Can fish feed be environmentally sustainable?
What is sustainable fish feed?
Sustainable fish feed is the use of fish feed alternative such as insect protein and plant protein, in place of fishmeal. Conventional fish feed is fishmeal, typically made up of lower value fish such as anchovies, sardines, and trash fish. Trash fish is generally considered as inedible or having no food value for human consumption. From 1995 to 2019, salmonid fish feed has become more sustainable as its fishmeal component has reduced from ~53% to 27%. Its fish oil component has also reduced from ~31% to 15% fish oil (the remainder 15% is plant oil replacement). Its alternative protein (insect and/or plant based) has grown from ~16% to 43%. As a result in places like Norway, its total dietary composition of farmed fish relying on fishmeal has dropped by a whopping 60%, from 90 to 30% between 1990 and 2013[i]. Such an exemplary feat is not widely practised elsewhere nor all sub-sectors of aquaculture.
What are the incentives to transition from fishmeal to sustainable fish feed?
Fish meal production is a significant contributor of over-fishing. 61%% of the world’s marine fish stocks are now fully exploited, and 29% of the remainder has been over-fished or depleted[ii]. As a result, the global fishmeal output has remained at 6 to 7 million metric tons per annum for the last 20 years. Due to increase demand, the price of fishmeal has gone from USD$340 per tonne in 1999 to USD$1500 per tonne in 2019[iii]. This represents an average of 8% price increase with each subsequent passing year, and by 2030, it will be approximately USD$3800 per tonne.
Aquaculture is a growing industry demanding ever more fish feed. In the early 2010s, aquaculture output has already exceeded wild fishery output. It is urgent to make animal protein affordable as human population continues to grow and poverty level continues to decrease globally. Over three billion people around the world depend on fish for at least 20% of their protein intake and approximately 20 kg of fish is consumed per capita per annum[iv]. These numbers are only going to increase, driving up demand for fish feed whilst fishmeal supply is and will inevitably remain constant or become depleted.
What are the obstacles in transitioning to sustainable fish feed?
Manufacturing sustainable fish feed typically means replacement of fishmeal with insect or plant protein derivatives which poses a few problems:
1) Of the ten essential amino acids required by fish as recommended by FAO[v], methionine is often deficient in most of the sustainable alternatives. Lysine is often the second most relevant deficiency especially if alternative protein source is derived from palm kernel cake or soy gluten meal.
2) Taurine is an organic compound that is widely distributed in animal tissues but absent in plant based protein. While not referred to as one of the essential amino acids, taurine has recently been identified as being important to fish[vi]. Fish has two ways to meet its taurine requirement, either by consuming other animal protein or by being internally synthesised from methionine and cysteine metabolism. Plant protein can neither provide taurine directly to fish nor enable fish to self-synthesise due to aforementioned methionine deficiency.
3) Deficiency in omega-3 fatty acids which are eicosapentaenoic acid and docosahexaenoic acid. These omega-3 fatty acids come from micro-algae which are gradually concentrated by fish from lower trophic level to higher trophic level through predation. Terrestrial plants and insect lack in these fatty acids. While micro-algae aquaculture can produces these fatty acids, they are still prohibitively more expensive relative to fish oil, at least ten times. Unfortunately, complete replacement of fish oil with vegetable oil is still yet to be possible. The best practice for fatty acids requirement is to use two third vegetable oil and one third fish oil.
4) Traditional fishmeal can enable high phosphorous discharge at aquaculture due to non-optimised digestibility of phosphorous. This meant that fish needs to be fed with more total phosphorous to compensate for poorer phosphorous digestibility to meet its nutrition requirement. Undigested phosphorous discharge causes eutrophication. The issue is how can digestibility of phosphorous be increased so that less total phosphorous can be incorporated into sustainable fish feed with less phosphorous waste discharge.
5) Anti-nutritional factors in plants can interfere with food utilisation and affect the health, production, and even increase mortality of fish. Unlike ruminants, fish does not have the digestive system capable of coping with these anti-nutrients. High levels of dietary plant fibre can have negative impact on fish growth performance. The other most relevant and practical anti-nutrients that must be addressed include glucosinolates, saponins, tannins, soluble non-starch polysaccharides, gossypol, and phorbol esters.
Progress made in sustainable fish feed
Protein is the most important component in formulating sustainable fish feed alternative. The best practice is to have plant fibre below 8% by weight to avoid fibre’s anti-nutritional effect. It is often difficult to identify if the limiting factor of plant protein is really down to anti-nutrients or the lacking in certain amino acids such as taurine and methionine. This is because most studies observing the effects of anti-nutrients or nutrient deficiency were done in isolation but not together. This is ironic considering that using more protein substitute will naturally increase certain anti-nutrients while aggravating other types of nutrient deficiency. Some have observed that soybean meal can completely replace fishmeal as long as there is methionine supplementation to counter nutrient deficiency[vii].
Insect protein has also shown to be interesting alternative as it is lacking in anti-nutrients commonly found in plant protein. Insect is capable of recycling and converting agricultural waste (~1 billion tonnes annually[viii]) and food waste (~1.3 billion tonnes annually[ix]), whilst removing significant bulk of fibre and water. In Europe as of 1st of July 2017, has allowed processed animal protein from insects to be used for animals in aquaculture (EU-enactment 2017/893), of which Black Soldier Fly (BSF) is one of the seven insects approved. Black soldier fly (BSF) larvae have been shown to be capable of reducing pathogen counts in these wastes due to its immune-prophylactic[x] and having desirable taurine content[xi]. EU regulation, EC 1069/2009 (Chapter 2, Section 1, Article 11), stipulates that animal by-product may not be used to feed animals or farmed fish of the same species[xii], for fear of transmissible spongiform encephalopathies (TSE) although not such cases have ever been found in fish. Thus, waste from processed fish can also be fed to BSF larvae to introduce a trophic separation to prevent potential fish diseases being passed back to farmed fish while recycling omega-3 fatty acids back into the food chain. However, commercially available insect meal for commercial fish feed is USD$3000–3500 per tonne (by dry weight) which is USD1500–2000 per tonne more expensive than per tonne of fish meal. Co-blending of insect meal with plant protein would however be commercially competitive against fish meal as plant protein such as soybean meal, wheat gluten and corn can be obtained at USD$300–600 per tonne by dry weight. The cheapest implementation of BSF as fish feed would be to use palm oil product such as palm kernel cake as feedstock, thus allowing the price to drop to as low as USD2500 per tonne whereby more insect meal can be incorporated into sustainable fish feed.
As for phosphorous, there are a few methods to increase phosphorous digestibility to reduce total phosphorous in feed and effluent. The optimum ratio of calcium to phosphorous (Ca:P) especially if supplemented with vitamin D and/or citric acid[xiii], has to be less than 2:1 for increased digestibility of phosphorous and reduced total phosphorous content in feed. As a result, there is less phosphorous in effluent discharge.
Synbiotic is an important development whereby it combines both probiotics and prebiotics to increase the efficacy of probiotics for fish. Prebiotics such are as fructo-oligosaccharides, mannan-oligosaccharides, inulin and B-glucanare can stimulate and enhance the growth and activity of probiotic micro-organisms of fish. This will further reduce aquaculture’s dependency on antibiotics. Lactic acid bacteria or lactobacillus have been broadly used as probiotic strains. Lactobacillus can be cultured from fish silage that converts fish waste to alternative form of fish feed, whilst producing additional by-products that are beneficial for fish such as free amino acids and peptides. Utilisation of fish silage can replace 5–15% of the fish meal.
Moving forward
Aquaculture has come a long way into making fish feed sustainable. There is still a lot that needs to be done to improve the sustainability of fish feed. Future sustainable fish feed formulation will also need to have its key performance indicators measured against specific farmed marine species. Key performances to be measured against cultured marine species include specific growth rate, feed conversion ratio, and protein efficiency.
“This article was written in collaboration with Daniel Mahadzir as concept contributor and proofreader, and Ka-Kit Lee as a research analyst”
References:
[i] https://www.intechopen.com/books/microalgal-biotechnology/the-potential-for-next-generation-microalgae-based-feed-ingredients-for-salmonid-aquaculture-in-cont
[ii] https://www.weforum.org/agenda/2018/07/fish-stocks-are-used-up-fisheries-subsidies-must-stop/1
[iii] https://www.indexmundi.com/commodities/?commodity=fish-meal&months=240
[iv] http://www.fao.org/3/a-i5555e.pdf
[v] http://www.fao.org/3/AB412E/ab412e10.htm
[vi] https://doi.org/10.1016/j.aquaculture.2014.12.006
[vii] https://scialert.net/fulltext/?doi=jfas.2016.238.243
[viii] Agamuthu, P. Challenges and opportunities in Agrowaste management: An Asian perspective. Inaugural meeting of First Regional 3R Forum in Asia 11 -12 Nov., Tokyo, Japan. 2009.
[ix] http://www.fao.org/food-loss-and-food-waste/en/
[x] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5989015/
[xi] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5570497/
[xii] https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:300:0001:0033:EN:PDF
[xiii] http://depts.washington.edu/wracuw/front%20page/low%20phosphorus%20feeds%20final%203-5-13.pdf
