1. Introduction
The shrimp aquaculture industry has grown rapidly in recent decades and represents the most important aquaculture sector in Europe [
1,
2]. Consumer shrimp demand has increased in recent decades, leading fish nutrition experts to study the inclusion of vegetable by-products in aquatic animal feeding [
3,
4,
5].
Penaeus japonicus, kuruma shrimp, is one of the major shrimp species farmed in the seas [
6] that is used in the human diet since, like other shrimp species, it is highly appreciated from a gastronomic point of view as it is a good source of macronutrients (proteins and, particularly, essential amino acids) and vitamins and minerals (such as vitamin B12, iron, calcium and zinc) [
7]. Additionally, shrimps contain high levels of polyunsaturated fatty acids (PUFA), e.g., C20:5 n-3 (eicosapentaenoic, EPA) and C22:6 n-3 (docosahexaenoic, DHA) acids [
8], considered to be essential for human health [
9]. Japan was the first country to develop breeding system technology and it has since been transferred to China, Southeast Asia, India and Latin America. Over the last decade, various strategies have been employed to expand shrimp diets and address the global expansion of shrimp farming [
10].
In shrimp feed, the most nutritionally balanced and digestible ingredients are fishmeal and fish oil [
11]. However, their limited source and increasing prices encouraged fish nutritionists to test several alternatives in order to reduce fishmeal use [
5,
12,
13]. In the shrimp diet, depending on the species, from 25 to 50% fishmeal has been used; over time, both animal [
13,
14] and plant-based ingredients [
3,
15] have been investigated as alternative for fishmeal. Nevertheless, poor digestibility, an unbalanced nutritional profile, antinutritional factors, palatability and attractiveness remain challenging issues. During the juvenile stages, dietary protein content is the primary factor affecting shrimp growth [
16,
17]. Growth of aquatic animals occurs when, in the tissue, the quantity of protein synthesis exceeds the level of proteolysis [
18,
19]; therefore, the identification of sustainable alternatives having nutritional properties similar to fishmeal is ongoing. With regards to sustainability, international guidelines have been established by the European Union and the Food and Agriculture Organization of the United Nations (FAO) to manage by-catch and reduce discards from low-value marine fishes. The minimization of discards and their valorization in fish feeding as high-quality fishmeal or as a source of valuable protein, peptones, enzymatic mixtures, fish oil and bio-compounds are very interesting due to their environmental impact and to the economic feasibility of fish feeding [
20].
Seafood is defined as shellfish and fish found in estuarine, marine, freshwater and brackish ecosystems; the discards, including head, shell, guts, bones, skin, fins and other items, is the result of processing for the market [
21]. Furthermore, seafood discards are rich in long-chain PUFAs, essential amino acids, pigments, peptides, vitamins (B3, A, B12, B6, D) and minerals, along with a variety of nutraceuticals, including lipids, and polysaccharide-based compounds [
21]. Therefore, seafood discards may be considered as nutrients rich in bioactive compounds for shrimps. The addition of a low-cost fresh food, such as pilchard, anchovy, and mussel, to a dry feed may enhance either the growth or quality traits of post larvae, reducing feeding costs. According to the New Blue Economy Strategic Guidelines issued by the European Commission [
22], aquaculture has to produce food and feed with a lower climate and environmental impact than other types of farming.
This study was designed to assess the effect of the replacement of fishmeal with different levels (0, 25, 50 and 75%) of seafood discards in diets for Penaeus japonicus on growth performance, physical characteristics and the chemical and fatty acid composition of shrimp meat. The effects are estimated by cross-cutting PESTLE methodology with ESG indicators in order to provide the cost benefits and impactsz.
2. Materials and Methods
2.1. Animal Ethics
European animal welfare legislation does not regulate crustaceans [
23]. However, the animals were kept and slaughtered under production conditions; after being immersed in ice, they were subjected to analysis. They were not subjected to any procedures during the experimental period, and all analyses were conducted post mortem.
2.2. Experimental Diets
In this trial, juvenile shrimps with an initial weight of 0.5 g underwent a period of acclimatization (4 weeks) to the pond environment; afterwards, a total of 720 shrimps weighing 2.50 ± 0.50 g were assigned to the four isonitrogenous diets. The control diet contained 100% fishmeal, while the remaining three diets contained increasing levels of fishmeal replacement (25, 50 and 75%) by fresh seafood discards (SFs) based on a mixture of anchovy (
Engraulis encrasicolus), pilchard (
Sardina pilchardus) and mussel (
Mytilus galloprovincialis) in the ratio 1:1:2 (
Table 1). Discards were obtained by catching low-value fish and individuals of valuable commercial species below the minimum marketing size. The seafood discards were dehydrated at a low temperature (20 ± 5 °C) in a cool dryer to retain the chemical characteristics of the product, which were kept unaltered by removing water (Scubla Professional, Udine, Italy). In brief, in a vertical mixer, the feed ingredients, with additional vitamins and minerals, were thinly ground and mixed (M-750, Fanda, Zhengzhou, China); afterwards, fish oil was added and mixed. The diet clumped and formed a homogenous dough after slow addition of water. Then, the dough was extruded by a mill machine (SZLH-768 Shrimp Feed Pellet Making Machine, Richi machinery, Kaifeng, China) to obtain pellets with a diameter of 4 mm. For 24 h, the pellets were placed at room temperature to dry; then, they were broken and stored at −20 °C. Each diet was assayed in triplicate.
The trial lasted 108 days, and the shrimps were stocked in twelve cages (60 shrimps per cage, 3 m
3 for each cage) divided into the testing treatments and 3 repetitions. All the shrimp experimental groups were fed four times daily (at 6:00, 11:00, 17:00 and 22:00 h) from 10% (first week) to 5% (last week) of shrimp body weight [
24]. Weekly, the shrimps’ total weight for each cage was recorded in order to adapt the daily amount of feed administration.
The pelleted feeds and the dehydrated seafood discards were analysed by the AOAC method [
25] to evaluate the chemical analysis and fatty acid profile.
2.3. Growth Trial
The trial was performed in the commercial farm “Ittica Sardegna”, located in Santa Caterina, near San Giovanni Sergiu (CA) (Sardinia, Italy; 39.089479 N, 8.483647 E), using 3 m3 (1.5 × 2 × 1 m) cages placed on the bottom of a 1-hectare pond with a water depth of 1.0 ± 0.50 m. The cages were made of nylon with a 3–5 mm mesh diameter.
The water quality parameters were periodically measured, and the values recorded were optimal for the shrimps’ growth and survival (
Table 2). The temperature, salinity, pH and O
2 were monitored daily at 6:00 a.m. and 6:00 p.m., while total ammonia, nitrite, nitrate, and phosphate were controlled every two weeks (sensors of Softmakers S.R.L., Cittadella, PD, Italy). During the trial, a natural light–dark cycle was followed.
Pursuant to the laws in force [
26], after twelve weeks of the growth trial, the shrimps were caught by net and slaughtered by immersion in ice-cold water (hypothermia). Placed on ice, the shrimps were immediately transported to the laboratory.
Shrimps were individually weighed, after the standard length was measured and the growth parameters were subsequently calculated; the cephalothorax was separated from the abdomen manually, the exoskeleton was removed to obtain the abdomen weight without the exoskeleton, while the cephalothorax and the exoskeleton were weighed together using a precision balance (±0.01 g). The total exoskeleton length and abdomen width were measured with a digital calliper (0.1 cm precision scale).
The following indices were calculated [
27]:
- -
survival (%) = [final shrimp number/initial shrimp number] × 100;
- -
average weight gain (AWG, g/d) = (final body weight − initial body weight)/days of trial;
- -
weight gain (WG, %) = [(final body weight − initial body weight)/initial body weight] × 100;
- -
specific growth rate (SGR, g/%) = [(ln final weight − ln initial weight)/days of trial] × 100;
- -
meat yield (MY, %) = (weight of muscle/final weight) × 100;
- -
condition factor (K, g/cm3) = [final body weight/(body length)3].
2.4. pH, Colour and Warner–Bratzler Shear Parameters in Shrimp Flesh
The pH values were measured on the entire shrimp abdomen without exoskeleton using a portable instrument (Model HI 9025; Hanna Instruments, Woonsocket, RI, USA) with an electrode (FC 230C; Hanna Instruments) and performing a two-point calibration (pH 7.01 and 4.01).
Instrumental colour analysis was performed by HunterLab equipment (ColorFlex, Illuminant D65) in order to measure lightness (L*), redness (a*) and yellowness (b*) values. To make representative measurements, colour was assessed on three different parts (proximal, central and distal) of the abdomen of each shrimp. The whiteness index (w*) was calculated according to Chen et al. [
28]:
An INSTRON 5544 texture analyser (Instron US, Norwood, MA, USA) was used to determine flesh shear force (Warner–Bratzler Shear, WBS). The shrimp’s second abdominal segment was sheared in a perpendicular direction and the record of the maximum shear force was taken during cutting. All the analyses were performed in triplicate.
2.5. Chemical Composition and Fatty Acid Profile of Flesh Shrimp
Chemical composition of the shrimp flesh was analysed according to the AOAC procedures [
25] as described in our previous work [
29]. The total lipids were extracted [
30] and analysed by gas chromatography (Shimadzu GC-17A) as described in Tarricone et al. [
31].
2.6. Economic, Social and Governance Impact
PESTLE (Political, Economic, Social, Technological, Legal and Environment) analysis is a strategic planning tool to identify the external factors affecting a particular industry or sector [
32]. This analytical framework can provide valuable insights into the external factors that may impact the aquaculture sector’s growth and sustainability [
33,
34]. In particular, conducting a PESTLE analysis of the blue economy sector can help stakeholders to identify the opportunities and challenges that arise from these external factors [
33].
Environmental, social and governance (ESG) ratings provide guidance on a company or financial instrument’s sustainability profile or characteristics, exposure to sustainability risks or impact on society and/or the environment. ESG investing involves analysis of the extra-financial elements of company performance. In order to make sustainability information as relevant as financial information, the practice involves identifying the sustainability issues that are financially relevant, or material, to the business model of companies [
35]. These are commonly referred to in industry as key issues [
36]. Materiality is based on the theory that good ESG performance brings better financial performance, but only if companies focus on the key issues that are financially material to them [
37].
For this study, the indicators considered are ESG 1 energy efficiency, ESG 3 training and qualification, ESG 9 revenues from new products (shrimp with new sustainable diet), ESG 12 waste and discards, ESG 19 investment in accordance with ESG principles, ESG 20 supplies agreement and supply chain partners screened for accordance with ESG principles, ESG 21 health and safety aspects, ESG R&D expenses, ESG 28 customer retention and ESG 29 customer satisfaction. The indicators were calculated as follows using GRI 13 (Global Return investment) for fishery and aquaculture 2022, PESTLE parameters and the number of diets (4), as well as the different ratio of feed compositions (100%, 25%, 50% and 75%) with replaced fishmeal and the final eatable products.
where
x represents each ESG; 1, 2, 3, 4 represent the diets,
y = PESTLE and
n = number of years for scale-up.
In this study, the SGR parameters were analysed according to the three indicators by IT tools integrating artificial intelligence and managed by Aquacloud™, and the findings demonstrated the following:
- (a)
the integration of feed for shrimps based on discards from both the fishery industry and aquaculture is a key driver of application in the circular economy and on sustainability;
- (b)
the massive production and increasing demand for shrimps at the worldwide level can be managed by sustainable production based on a diet integrated with noble proteins from other blue resources otherwise destined for disposal and not recoverable, which are rich in functional compounds;
- (c)
sustainable supply chains are able to intercept with circular economy principles, according to the General Fisheries Commission for the Mediterranean (target 2 and target 3) [
38,
39];
- (d)
the proposed feeding system would have a positive impact in terms of ESG principles toward the SDGs (Sustainable Development Goals) because they affect cross-cutting elements between three sectors, aquaculture/fisheries, feeding and technologies, helping achieve SDGs 14, 2, 8, 10, 13, 15;
- (e)
the proposed feeding system has a positive impact in terms of upskilling and reskilling because it introduces the integration of competences toward new job placements and a more sustainable workforce.
2.7. Statistical Analysis
Statistical analyses were performed with SAS software 9.1 2004 [
40]. The Shapiro–Wilk test was conducted to verify the normal distribution of data, while the modified Levene’s test was employed to assess the homogeneity of variances. In order to evaluate the effect of the diet data, a one-way analysis of variance (ANOVA) was used; Duncan’s test was performed to compare differences among diets. Significance was declared at
p < 0.05. Data are presented as means and standard error of means (SEM).
4. Conclusions
In conclusion, feeding seafood discards provided satisfactory results with regard to performance and meat quality. Fishmeal replacement at 75% showed a higher value of hardness, a greater crude protein and lipid content, a lower saturated fatty acid concentration and, in turn, a greater amount of polyunsaturated fatty acids in shrimp meat. In addition, the shrimps fed with high levels of seafood discards (50 and 75%) showed lower atherogenic and thrombogenic indices.
Therefore, fishmeal replacement with seafood discards may represent a promising opportunity in juvenile shrimp feeding, in addition to its great advantages in terms of sustainability and the circular economy. Further investigation is needed in order to assess the effectiveness of this feeding regimen for the achievement of prawn commercial size. The opportunity for ESG compliance is shown by integrating the effects in the long term, up to 5 years, for the implementation of the methodology and its sustainable scale-up updated with the regulatory framework.