probiotics, such as 2% live baker’s yeast (Saccharomyces cerevisiae) which both releases amylase enzymes improving feed digestibility and also attach to fish intestine walls stimulating the immune system and reducing infections.
  • “Prebiotics”, for example inulin (oligosaccharide), mannan-oligosaccharides (glucomannoprotein complex derived from yeast cell walls), fructo-oligosaccharides, galacto-olgosaccharides
  • Chinese medicinal herbs, used to enhance fish immunity to infections, e.g. anthraquinone extract from rhubarb (Rheum rhabarbarum), huanqi (Astragalus radix), goji (Lycium barbarum), Radix scutellaria, Rhizoma copitidis, Herba andrographis, Radix sophorae flavescentis.

The authors conclude that food wastes and food production / processing wastes can be used to produce safe and effective aquaculture fish foods, and that enzymes, probiotics (baker’s yeast) and medicinal herbs can be cost-effective in improving the performance of such aquaculture feeds, both by enhancing feed digestibility for fish and by reducing fish infection risks without antibiotic use.

References
“Recycle food wastes into high quality fish feeds for safe and quality fish production”, Environmental Pollution 2016
http://www.sciencedirect.com/science/article/pii/S0269749116305231

M-H. Wong (1, 2, 3), W-Y. Mo (3), W-M. Choi (3), Z. Cheng (3), Y-B. Man (3). 1 = Key Laboratory for Heavy Metal Pollution Control and Reutilization, School of Environment and Energy, Peking University - Shenzhen Graduate School, Shenzhen, China. 2 = School of Environment, Jinan University, Guangzhou, China. 3 = Consortium on Health, Environment, Education and Research (CHEER), and Department of Science and Environmental Studies, The Education University of Hong Kong, Tai Po, Hong Kong, China or                   

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