Aquaculture for all

Effects of Two Environmental Best Management Practices on Pond Water, Effluent Quality and Growth of Nile Tilapia

Nutrition Husbandry Education & academia

The trajectory of aquaculture growth in sub-Saharan Africa has necessitated closer attention to the use of environmental best management practices (BMPs). Two BMPs in particular, water reuse and floating feeds, are being promoted for adoption by pond fish farmers in sub-Saharan Africa.

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In this study, Emmanuel A. Frimpong et al, Virginia Polytechnic Institute and State University, investigated: (1) the effect of water source and feed type on water quality; (2) the effect of water source and feed type on tilapia growth; and (3) the quality of potential effluents from ponds using different water source and feed types

Aquaculture in sub-Saharan Africa is conducted mainly in earthen ponds and is relatively less intensive compared to the same method of food production in Asia, Europe, and North and South America. After many years of low production, efforts to expand the number of enterprises and increase the intensification of existing ones to increase productivity appear to be producing results.

The Food and Agriculture Organization (FAO) reported ‘rapid progress’ made by Nigeria, Uganda, Kenya, Zambia, and Ghana to become major aquaculture producers in sub-Saharan Africa. Ghana is one of the countries in sub-Saharan Africa with the potential to dramatically increase its fish production from ponds in the foreseeable future due, among other factors, to convergence of several auspicious events in the country.

These include: (1) progress in the development of a better performing strain of Nile tilapia Oreochromis niloticus, which is the major aquaculture species in the region; (2) the establishment of the first commercial fish feed mill in West Africa in the country; (3) the 2012 launching of the Ghana National Aquaculture Development Plan, developed in cooperation with the FAO, with an expressed objective of increasing Ghana farmed fish output from 10,200 tons in 2010 to 100,000 tons in 2016; and (4) a stabilizing political environment encouraging better governance of fisheries resources, as exemplified by a recent reinstatement of the Ministry of Fisheries and Aquaculture Development, independent of the Ministry of Food and Agriculture.

Intensification of farming is invariably accompanied by environmental problems, which can threaten the sustainability of the very growth that development experts agree is needed for food security. For example, almost all forms of aquaculture in the United States came under severe scrutiny and criticism in the 1990s for alleged poor environmental stewardship and the US, for example, responded with increased regulatory activity that led to a frenzy of research to respond to the new rules (e.g.).

Much research preceding and immediately following the imminent regulations focused on the characterization of effluents from various types of aquaculture under a range of management conditions and assessments of the impacts of aquaculture effluent on receiving waters. Consensus has emerged that pond aquaculture effluents are generally too dilute for conventional treatment options and that certain management practices, if applied properly, would help aquaculture achieve an equal or better environmental performance with less economic burden on producers. Today, best management practices (BMPs) are increasingly mainstreamed in larger aquaculture businesses, with internationally recognized bodies in place that certify farms voluntarily adopting responsible aquaculture practices, focusing comprehensively on the social, environmental and health dimensions. Guidelines and codes of conduct for responsible aquaculture with national and international foci also abound (e.g.).

Due to its history of being mostly small-scale, pond aquaculture in sub-Saharan Africa has not experienced a lot of scrutiny, but increasing scrutiny is predictable under the current rate of growth. Cage aquaculture in Africa has seen tremendous growth recently and is more conspicuous to environmentalists resulting in its being regulated in countries such as Uganda, Botswana, Mozambique, and Ghana (e.g.). Research, especially research directed at improving environmental performance of aquaculture in Africa, is not a current focus of national governments partly because there is a sense of crisis and the perception of needing to increase production at all cost. But when aquaculture development in the region comes under increased pressure for environmental stewardship, scientific data will be required to demonstrate stewardship or areas where improvements can be made. There is a wide variety of aquaculture production systems and management practices, but in the absence of data related to specific aquaculture types and management practices, there is the tendency to lump all aquaculture together and attribute common environmental problems.

The United States Agency for International Development (USAID)–funded Aquaculture and Fisheries (AquaFish) Innovation Lab (formerly AquaFish CRSP) has supported investigations over the past six years to identify the characteristics of pond aquaculture effluents and effluent receiving water bodies in Ghana and assess the impacts, if any, of aquaculture on these receiving water bodies. The results of the studies showed the presence of elevated total phosphorus (TP), total nitrogen (TN), total suspended solids (TSS), and biochemical oxygen demand (BOD5) in ponds relative to upstream sections of receiving streams and reference streams. In addition, water downstream of aquaculture facilities trended toward similar levels of the nutrients (TP and TN), TSS, and BOD5 as in the ponds. It was concluded that while the overall impact of pond aquaculture on receiving waters in Ghana was currently low, BMPs relating to nutrient and effluent management need to be widely adopted by fish farmers in the near future, especially as the number of fish farms and intensification of existing farms continue to increase. Subsequently, AquaFish has sought to develop and extend environmental BMPs widely to pond-based fish farmers in Ghana, Kenya, and Tanzania. One goal of the effort has been to pre-empt harsh regulations while keeping small-scale pond aquaculture profitable and environmentally benign.

The adoption of BMPs in fish production requires strategies that integrate profitability and efficiency in the fish farming enterprise. Nutrient and effluent management practices affect the volume of water, nutrients, solids, and oxygen demand loading rates from ponds into receiving water bodies.

Changing nutrient and effluent management practices has economic implications, beyond the potential environmental benefits. One way to assess environmental impact of changing practices is to empirically determine the net gain or loss in nutrients, solids, and oxygen demand in the pond water through the production cycle and the amount of water exiting the pond after production under the alternate management practices. This approach has been used to varying extents by various studies cited herein. Where there is negligible overflow or seepage from ponds, this analysis is relatively intuitive. The economic impact of changing practices on producers is assessed by determining the cost and change in production and profit associated with alternate practices (e.g.).

The focus of the current study was to quantify the quality of pond water and potential effluent under selected management practices and to determine the effect of these management practices on growth of Nile tilapia, Oreochromis niloticus. Detailed analysis of the economic impact of these BMPs on profitability for the producer and society is the focus of another study. The two BMPs selected for assessment are: (1) water reuse (as contrasted with draining ponds and refilling with new water at the end of each production cycle) and (2) the use of commercial-grade extruded or floating fish feed (as contrasted with sinking feed of the quality made on most farms), the former accomplishing both reduction of effluent volume and nutrient, solids, and oxygen demand whereas the latter primarily serves to reduce nutrient loads.

These two BMPs have clear alternative practices that are widely agreed to be the status quo, the BMPs are hypothesized to have significant effects on fish growth and pollution potential of ponds, and lend themselves to straightforward experimental manipulation so their environmental effects and economic benefits can be quantified accurately. Specifically, we investigated: (1) the effect of water source and feed type on water quality; (2) the effect of water source and feed type on tilapia growth; and (3) potential effluents from ponds using different water source and feed types.

Further Reading

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June 2014