In Africa, the demand for tilapia is high but the supply of locally produced fish is insufficient. The market is comprised primarily of fish captured in the wild, or frozen fillets imported from China (FAO GLOBEFISH, 2013). Along with chicken, fish is one of the main sources supplying African requirements for Animal Source Foods (ASF), hence market prices need to stay affordable for all classes of the population. Intensive tilapia farming is expanding in sub-Saharan Africa along with growing and dynamic sectors in several countries. In Ghana in particular, large scale intensive commercial farms are developing to meet increasing local demand. In southern/eastern African countries like Zimbabwe, Zambia and Uganda, commercial tilapia production is now beginning to impact onto local and regional markets.
Intensive fish farms in Ghana rely on imported commercial feeds to enable economic production based on competitive Food Conversion Ratios (FCR’s). Small-scale farmers continue to use farm-made feeds from various waste and by-products. Access to locally produced, high quality feed ingredients is limited thus leading to importation of commercial feeds and feed ingredients, to ensure balanced diets and high performance (Hecht, 2007; Agbo, 2008). However, for many reasons such as the surge in prices of both fossil fuels and fishmeal prices, global commercial feed prices are constantly increasing (FAO GLOBEFISH, 2013).
The concentrations of fishmeal (FM) and fish oil (FO) in fish feeds are still considered to be the primary indicators of quality. FM is often the main source of proteins required and even if the concentration decreases every year (New and Wijkström, 2002; Olsen and Hasan, 2012), its use and demand continue to raise feed prices. Although tilapia is not the main consumer of FM when compared to other carnivorous cultured finfish and shrimp, the global production of tilapia is constantly increasing and intensive systems using commercial feeds are developing (Tacon et al., 2011). FM is generally the favorite source of protein in fish feeds due to its high quality nutritional profile and its high digestibility but the depletion of available natural wild caught fish has reduced a source of FM and there is a worldwide search to find a substitute, in order to limit its usage and reliance on it (NOAA/USDA, 2011; FAO, 2012).
Global research is seeking an alternate protein source that could provide fish feed requirements on a par with FM (Hasan et al., 2007; Ayoola, 2010). Continuous efforts are being made to find sustainable ingredients with nutritional value similar to FM, which can be produced at lower costs. Research has focused on several plant and animal by-products such as soybean and cottonseed meal, aquatic plants, legumes, blood meal, hydrolyzed feather meal, fisheries by-products, etc. (El-Sayed and Tacon, 1997; El-Sayed, 2004; Karalazos, 2007; Ayoola, 2010). Soya is widely used to supply protein requirements since it presents a comprehensive nutritional profile similar to FM, particularly for amino acids. However sustainability of production and transportation (GMO’s, deforestation, etc.) of soy is problematic due to competition for its use for human consumption, and in livestock feeds. There is widespread global interest in insect-derived proteins.
This can be seen in research, and commercial projects where researchers are examining the high potential for animal feeds and intend to develop scaled up sustainable insect rearing systems (van Huis et al., 2013). Invertebrates (crustaceans, worms and insects) constitute part of the natural feed for fish (Bailey and Harrison, 1948; Randall, 1967). They are also used in recreational fishing as bait. Since the 1980's insects have been used in aquaculture and for the reasons stated, promising results are anticipated.
In Ghana, there is a demand for local quality feed due to the rise of imported fish feed prices. Sustainable local production of insects is conceivable considering the environmental conditions. Fly larvae have been identified as a suitable and valuable source of protein for several livestock production systems, including fish (De Foliart, 2002; Odesanya et al., 2011; Van Huis et al., 2013).
Due to their high reproduction rate various species, such as Musca domestica or Hermetia illucens can be mass produced. Fly larvae (or maggots) production can be achieved at low cost from various sources of organic waste (manure, decaying fruit or vegetables, oil cakes, abattoir wastes, brewery solid wastes, etc.) and can be incorporated into fish feed as a principal source of animal protein. Larvae can be supplemented to fish feed as ?fresh? feed (alive, or frozen and chopped up) or can be processed by defatting, drying, and grinding, in order to convert them into maggot-meal (MM). In this analysis, which is a preliminary study, MM is considered. This model aims to assess where MM might best be used in the production chain, and to optimize its use and incorporation in tilapia diets during future insect-based feeding trials. Experiments will be implemented in 2014 and 2015 in both Ghana and the UK.
Results
All calculations in this study are based on substitution of 30% of FM content in tilapia diets, in each of the systems, (Sheppard et al., 2008). All results and intermediate calculations are shown in Table 2. Considering the total annual production of fry, fingerlings, food/grow-out fish, and the maintenance of broodstock, it appears that the total estimated amount of MM required to substitute FM in all diets is 237.7 MT (dry matter, DM). This figure represents 1886.9 MT fresh larvae (at 86 % moisture content) to be produced per year.
Annually, 1.4 MT (DM) of MM is necessary for the broodstock, 60.8 MT (DM) for the juveniles (fry and fingerlings), and 175.5 MT (DM), for the food/grow-out fish. 73.8% of the total amount of MM is required for the food/grow-out system only. In this system the quantity of feed distributed during the period necessary to reach a commercial size (longer than the time spent in hatchery/nursery), accounts for the estimated quantity of MM. The amount of MM required for the juveniles in this system represents 34.6% of the amount of MM required for the food/grow-out fish; younger fish have higher protein and fat requirements, particularly during sex-reversal and the fry to fingerling period, than sub-adults and adults (Fitzsimmons, 1997; Jauncey, 1998). Feeds must also be highly palatable at this stage to encourage feed intake, and attain a high rate of sex-reversal, hence a higher dietary inclusion of FM may be required. High quality and quantity nutrient requirements (protein and fat mainly) are required for broodfish, for reproductive efficiency (Santiago et al., 1985; Chang et al., 1988) but the amount of overall feed and MM required (to substitute FM) is relatively lower than for food/grow-out fish and juveniles, considering the number of fish maintained per annum.
This model will be used to design future maggot-based feeding trials on O. niloticus, to be implemented in partnership with an intensive cages-in-lake commercial farm in Ghana. Real production data will be used to estimate the quantity of MM necessary to substitute different levels of protein in formulated feeds for broodfish, juveniles, and grow-out fish.
Discussion
From this model the estimated annual amount of fresh larvae required to supply this farm is high (almost 2000 MT). Very few systems described in the literature are capable of producing this quantity of larvae. In theory, 3750 MT dried pre-pupae (Hermetia illucens Black Soldier Fly) could be produced annually in a 400,000 square foot facility in USA from 360 MT daily food leftovers or swine manure (Burtle et al., 2012). If this production level could be reached, this facility would be able to supply enough MM to manufacture fish feed with minimal FM inclusion. Fish farms larger than the one described in this model (which requires only 264.2 MT maggot meal annually) could supply maggot-based feeds. In China, the housefly larvae-bioreactor (Musca domestica) has also shown promising results with a total annual production of 760-960 MT fresh larvae (corresponding to 106-134 MT dried larvae, considering 86% moisture) from swine manure (Wang et al., 2013).
This is far from the requirements of the presented case. In Spain, housefly larvae (Musca domestica) production can supply up to 2.4-3.4 MT pupae per year by processing 500-700 kg fresh swine manure weekly (Pastor, 2011). Swine manure management is an important concern as this is a growing industry, and the accumulation of wastes will create major environmental and public health issues (contamination of surface water and groundwater) if not removed, treated, and/or reused (Aarnink and Verstegen, 2007). Crop fertilization and composting are the main solutions for manure management but the amounts generated (depending on the production system: feed, number of animals, etc.) exceed potential land use, and other handling is often costly. Fly larvae farming appears to be a sustainable management strategy, contributing to the reduction of manure volume and associated pollution risks, by converting the nutrients into a valuable biomass (Newton et al., 2005; Wang et al., 2013).
Central to MM production is consistent quality and quantity. The nutritional profile of fly larvae can fluctuate depending on the species, the phenological stage (larvae, prepupae or pupae), and the feeding substrate (Aniebo and Owen, 2010).
Consequently, strict traceability and consistency in the production process are needed. Studies show consistent dry matter content ranging between 91-95% for MM. However, crude protein (CP) content is more variable: 47.6% DM, and 63-64% DM, have been appraised for housefly pupae MMs produced from larvae fed on cattle blood mixed with wheat bran and chicken manure respectively (Calvert, 1979; Aniebo et al., 2009; Hwangbo et al., 2009), whereas BSF dried prepupae show a CP content ranging from 38-44% DM (Newton et al., 1977; Bondari and Sheppard, 1981; St-Hilaire et al., 2007).
When compared to FM, MM has lower but acceptable protein content, however amino-acid profiles are similar. MM amino-acid profiles are well balanced and this supports the use of MM, as opposed to other potential substitutes such as plants as a FM alternative without the need to supplement amino-acids. Theoretically this characteristic should enable good protein retention and growth of fish (St-Hilaire et al., 2007; Kroeckel et al., 2012). The fatty acid profile of fly larvae is easily manipulated as it is highly related to the larvae feeding substrate.
Feeding larvae with fish wastes could improve their lipid profile (which is similar to FM lipid profile) by complementing it with poly-unsaturated fatty acids (PUFA) ( St-Hilaire et al., 2007; Sealey et al., 2011). Thus MM would be preferable to other animal protein sources (Wang et al., 2013). Until problems of quality are better understood, and amino acid and fatty acid profiles optimized, replacing FM at a lower level is expected to be most effective. In the case presented here, nursery and grow-out operations are carried out in cages-in-a-lake where formulated feed is essential since natural productivity is low.
Consequently, considering its nutritional profile compared to FM and other potential FM substitutes, MM is a valuable substitute that could contribute to balanced formulated diets required for an intensive tilapia production system.
Depending on fish feeding response, growth, and breeding performance, a strategy for substitution of FM with MM can be formulated. Most fish species can be fed with maggot-based feed, but the effect will differ in different species. Secondary data on tilapia show diverse results. The most appropriate percentage of FM substitution for Oreochromis sp. appears to be dependent upon experimental conditions (duration of the trial, formulation of the diet, etc.) and on the maggot processing method (sun / oven drying, whole / chopped, defatted or not, etc.), which impacts on MM quality and digestibility.
In the Republic of Guinea, growth of O. niloticus increased when fed on a diet composed of 30% Black Soldier Fly Larvae (BSFL) meal and 70% rice bran, compared to growth when fed the traditional diet (100% rice bran) (Hem et al., 2008). After a 20 week trial, growth rate of O. aureus decreased when fed with whole BSFL only, compared to a commercial diet; fish growth performance improved when fed chopped larvae (Bondari and Sheppard, 1987).
Reduced digestibility was observed in O. niloticus fingerlings fed on a diet containing housefly larvae meal. This was related to the high ash content of the MM thus inclusion of only 15% was recommended to ensure acceptable growth (Ogunji et al., 2008). Comparable growth results of O. niloticus fingerlings fed respectively on a diet containing 56% housefly larvae meal (representing the exclusive animal protein source in the diet) and on a commercial feed (FM being the exclusive animal protein source) have been measured (Omoyinmi and Olaoye, 2012).
Fingerlings were used in previous maggot-based feeding trials to study growth performance and survival during the first months of the grow-out period. Although the amounts of MM necessary to substitute FM and to supply the nutritional requirements of the fish in a grow-out system are high (here 175.5 MT per year), studies have focused more on food/grow-out fish diets and performance. MM may be used in broodstock or juveniles diet supplementation. In these systems, the quantity of MM required would be minor, and production possible, given current production capacity and logistic challenges of supplying and managing substrates for maggot production. If for economic, logistic, or other reasons, maggots cannot be processed, supplementation of the broodfish diets using live or fresh chopped larvae (if the size of the mouth doesn’t allow ingestion of large particle size) can be envisaged.
In low-income countries, insect farming can be set up without major investment and high-tech equipment, and could rely on natural conditions and sustainable energy sources. A MM-based diet may be suitable for tilapia fry and fingerlings during the sex- reversal period and the ensuing months or weeks (before stocking in grow-out cages). The feed used is high in protein and other nutrients (lipids, vitamins, etc.), hence a high level of FM could be partially substituted with MM if fish performance does not suffer. Future trials will evaluate feeding response, survival, and performance of both broodstock and fry (egg production and viability) as well as success of sex-reversal and growth of juveniles. Results comparable to those observed with commercial feeds are expected.
In this model any real commercial or experimental data can be substituted to evaluate the amount of fly larvae and MM needed to substitute a certain level of FM in a formulated diet. According to the figures obtained, the amounts of MM required to substitute 30% of the FM inclusion in manufactured feeds used in a commercial intensive tilapia farm are far above the current production capacity of the facilities (fly larvae production systems) described in the literature. If fish performance is acceptable with maggot-based diets, improvement and development of efficient maggot production plants is expected to meet future demand. Meanwhile, the possibility of supplementation of broodfish or juvenile diets should be considered.
July 2014
