Insect meal is one of the best alternatives to partial or total replacement of fish meal, mainly because of its amino acid content and fatty acid profile quite interesting (Nogales-Mérida et al., 2018). The potential use of insect meal has recently attracted a lot of attention (Barroso et al., 2014; Henry et al., 2015). These insects are true sources of animal protein for fish, especially for continental species (Nyinawamwiza, 2007; Djissou et al., 2017). Increasingly, larvae of maggots (Musca domestica) are used as a partial or total replacement for fishmeal in the diet of tropical freshwater fish (Djissou et al., 2016). The high utilization of maggots in fish feed is due to their relatively easy production, relatively short production cycle (3-5 days) and above all their high nutrient content (Djissou et al., 2018). But their permanent availability and their nutritional quality conditions their use for obtaining good zootechnical performances.
For a large scale use of maggots in fish feed, many criteria including the production substrate, the production density by unit area and the production time are highlighted to make them available. The work of several authors has shown the different types of maggot production substrates. Most of these substrates are organic waste (Ajani et al., 2004; Djissou et al., 2015; Kovtunova et al., 2017; Pomalègni et al., 2016), food scraps or restaurant waste (Devic et al, 2018; Xiao et al, 2018). The ability of the flies to attract by the substrates (egg lying) is a function of the color, the texture and especially the odor released by them.
These characteristics as a function of ecological conditions determine the density of production of maggots that are harvested in different ways. Thus, our work has shown that when produced maggots are harvested by a sieve and hot water, the density of production by unit area is maximized. This is justified on the one hand, by the immobilization of maggots due to hot water (preventing them from sinking further into the substrate) since they are at this stage for most of the surface substrates (geotropism positive) and on the other hand, by the probable opening of the mesh of the sieve which allow more easily and quickly their harvest.
Results on the use of insects in the aquaculture of aquaculture species were carried out on the types of larvae used, their condition (fresh or dry, whole, defatted, etc.) or their heat treatment (sun drying, electric oven, lyophilizer) by Gasco et al. (2018). The results of our work revealed that the technological means of drying maggots harvested plays an important role in the physical and nutritional quality of dried maggots. These technological means, mainly depending on the temperature and the duration of drying, alter or not the physical quality of the dried product. This alteration or degradation of the product obtained is easily explained because the higher the drying temperature, the more the finished product is affected (degraded). Indeed, as the drying temperature increases, maggots undergo a biological alteration to their physical appearance (Djissou, 2017). This assertion is confirmed by the results of our work where freeze dryer drying (cold drying, 7°C) allowed the conservation of the physical appearance of the maggot (color, texture) unlike the electric oven (40°C) with a strongly degraded appearance. But these two means of drying require an energy cost unlike those using the sun as a source of energy with a slightly degraded aspect of the dried product at the level of the improved drying device.
Moreover, the biochemical composition of dried maggots varies greatly depending on the technological means used in particular for their protein and crude lipid contents. Freeze Dried Cypress and Enhanced Dryer have a high protein content compared to the others with the lowest content achieved with electric oven dried maggots. This indicates that the protein content of dried maggots decreases with increasing drying temperature. These results confirm the work of Djissou et al. (2017) who asserts that the chemical composition of biological samples are no longer conserved as the drying temperature increases thus denaturing the binding of peptide chains. The improved drying device maggots appears as the technological means of drying does not require energy cost of drying and to have a good nutritional quality of maggots.
Maggots that are sources of animal protein are high in protein with a good content of essential amino acids (Gasco et al., 2018). Its richness in vitamins including group A and its content in growth factor make it, besides the absence of cellulosic compounds and antinutritional factors, an excellent substitute for fishmeal in animal feed, especially fish. But the risk of bacterial contamination often arises for animal protein sources, hence the need to find an effective means of preservation in order to prolong its duration for effective use on the one hand, and to maintain its nutritional quality on the other hand share.
