Apparent digestibility for Zophobas morio meal in diets for juvenile yellowtail lambari, Astyanax bimaculatus (Linnaeus 1758)Abstract
Aquaculture is essential for food security and the yellowtail lambari is of great importance in Brazilian fish farming. Zophobas morio meal has emerged as a sustainable protein alternative for fish diets. This study evaluated the apparent digestibility of larval, pupal and adult meal of Z. morio in diets for lambari. The experiment, conducted at IFES and UFES, used 840 juvenile lambari. The animals were fed three times a day and feces were collected by the direct method eight times a days over a period of 22 days. The apparent digestibility coefficients (ADCs) for larva and pupa meal were significantly higher than the ADC for adult meal, due to their lower chitin content. Protein digestibility was highest for pupa meal, followed by by larva and by adult meal. Lipids of larva meal were more digestible than those of adult meal. There was greater gross energy utilization for larva and pupa meal than for adult meal. In conclusion, Z. morio meal is a promising feed for yellowtail lambari, especially that of the larval and pupal stages, due to its good digestibility and high nutritional value; adult meal has lower digestibility and requires additional treatments for improvement.
Key words
Aquiculture; Insect; Nutrition; Sustainability
INTRODUCTION
Aquaculture is one of the fastest-growing sectors of food production and plays a central role in global food security. According to the Food and Agriculture Organization of the United Nations (FAO 2024), global fish production reached 130.9 million metric tons in 2022, with aquaculture contributing 51% of this total, thus surpassing fishing for the first time. Latin America has seen a 10% growth in aquaculture production over the last decade, with Brazil standing out as the regional leader, being responsible for 14.9% of the region’s total production (FAO 2024).
The yellowtail lambari, Astyanax bimaculatus Linnaeus (1758), prominent among species of interest to Brazilian fish farming, as it is valued for both human consumption and as live bait. Characteristics such as rapid growth and high adaptability make the species ideal for small and medium-sized producers (Boscolo et al. 2002, Bicudo et al. 2010).
Although lambari farming has gained momentum in recent years, one of the main challenges faced by producers is the formulation of appropriate diets that can meet the nutritional requirements of the species in an efficient and sustainable manner. Studies indicate that, like other fish species, lambari have a high protein requirement, especially during the initial phases of development, which reinforces the need for high-quality ingredients to optimize fish growth and health (Furuya et al. 2013, Oliveira et al. 2008).
Historically, fishmeal has been the main protein source used in fish feeds due to its balanced amino acid profile and high digestibility (NRC 2011, Loureiro et al. 2024). However, dependence on this ingredient brings economic and environmental challenges, such as increased production costs and overfishing of marine species (Tacon & Metian 2008). To address these challenges, research into alternative protein sources, such as insect meal, has gained prominence.
Insect production for animal feed is internationally recognized as a sustainable strategy to meet the growing demand for protein (Van Huis et al. 2013). FAO (2013) highlighted the potential of insects, pointing out benefits such as reduced natural resource use and environmental impacts compared to conventional protein sources. In the European Union, Regulation (EU) No. 2017/893 authorized the use of insect protein in aquaculture feed, consolidating the legal basis for its expansion in the sector (Pisanello & Caruso 2018). These initiatives reflect the global relevance of insects to contributing to more efficient and sustainable production systems.
Studies have demonstrated the potential of insects to replace traditional ingredients in fish feed, with satisfactory results for digestibility and productive performance (Henry et al. 2015, Sánchez-Muros et al. 2016). In this context, Zophobas morio Linnaeus (1758) meal has emerged as a promising alternative. In addition to presenting a high amount of crude protein and a good essential amino acid profile, its production requires less use of natural resources, thereby contributing to production chain sustainability (Van Huis 2013). Thus, Z. morio meal presents promising characteristics, such as high crude protein content (47 – 63%) and good digestibility (Henry et al. 2015, Finke 2002).
Although research has shown positive results with the inclusion of insect meal in diets for fish such as tilapia and trout (Belforti et al. 2016, Piccolo et al. 2017), the use of Z. morio meal in diets for yellowtail lambari is still little explored, highlighting the need for research to evaluate its digestibility and zootechnical impacts. Digestibility, defined as an animal’s ability to take advantage of the nutrients in a food, is one of the main criteria for evaluating the viability of new ingredients in aquaculture (Ogunji et al. 2009).
Given the potential of Z. morio as a protein ingredient, and the relevance of lambari in Brazilian aquaculture, this study aimed to evaluate the apparent digestibility of the meal of larvae, pupae and adults of Z. morio in diets for juvenile yellowtail lambari (Astyanax bimaculatus).
MATERIALS AND METHODS
Location and animal ethics
The study was carried out at the Laboratório de Nutrição e Produção de Espécies Ornamentais (LNPEO) of the Instituto Federal do Espírito Santo (IFES), Alegre Campus, and the Laboratório de Bromatologia Animal (DZ/ UFES) of the Universidade Federal do Espírito Santo (UFES), Alegre Campus. It was conducted in accordance with the precepts of Law No. 11.794, of 8 October 2008, with the standards defined by the Conselho Nacional de Controle de Experimentação Animal (CONCEA) and approved by the Comissão de Ética no Uso de Animais (CEUA) of the Instituto Federal de Educação, Ciência e Tecnologia do Espírito Santo, registered under No. 23149.003781/2023-18.
Experimental diet preparation and feeding
Zophobas morio (ZM) meal was prepared using insects grown in dark-colored containers that were shaded with cloth to allow access to oxygen. Feed for the initial phase of swine was used in the diet with chayote as a source of moisture. Different containers were used for each phase of the reproductive cycle of the insects (larva, pupa and adult) for better control and development. The insects were killed by freezing (12 hours in a freezer), dehydrated in an oven for 24 hours at 65°C, and then milled with a knife mill (model TE 150/1), thus obtaining the meal.
The following four test diets were used: 30% ZM larva meal and 70% of reference diet; 30% ZM pupa meal and 70% reference diet; 30% ZM adult meal and 70% reference diet; and 100% reference diet as control. The diets were formulated in the Super Crac 6.1 program, so as to be isoproteic and isoenergetic, with 36% crude protein (CP) and 3.6 Mcal/kg of digestible energy (DE). The ingredients were prepared by grinding in a knife mill (Model TE 150/1) followed by sieving through a 0.5 mm mesh. They were then homogenized and subjected to pelletization in a C.A.F. electric meat grinder with an 8 mm disc. After pelleting all four diets, they were air-dried and subsequently ground in a manual mill using 0.5 mm sieves.
Fish and experimental conditions
The experiment used a total of 840 juvenile yellowtail lambari with an average weight of 2 ± 1.83 (g) that were derived from reproduction in the aquaculture sector. The fish were acclimatized in incubators for 15 minutes. The experiment was conducted using a completely randomized design, with four treatments and three replicates for a total of 12 experimental units. Each experimental unit consisted of a conical fiberglass incubator (modified Guelph) from Trevisan, with 80 liters of useful volume. The incubators were randomly distributed in a controlled space to ensure the independence of treatments. Each incubator contained 70 animals and was provided constant aeration by means of porous stones and temperature control by a 300 W thermostat.
The fish were fed until apparent satiety three times a day, at 7:00 a.m., 10:00 a.m., and 1:00 p.m. Feces were collected using the direct method over a period of 22 days, with total collection at 1:00 p.m. (before feeding), 3:00 p.m., 5:00 p.m., 7:00 p.m., 9:00 p.m., 12:00 am, 3:00 a.m., and 6:00 a.m. This was done using collectors regulated by registers attached to the bottom of the incubators. Feces were stored in plastic containers in a Consul Slim vertical freezer for later analysis.
Physicochemical analyses were performed at the Laboratório de Bromatologia Animal of the Departamento de Zootecnia at the Universidade Federal do Espírito Santo (UFES), Alegre Campus, according to the methodology described by the Association of Official Analytical Chemists (AOAC 2006). The following analyses were performed: moisture by direct drying in an oven at 105°C, mineral matter as residue by incineration in a muffle furnace at 550°C, proteins by the classic Kjeldahl method, and ether extract by ANKOM XT15 semi-automatic device. Gross energy analysis was performed according to Takeshita & Dias-Júnior (2017) using an Ika C200 calorimetric bomb at the Laboratório de Bioenergia of the Universidade Federal do Espírito Santo, Alegre Campus. Digestibility coefficients were subsequently calculated for each of the parameters analyzed using equations following the methodology described by Rostagno et al. (2007).
Water quality parameters
Partial water changes of 40% were performed three times a week to maintain water quality parameters appropriate for the studied species and to avoid influencing the experimental results. Water physicochemical parameters were monitored every two days throughout the experimental period. Temperature, pH and dissolved oxygen measured with a YSI 6920 V2® multiparameter probe (Yellow Springs Incorporated - YS, Yellow Springs, OH, USA) and were 27.5 ± 0.80 °C, 7.2 ± 0.90, and 5.8 ± 1.50
mg.L-1, respectively. Total ammonia was determined based on descriptive methodology using standard methods for the examination of water and wastewater (Eaton & Franson 2005) and was 0.15 mg.L-1 ± 0.012.
Statistics
The resulting data were submitted to ANOVA followed Tukey’s test (5% significance) for comparison of means, using the open access computer program Genes.
RESULTS
The apparent digestibility coefficients (ADCs) for larva, pupa and adult meals of Zophobas morio are shown in Table I. For yellowtail lambari, it is important to emphasize the relevance of considering the chemical composition of Z. morio throughout development as well as the metabolic changes that occur.
Apparent digestibility coefficients for nutrients of Zophobas morio larva, pupa and adult meal for yellowtail lambari.
DISCUSSION
Observed ADC values for dry matter were significantly higher for Zophobas morio larva (97.77%) and pupa (97.42%) meal than for adult meal (43.11%; Table I). This high digestibility for the larval and pupal phases can be attributed to the presence of less structural components such as chitin, which occur in greater quantities in the adult phase.
According to Henry et al. (2015), chitin, a structural polysaccharide present in the exoskeleton of insects, is difficult for fish to digest because most species lack chitinase enzymes. Furthermore, the lower structural complexity of larvae and pupae favors nutrient absorption, which is reflected in high ADC values (Sánchez-Muros et al. 2014).
Observed ADC values for crude protein were highest for Z. morio pupa meal (57.05%), followed by larva meal (54.84%) and then adult meal (42.30%). This variation is directly related to metabolic and structural changes throughout the life cycle of Z. morio. During the adult phase, proteins associate with structural components of the exoskeleton, making them less accessible for digestion (Lock et al. 2016). On the other hand, pupae have more easily degradable proteins, as they are in a transition phase that demands great mobilization of metabolic resources (Barroso et al. 2014).
The reduced digestibility of adult Z. morio can be explained by the association of proteins with chitinous structures and other complex molecules (Henry et al. 2015). This trend is consistent with the literature, where larvae and pupae are often described as ideal phases for obtaining meal with high protein digestibility (Barroso et al. 2017). Observed ADC values for ether extract revealed a decreasing trend from Z. morio larva (25.23%) to adult (22.49%) meal, with intermediate values for pupa meal (21.83%; Table I). This reduction can be attributed to the varying lipid composition among development phases.
According to Ojha et al. (2021), larval lipids are generally richer in unsaturated fatty acids, which are more digestible, while adults have more complex forms of lipids, such as lipoproteins and sterols, which are less metabolizable by fish. Additionally, the presence of lipids with low digestibility can negatively impact the total energy efficiency of a diet for fish (Rumpold & Schlüter 2013)
The observed ADC values for mineral matter showed less variability among Z. morio phases, with similar values for larva (3.93%), pupa (4.10%) and adult (4.03%) meal. However, the slight superiority for pupa meal can be explained by the greater retention of minerals during this phase of intense metabolic activity (Rumpold & Schlüter 2013).
The observed ADC values for gross energy were high for Z. morio larva (88.58%) and pupa (87.54%) meal, but significantly lower for adult meal (72.76%). This difference can be explained by the lower use of energy components, such as lipids and structural carbohydrates, in the adult phase due to the higher proportion of chitin and other difficult-to-digest substances (Henry et al. 2015).
It is evident that the developmental phase of Z. morio used in meal significantly influences its nutritional composition and the utilization of nutrients by fish. Barragán-Fonseca et al. (2017) suggest that larvae and pupae are the most promising phases for use in animal diets due to their favorable composition and high digestibility. On the other hand, adults, despite having lower digestibility, can be processed through techniques such as fermentation, enzymatic hydrolysis or partial removal of chitin to improve their utilization (Barroso et al. 2017, Rumpold & Schlüter 2013).
In conclusion, Zophobas morio meal presents promising nutritional characteristics for feeding yellowtail lambari, especially when using larval and pupal phases, which demonstrated greater digestibility and better nutritional utilization. These phases have high crude protein content, high gross energy and favorable lipid composition, making them viable and sustainable alternatives to traditional ingredients. On the other hand, the lower digestibility observed for the adult phase highlights the need for additional treatments to improve its use in feed.
Acknowledgements
This work was financially supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brazil, and the Instituto Federal do Espírito Santo (IFES).
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