Introduction and methods
The rapid global expansion of Pacific white shrimp (Penaeus vannamei) aquaculture has intensified the demand for alternative protein sources to fishmeal. In this context, meals derived from Tenebrio molitor have already been successfully used as partial substitutes for fishmeal in diets for P. vannamei, with positive effects on growth, feed efficiency and immune response .Likewise, it is believed that the larvae of this insect can be fed with biofloc residues, establishing a sustainable strategy that converts biofloc waste into protein-rich biomass. In parallel, shrimp waste and fish by-products have also been tested as viable partial substitutes for fishmeal .Therefore, the aim of this study was to test biofloc-fed T.molitor and aquaculture by-products as fishmeal substitute and assess their impact on the shrimps' growth.
Three containers with T. molitor larvae were fed for one week, being provided with wheat bran and biofloc as a dry feed source at different inclusion levels (0%, 50%, 100%) until reaching an appropriate size for producing mealworm meal.Subsequently, five isolipidic, isoproteic, and isoenergetic diets were formulated using fishmeal (FM), T.molitor meal (T-50 and T-100), shrimp waste (Mix1), and Mugil cephalus by-products (Mix2) as the main sources of animal protein.
P.vannamei specimens with an initial average weight of 1.30 ± 0.0 g were distributed in triplicate for each experimental treatment and maintained in individual 1000 L tanks within an isolated biofloc technology (BFT) system, at a density of 200 shrimp/m2 for 88 days. At the end of the experiment, zootechnical parameters were calculated and 12 individuals from each treatment were sacrificed to evaluate their protein retention efficiency and intestinal microbiota through the amplification and sequencing of the 16S rRNA gene.
Results and discussion
Although the use of insects as a protein source for P. vannamei has been previously studied there is a lack of research focused on recycling biofloc waste as a substrate for T. molitor production. In this study, the inclusion of biofloc negatively affected larval performance, showing lower final weight, weight gain, and feed conversion ratio (FCR) and protein efficiency (PER) as biofloc inclusion level increased. However, this ingredient did not affect survival (Table 1). These results may indicate that either the insects didn't consume much of the provided biofloc or that an ineffective ingredient with poorly digestibility, yet safe for larvae, with greater potential at lower inclusion levels.
As for the shrimp trial, zootechnical results indicate that the protein source influenced the growth of P. vannamei. The Mix 2 and T100 diets showed the highest final weights and SGR, with significant differences compared to the control (FM). Moreover, survival was high in all treatments, with no significant differences between groups (Table 2).
Table 1. Growth performance and nutritional indexes of T.molitor fed with biofloc at different inclusi��n levels.
0%
50%
100%
Final weight (g)
0,12a ±0,001
0,10b ±0,001
0,08c ±0,001
Weight gain (g/larvae)
0,12a ±0,001
0,10b±0,001
0,08c±0,001
SGR (%)
1,92a ±0,498
2,85b ±0,063
3,98 c±0,159
PER (%)
2,54a ±0,016
3,99 b ±0,047
8,01c ±0,012
Survival (%)
99 ± 0,1
98 ± 0,1
100 ± 0,1
Note: SGR (Specific Growth Rate); PER (Protein Efficiency Ratio)
Table 2. Gowth performance and nutritional indexes obtained for P.vannamei fed with each experimental diet.
FM
T50
T100
Mix 1
Mix 2
Final weight (g)
9,16a ±0,270
9,57ab±0,745
11,99c±0,165
9,52ab±0,680
12,26d±0,290
FI (% day-1)
3,95 ±0,142
3,24 ±0,420
3,25 ±0,159
3,81 ±1,065
3,23 ±0,032
SGR
2,26a ±0,047
2,31ab±0,090
2,53abc±0,035
2,30ab±0,195
2,62 c ±0,082
FCR
2,34 ±0,070
1,89 ±0,240
1,81 ±0,066
2,28 ±0,700
1,78 ±0,012
Survival (%)
82,8 ±8,594
79,5 ±0,250
81,5 ±3,156
68,8±10,525
75,7±7,881
Nota: DFR (Feed intake); SGR (Specific Growth Rate); FCR (Feed Conversion Rate)
Therefore, these results support the feasibility of using aquaculture by-products and insect meal as total substitutes for fishmeal in shrimp diets. However, further research is needed to optimize alternative formulations in order to balance shrimp growth and feed efficiency, advancing toward more sustainable and circular aquaculture systems.
Acknowledgment
This work is part of the "ZeroFloc" R&D&I project PID2023-149570OB-I00, funded by MICIU/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR. Additionally, staff contracts have been funded by the ESF+ and by the European Union – NextGenerationEU, through the Plan of the Conselleria of Innovation, Universities, Science and Digital Society of the Generalitat Valenciana (INVEST/2022/434), and by MICIU/AEI/10.13039/501100011033 through the FPU program (FPU24/00525) and PRE2021-098367.
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