**4. Organic manure and fish growth**

*Innovation in the Food Sector Through the Valorization of Food and Agro-Food By-Products*

In the aquaculture sector, Africa produced about 1400 tonnes of fish from freshwater aquaculture in 2018, but most of this came from Egypt, which contributed more than 70 percent of the total production (**Figure 1**, Data obtained in [3]). Major aquaculture producers in 2018 with more than 10,000 tonnes include Egypt, Nigeria, Ghana, Uganda, Zambia, Kenya, Tanzania, and Zimbabwe. Production has increased three times for the past ten tears from 563,000 in 2008 to 1,440,000 in 2018 (**Figure 1**, [3]). In general, African aquaculture production is overwhelmingly dominated by finfishes (99.3%), with only a small fraction of production from marine shrimps and mollusks [23]. Among the freshwater cultured finfishes, tilapia farming is the main product, which is also the most popular fish from a consumer perspective. Aquaculture production in Africa is also increasing as presented in

In Africa, aquaculture systems are made up of extensive and semi-intensive systems. Small-scale earthen ponds (extensive systems) are characterized by low inputs and low yields. However, semi-intensive systems are characterized by human intervention where by fertilization is done to improve feed availability, hence, improved fish yield. In East Africa, semi intensive mainly used to produce *Oreochromis niloticus* and *Clarias gariepinus* in either monoculture or polyculture [24]. They consist mostly of earthen ponds, liner ponds and concrete ponds.

Other systems include cage particularly in areas with large water bodies including East Africa great lakes. Cage culture involves holding organisms under captivity within an enclosed space while maintaining free exchange of water. Cages use the existing water bodies, therefore, require comparatively low capital outlay and use simple technology, they can be used not only as a method for producing cheaply and high-quality protein but also for cleaning up eutrophicated waters through the culture and harvesting of caged planktivorous species. Although fish farming in cages in the existing water body is considered inexpensive relative to pond construction and its associated infrastructures [25], the feasibility and profitability of fish cage culture is influenced by the cost of input invested and revenue collected

Although not common, re-circulating aquaculture system (RAS) has been used in some countries particularly South Africa. RAS refers to a fish farming technology that reuse wastewater from tanks/rearing premises [26]. Water reuse in RAS is supported by both inline and end pipe treatment using a series of mechanical filter for solid waste removal, bio-filter for dissolved nitrogenous waste removal and sludge pond to settle suspended solid [27]. RAS technology is termed as sustainable advanced production system that provides constant and independent production conditions and reduces water consumption compared with semiintensive pond aquaculture, RAS technology provides high fish productivity with better effluent control of environmental conservation [28, 29]. Some of the sub Saharan countries have benefited from high temperature to which RAS performs efficiently [30]. The adoption of the system is low due to high cost of initial capital investment in tanks and high cost of electricity required in running the system and feeds. This has therefore called for sustainable aquaculture by integration of fish with livestock. Such integration involves the recycling of livestock wastes and processing by-products as manure and/or direct food for fish. Today, aquaculture in developing countries is mostly a small-scale activity and is usually not practiced as

**58**

**Table 1**.

from output.

**3. Aquaculture production systems**

The production volume and market share of aquaculture products are advancing extremely rapidly. However, feed is usually recognized as the single largest cost to producers, hence, the best way of reducing the cost of fish production is using organic manure and supplementary feed when available. Animal manure is widely used in developing countries in fish production in earthen ponds. The quality of manure as a fertilizer varies depending on the source of animal and the quality of feed fed to the animal [31, 32]. Research showed that pig, chicken and duck manures increase fish production more than cow and sheep manure. For example, in Asia, fish farming is probably the only branch of animal husbandry in which the use of manures is a traditional management tool. In Sub-Saharan Africa, ponds are fertilized using organic manures such as cow dung, sheep, poultry or rabbit manure [33]. The use of animal manure to fertilize ponds has been widely practiced in many countries in order to increase plankton so that there is more natural food for fish to eat, hence, high fish production. Manuring is therefore considered a cheap and preferred source of nutrient to increase fish production.

Pond fertilization with animal manure stimulates production of bacteria, phytoplankton, zooplankton, and benthic organisms [34]. The use of animal waste (livestock) has been studied under integration systems in Africa [35–37] and extensively in Asian countries [38, 39]. Benefits of integrated Agro-aquaculture systems have been reported in resource poor areas particularly in developing countries [38, 40, 41]. Studies conducted in sub-Saharan countries on the integrated aquaculture and agricultural systems are presented in **Table 2**.

Several studies showed that organic supplements contributed to fish yields by supplying P, N and C for algal growth and by stimulating detritus production and heterotrophic utilization. It is well known that high fish yields can be achieved through abundance of plankton in the cultural system [46]. Africa has vast resources of livestock and poultry, which play a vital role in pond fertilization. Livestock wastes including animal manure and poultry by-products are valuable resources in fish farming [47]. Livestock manure contains protein content of about 15 percent, energy (1250) kilocalories per kilogram, manure, and soluble vitamins [48].


#### **Table 2.**

*Studies on the integrated agro-aquaculture in sub-Saharan countries.*
