The global human population is on the rise, and projections have shown that by 2050, approximately 9.7 billion people will be inhabiting the globe (Béné et al., 2015; Shumo et al., 2019). This increase in population is directly impacting pressure on the global food basket. To meet the food demands of the increasing population, 70% more food needs to be produced globally (FAO, 2009; Schiavone et al., 2017; Shumo et al., 2019). Both capture fisheries and aquaculture sectors have been geared into providing fish and other aquatic products to the increasing population (Tidwell and Allan, 2001). However, the capture fisheries have been over exploited, leading to massive reduction in the fish yields. FAO (2018) and Barroso et al. (2014) reported a decline in the capture fisheries yields from 81.2 million tons in 2015 to 79.3 million tons in 2016. The main reason attributed to this decline was the El Niño effects.
With these declines, more focus is being put into aquaculture to increase the yields and hence bridge the gap. Currently, aquaculture is one of the fastest growing food sectors that is focused on providing quality, affordable and reliable protein sources to improve the livelihoods, curb malnutrition and reduce food insecurity (FAO, 2010; Béné et al., 2015). However, the industry’s growth is slow, and this has been put into close context with the industry’s high dependency on high quality protein feeds (Opiyo et al., 2018). Fish feeds contribute to over 60% of the total operational costs in a fish farm (Munguti et al., 2012) in which protein is the key nutrient needed in the feeds, and probably the most expensive one (El-Sayed, 1999; Munguti et al., 2012). Fish meal (FM) has been an important component in fish diets due to its high digestibility and acceptance alongside its high protein, essential amino acids and fatty acids profiles (Tacon and Metian, 2009). Recent studies have shown that fish meal stocks particularly in Kenya are declining due to over-exploitation alongside the seasonal closures of the Lake Victoria’s Omena (
The black soldier fly (
Proximate composition of the analysed ingredients used in diet formulation (as fed basis)
Tabelle 1. Rohnährstoff- und Energie-Gehalt der Futterkomponenten (Angaben auf Basis Lufttrockenmasse)
DM = Dry matter, NfE = Nitrogen Free Extracts, ME = Metabolizable energy.
DM | g/kg | 906 | 937 | 958 | 905 | 920 | 894 |
Crude protein | g/kg | 666 | 621 | 253 | 273 | 423 | 322 |
Crude fibre | g/kg | 80 | 59 | 80 | 287 | 179 | 95 |
Ether extracts | g/kg | 96 | 124 | 273 | 86 | 99 | 114 |
Ash | g/kg | 287 | 300 | 147 | 53 | 53 | 32 |
NfE | g/kg | - | - | 205 | 205 | 166 | 331 |
ME | MJ/kg | 13.6 | 13.8 | 16.2 | 10.2 | 12.4 | 13.8 |
Analysed Amino acid composition (g/kg feed; g/kg protein) of fish meal and black soldier fly larvae meal
Tabelle 2. Aminosäurezusammensetzung (g/kg Futter; g/kg Protein) von Fischmehl und Larvenmehl der Schwarzen Soldatenfliege
Histidine | 13.6 | 21.8 | 6.5 | 25.7 |
Threonine | 22.8 | 36.7 | 11.1 | 44.0 |
Arginine | 33.4 | 53.8 | 13.7 | 54.2 |
Valine | 28.8 | 46.4 | 16.3 | 64.4 |
Isoleucine | 25.4 | 40.8 | 12.0 | 47.5 |
Phenylanine | 23.8 | 38.3 | 11.7 | 46.2 |
Leucine | 44.1 | 71.1 | 19.1 | 75.6 |
Lysine | 42.6 | 68.6 | 16.7 | 66.2 |
Methionine | 16.3 | 26.2 | 4.5 | 17.6 |
Tryptophan | 5.5 | 8.8 | 3.4 | 13.5 |
Alanine | 41.5 | 66.8 | 18.7 | 73.9 |
Tyrosine | 18.8 | 30.2 | 18.0 | 71.3 |
Glycine | 37.6 | 60.5 | 13.9 | 55.1 |
Asparagine | 51.5 | 83 | 25.8 | 101.8 |
Glutamate | 92.6 | 149.1 | 34.5 | 136.2 |
Serine | 20.1 | 32.4 | 11.8 | 46.8 |
Cysteine | 3.5 | 5.6 | 2.5 | 9.8 |
Fish meal - Omena (
Black soldier fly larvae meal.
Calculated essential amino acid (EAA) content (g/kg feed) of the test diets used for feeding Nile tilapia in the experimental ponds for 72 days. aD1 = Diet 1, bD2 = Diet 2, cD3 = Diet 3, dD4 = Diet 4.
Tabelle 3. Errechneter Gehalt an essentiellen Aminosäuren in den Rationen (g/kg Lufttrockenmasse), die über 72 Tage an Tilapia verfüttert wurden. aD1 = Ration 1, bD2 = Ration 2, cD3 = Ration 3, dD4 = Ration 4.
Histidine | 9.4 | 8.6 | 8.4 | 6.9 |
Threonine | 16.5 | 15.4 | 14.9 | 13.2 |
Arginine | 30.8 | 29.0 | 28.4 | 25.2 |
Valine | 19.6 | 18.2 | 17.7 | 15.1 |
Isoleucine | 16.3 | 15.1 | 14.5 | 12.7 |
Phenylanine | 18.3 | 17.1 | 16.7 | 14.6 |
Leucine | 29.2 | 27.0 | 26.0 | 22.1 |
Lysine | 25.9 | 24.1 | 22.9 | 20.3 |
Methionine | 10.5 | 9.7 | 9.2 | 8.1 |
Tryptophan | 3.9 | 3.6 | 3.5 | 3.1 |
Four test diets were formulated by substituting FM protein with BSFLM at 0, 9.8, 19.5 and 29.3% of BSFLM, representing substitution rates of 0, 33, 67 and 100%, respectively. Starch was used as a filler material to top formulations to 100%. The formulation of the complete diet involved thoroughly mixing of the ingredients in the proportions given in Table 4. To attain a consistency for pelleting and make a soft dough of the powdered mixture, tap water was added. To obtain a homogenous diet, the feeds were minced several times, and pellets were made using a pelletizer. The pellets were sun-dried and stored at room temperature. The composition of test diets and their proximate nutrient content are shown in Table 4.
Composition and results from proximate analysis of test diets fed to Nile tilapia for 72 days containing different levels of black soldier fly larvae meal (BSFLM) as a replacement for fish meal (FM)
Tabelle 4. Zusammensetzung und Rohnährstoff-Gehalt von Rationen, die über 72 Tage an Tilapia verfüttert wurden und unterschiedliche Anteile an Larvenmehl der Schwarzen Soldatenfliege (BSFLM) als Ersatz für Fischmehl (FM) enthielten
Freshwater shrimp | 300 | 300 | 300 | 315 |
Fish meal | 220 | 148 | 74 | 0 |
Black soldier fly larvae meal | 0 | 98 | 195 | 293 |
Cotton seed cake | 200 | 200 | 210 | 200 |
Sunflower seed cake | 40 | 40 | 40 | 40 |
Maize germ | 177 | 154 | 167 | 73 |
Starch | 10 | 10 | 0 | 50 |
Fish oil | 52 | 49 | 13 | 28 |
Premix | 1 | 1 | 1 | 1 |
DM | 915 | 911 | 912 | 927 |
Crude protein | 309 | 313 | 303 | 303 |
Ether extracts | 140 | 116 | 115 | 153 |
Crude fiber | 98 | 98 | 81 | 164 |
Ash | 143 | 113 | 93 | 255 |
NfE | 225 | 271 | 320 | 52 |
ME (MJ/kg) | 11.5 | 12.2 | 12.2 | 11.0 |
DM = Dry matter, NfE = Nitrogen free Extracts, ME = Metabolizable energy.
D1 = Diet 1,
D2 = Diet 2,
D3 = Diet 3,
D4 = Diet 4.
Metabolizable energy (ME) calculated according to Pauzenga (1985): (ME = 37 × % CP + 81 × % EE + 35.5 × % NfE)/0.0041868
The feeding trial was conducted from October 2019 to January 2020 at Sagana fish farm (0°19'S and 37°12′E) of the Kenya Marine and Fisheries Research Institute (KMFRI). Male Nile tilapia fish were sourced from KMFRI Sagana Centre. The fish were acclimatized for 1 week in a hapa net (4 × 3 m) that was mounted on an earthen pond, during which they were fed with commercial floating feeds. Thereafter, 240 male
To evaluate the growth and feed efficiency, the following standard formulas were used:
Body weight gain (BWG, g) = final weight (g) - initial weight (g). Specific growth rate (SGR, %) = 100 × [(ln BW final (g) - ln BW initial (g)) / days of culture]. Feed conversion ratio (FCR) = feed provided/live weight gain (g). Protein efficiency ratio (PER) = live weight gain (g)/total protein intake (g). Survival rate (SR, %) = 100 × (final number of fish)/(initial number of fish).
The collected data was subjected to the Shapiro-Wilk test of normality followed by One-way ANOVA that tested differences in the growth response and survival rates of the stocked fish fed on different diets. To determine the pairwise differences among the diets, the Tukey-HSD post hoc test was employed. All the statistical analyses were performed using MS Excel and SPSS statistics (version 21). Results were interpreted to be significant at
The physico-chemical parameters analyzed are presented in Table 5. The physico-chemical parameters showed significant differences (p < 0.05) throughout the culture period.
Mean, minimum and maximum values of physico-chemical parameters of the water during the experimental period
Tabelle 5: Physikalisch-chemische Wasserparameter während des Versuchszeitraums (Mittelwert, Minima, Maxima)
DO = Dissolved oxygen, TDS = Total dissolved solids, PO4 = Phosphates, NO2 = Nitrites, NO3 = Nitrates, NH4 = Ammonium. Values represent mean ± SD, n = 3.
Temperature | °C | 25.8 ± 1.1 | 23.5 | 27.8 |
DO | mg/L | 6.8 ± 0.5 | 5.9 | 8.2 |
Conductivity | μS/cm | 71.6 ± 16.9 | 51.1 | 102.6 |
TDS | mg/L | 45.8 ± 9.8 | 33.8 | 63.1 |
Salinity | mg/L | 0.03 ± 0.01 | 0.02 | 0.05 |
pH | 7.4 | 9 | ||
PO4 | mg/L | 0.002 ± 0.0004 | 0.002 | 0.003 |
NO2 | mg/L | 0.001 ± 0.0002 | 0 | 0.001 |
NO3 | mg/L | 0.001 ± 0.0002 | 0.001 | 0.002 |
NH4 | mg/L | 0.01 ± 0.001 | 0.01 | 0.01 |
The two protein sources of interest, FM and BSFLM, had different nutritional composition (Table 1). BSFLM showed higher contents of EE, crude fiber, NfE, DM and ME in comparison to FM, whereas FM had higher contents of ash and crude protein than BSFLM. BSFLM contained lower concentrations (g/kg feed) of amino acids (Table 2) than those of FM. On the other hand, concentrations of essential amino acids (Table 2) in g/kg protein were higher in BSFLM than in fish meal with an exception for lysine and methionine.
Data on fish growth performance and survival rates are presented in Table 6. Mortality was very low and was only experienced in the early stages of the experiment.
Initial BW (g) | 51.6 ± 0.53 | 52.2 ± 0.60 | 53.0 ± 0.42 | 52.2 ± 0.74 | 0.445 |
Final BW (g) | 120.7 ± 6.98 | 124.5 ± 6.00 | 118.4 ± 7.16 | 112.8 ± 2.62 | 0.580 |
BWG (g) | 69.1 ± 7.33 | 72.3 ± 6.36 | 65.4 ± 7.45 | 60.5 ± 2.11 | 0.587 |
SR (%) | 96.7 ± 1.92 | 100.0 ± 0.00 | 100.0 ± 0.00 | 98.3 ± 1.67 | 0.248 |
SGR | 1.2 ± 0.09 | 1.2 ± 0.08 | 1.1 ± 0.09 | 1.1 ± 0.02 | 0.597 |
FCR | 1.0 ± 0.06 | 1.0 ± 0.06 | 1.0 ± 0.07 | 1.1 ± 0.01 | 0.647 |
PER | 3.3 ± 0.20 | 3.4 ± 0.18 | 3.3 ± 0.25 | 3.1 ± 0.03 | 0.826 |
BW - Body weight; BWG - Body weight gain; SGR - Specific growth rate, SR - Survival rate; FCR - Feed conversion ratio; PER - Protein efficiency ratio. Diets represent: Diet 1 - control (without black soldier fly larvae meal inclusion), Diet 2 (33% substitution rate), Diet 3 (67% substitution rate) and Diet 4 (100% substitution rate, i.e., maximum BSFLM inclusion).
No significant differences (p > 0.05) were found in the survival rates (SR). Further, the growth performance (BWG and SGR) and feed utilization efficiency (FCR and PER) were not compromised by the dietary treatments (
Growth trend curves displayed similarities and overlaps between the treatments from week 1 all through to week 7. Nevertheless, by the 9th week, there was a separation of the curves between the diets till the end of the experimental period. By the end of the experiment, the growth curves for diet 2 indicated the highest weight followed by diet 1 and D3, while D4 (100% BSFLM inclusion) resulted in the lowest, though not significant, weight.
FM and BSFLM (Table 1) used in the present study had a different nutritional composition. The BSFLM contained more EE, crude fiber (CF), NfE and metabolizable energy (ME) than FM, whereas FM showed a higher crude protein and ash content than BSFLM. FM had a negative value for NfE, and this may have been due to the fact that FM contains extremely low amounts of non-fibrous carbohydrates (Landau, 1992). The nutrient contents of FM used in the present study were similar to those reported by Cummins et al. (2017). The crude protein percentage of the BSFLM was similar to that obtained by Tschirner and Simon (2015), but lower than reported by Kroeckel et al. (2012) and Muin et al. (2017), who obtained levels exceeding 30%. On the other hand, EE of the BSFLM in the present study was similar to that reported by Devic et al. (2018) and Toriz-Roldan et al. (2019), but lower than that reported by St-Hilaire et al. (2017). BSFLM in the present study had lower contents of AA (g/kg feed) as compared to FM. However, when the amount of essential AA in the protein (g/kg crude protein) was computed, values for BSFLM were found to be higher than for FM with an exception of lysine and methionine. This is an indication that the nutritional value of the BSFLM (in terms of AA profile of the protein) may have been slightly higher than that of FM. A study done by Keembiyehetty and Gatlin (1992) showed improved survival and growth rates in fish fed on diets rich in dietary lysine. The calculated values of EAA (Table 3) were similar between the diets and met the suggested dietary AA contents for growth of Nile tilapia (Santiago and Lovell, 1988). Henry et al. (2015) argued that the variability in the nutrient contents of BSFLM can be attributed to factors such as type of substrate used to rear the larvae, stage of harvesting, methods of processing and duration of drying. Defatting of the larvae has been argued to lead to an increase in CP and reduction in EE (Castell, 1986; Renna et al., 2017; Dumas et al., 2018). Defatting of the larvae resulted in the increase of CP and AA and a decrease in EE contents as compared to the present full fat larvae (Kroeckel et al., 2012). Further, when 3 types of substrates were used to rear the larvae (Shumo et al., 2019), different nutritional contents were realized whereby the larvae that was reared on kitchen waste yielded higher EE contents in comparison to those reared on brewers’ waste and chicken manure. The 4 test diets (Table 4) met the nutritional requirements for tilapia commercial feeds (Munguti et al., 2014) except for diet 4 that exhibited unexplainably higher values of CF and ash than the recommended values.
All the fish appeared healthy and with no disease outbreaks throughout the 72-day trial period. All the measured water quality parameters (Table 5) were within optimal ranges for Nile tilapia growth and health (Popma and Masser, 1988). The mortalities were not diet-related but may have been due to the stress caused during fish handling at the time of stocking. Further, all the diets were well accepted by the fish, paralleling reports by Adewolu et al. (2010). There was no significant difference (p > 0.05) in the SR percentage in the present study between all the test diets (Table 6) which ranged from 96.7% to 100%. The present study mean SR was higher than that reported by other authors (Liu et al., 2012; Ye et al., 2012; Bulbul et al., 2013; Cummins et al., 2017) under clear water culture systems, but was similar to studies done by Ye et al. (2011) under green water culture systems, where the fish may have had continuous access to supplemental nutrients from the natural food web, hence increasing the chances of survival. Additionally, feed acceptance by the fish and good water quality parameters, that were well within the recommended ranges (Popma and Masser, 1988) may have further contributed to the high mean SR. No significant differences (p > 0.05) between the test diets were found for BWG and SGR (Table 6) in the present study. These results are in agreement with those of Toriz-Roldan et al. (2019) and Devic et al. (2018), when