Nutrition matters

Non-Conventional Feed Resources in Aquaculture: Potential Uses and Limitations

Tafadzwa Maredza, Lorraine K. Salimu & Milton T Makumbe

The world is being faced by an ever-expanding food demand which is likely to accelerate soon. There are number solid reasons to believe this futuristic bloom in global food demand. According to a report by the United Nations in 2019, the global population will grow to around 8.5 billion in 2030 and 9.7 billion in 2050 from an estimated 7.7 billion people worldwide in 2019. Of the additional 2.0 billion people who may be added to the global population between 2019 and 2050, 1.05 billion (52 per cent) could be added in countries of sub-Saharan Africa. Logically, a corresponding increase in food demand in this region is expected. Since the global human population is growing at a geometric rate vis-à-vis a slower arithmetic improvement in global food productivity, the human race is faced with an ever-growing need to take imperative measures to scale up agricultural productivity with the aim of meeting the ever-expanding global food demand, hence the growing adoption of practices such as aquaculture (fish farming) as a source of valuable fish protein to augment the dwindling fish supplies from the wild (capture fisheries).

In order to intensify fish production through aquaculture, adequate nutrition would be required for attaining high fish yields. However, feed accounts for up to 60% of total production costs in aquaculture. Therefore, it is every farmer’s wish to minimize feed costs as much as is sustainably permissible by utilising available feed resources. Let’s now have a discerning look at these feed resources useful in providing nutrition to fish.

Main Types of Fish Feed Resources

Fish feed can be delineated according to two main branches. Conventional and Non-conventional feed (NCFR). Conventional feed resources include a variety of feedstuffs regularly used in the formulation of fish feed. Their usage is standardized and widely acceptable. Examples include fish meal, bone meal, blood meal, soya bean meal, and maize and wheat mill products.

Contrary, NCFR refers to locally available feed stuffs that have not been traditionally used in animal feeding and/or not normally used in commercially produced rations for livestock. They are in most cases not consumed by man. In this sense, the NCFR could really be more appropriately termed “new feeds” and this term is in fact being increasingly used. Examples include feed stuffs such as kitchen waste, insect maggots, agro-industrial by-products like fruit peels and abattoir by-products, single cell proteins and water weeds.

Characteristics of NCFR

  • They are the end products of production and consumption that have not been used, recycled or salvaged.
  • They are mainly organic and can be in a solid, slurry or liquid form.
  • Their economic value is often less than the cost of their collection and transformation for use, and consequently, they are discharged for wastes.
  • The feed crops which generate valuable NCFR are excellent sources of fermentable carbohydrates, eg. Cassava and sweet potato.
  • Fruit wastes such as banana peels and pineapple pulp by comparison, have sugars which are energetically very beneficial.
  • Concerning the feeds of crop origin, the majority are bulky, poor quality cellulosic roughages with a high crude fibre and low nitrogen contents, suitable for feeding to ruminants and to fish at fairly very low inclusion levels or feeding rates.
  • Some of the feeds have deleterious effects on fish, and very little is known about the nature of the anti-nutritional factors and corresponding economically justifiable technologies of getting rid of these nutrition vices.

Problems Facing Fish Feed Industry and the Need for NCFR

Most conventional feedstuffs used in formulating fish rations are also consumed by man. These sources, as alluded earlier, include soya bean, ground nut, and our staple crop in Zimbabwe, maize. Since these feedstuffs are required almost exclusively for human consumption there is a great competition for food between human and livestock. With 77% of maize used as food and only 12% destined for livestock feed, there has been a great shortage of conventional feed resources such as maize and soya bean. Hence, conventional feedstuffs are dwindling in supply, and escalating in their cost. In contrast, NCFR are non-competitive in terms of human consumption suggesting their great potential as alternative fish feed sources. Also, the NCFR offer a cheaper and conveniently available alternative fish feed ingredient source. It is therefore necessitous to explore the potential benefits of utilizing non-conventional feedstuffs in aquaculture production in Zimbabwe.

Since fishmeal is expensive as a feed ingredient, the use of non-conventional feedstuffs has been reported with good growth and better cost benefit values. Fish meal has been traditionally used as the main protein source in fish feed industry due to its high protein content and a balanced essential amino acid profile needed to meet the protein requirement of most fish species. Fish meal is produced by processing products of fish such as mackerel, pilchard, capelin and menhaden into a dried and coarsely ground powder. The increased demand for fish meal, coupled with a significant shortage in global fish meal production, has created a sharp competition for its use by the livestock feed industry. As a result, fish meal has become the most expensive protein source in livestock and fish feed industries in the recent years. Hence the pressing need to attempt either partial or total replacement of fish meal with less expensive and locally available non-conventional protein sources such as black soldier fly (BSF) maggots, mealworm and abattoir by-products. In Zimbabwe, conditions are most favourable for the production and scaling-up of the aforementioned feedstuffs not traditionally used in formulating fish feeds.

Climate change is another global challenge facing aquaculture industry. Therefore, as a mitigation measure, locally evaluated and proven NCFR can be developed and multiplied to adapt against drought. Examples of these include pods of indigenous legume plants such as Sickel bush/Mupangara/Ugagu (Dichrostachys cinerea) and Monkey bread/Musekesa/ihabahaba, velvet bean (Mucuna pruriens), pigeon pea (Cajanus cajan), insect maggots, earthworm, snail, tadpoles and a variety of food processing by-products. Developing a multiple range of feedstuffs can potentially mitigate the risk of drought on fish farming in the region. Furthermore, NCFR can include resources otherwise regarded as wastes. Dumped food wastes normally ferment (decompose under anaerobic conditions) leading to an increase in greenhouse gas (GHG) emissions such as methane (CH4). Therefore, it is beneficially necessary to utilize food processing and consumption by-products as alternative feed sources of fish while providing a means of sustainably managing wastes, thereby reducing GHG emissions.

What is the Way Forward?

The Fisheries and Aquaculture Resources Production Department (FARD) is currently working on a baseline survey to unravel and inventory NCFR locally found in Zimbabwe. BSF larvae has been found to be the leading locally sourced and affordable NCFR where scientific research is being carried out to evaluate the potential and limitations of the feedstuff. Further training at farmer level through FARD is essential on the utilisation of on-farm feed formulations and the uptake of feed production.   FARD is therefore key in the prior scientific investigation on farm-feed suitability and offers these services to fish farmers in as a steppingstone to locally sourced, highly productive fish feed.

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