Golden (Salmon from BrazilCharaciformes: Salmininae) is a large predatory fish native to South America (Flora et al., 2010), which has high commercial value. Due to the reduction of natural stocks and consequent limitation of commercial fishing, and due to its rapid growth, the dorado has attracted the attention of aquaculture companies (Rosa and Lima, 2008; Ribeiro and Portella, 2020). The feeding habits of the dorado, a strictly carnivorous fish, represent a great challenge for breeding and rearing, as the species requires expensive and high protein fishmeal (FM) feeds with sufficient amino acid profiles to achieve proper development and growth. (Fracalossi et al., 2004; Dairiki et al., 2013).
The growing demand for FM from the expanding aquaculture business, combined with the constant reduction of feedstock from fisheries bycatch (FAO, 2020), has led fish farmers to seek replacement of FM with less expensive and highly available (Hua et al., 2019). While FM remains an important ingredient in the larval and juvenile stages of cultured fish, lower levels are currently used in later stages of growth (Naylor et al., 2021). Despite their potential as a substitute for animal protein in aquatic feeds, plant proteins may be of limited use for carnivorous fish (Zhou et al., 2018) as they contain antinutritional factors and inadequate amino acid profiles (Pelletier et al., 2018) . To overcome the limitations of plant protein sources, extraction of non-protein components from plant-derived ingredients can result in concentrated products with high levels of protein (Xie and Jokumsen, 1997; Akharume et al., 2021). Soy protein concentrate (SPC), obtained by extracting carbohydrates and lipid fractions from soybean meal, is a promising source of vegetable protein to replace animal protein in aquatic feeds (Dersjant-Li, 2002; Gatlin et al., 2007). Although SPC is relatively low in essential amino acids (EAA), especially methionine and cysteine, it has low levels of antinutritional components (Storebakken et al., 2000; Dersjant-Li, 2002; NRC, 2011), is readily available in large quantities, and it has a low price compared to FM (Pezzato et al., 2002; Ray Gyan et al., 2019).
Several studies have been carried out on the use of SPC in the feeding of some species of aquaculture fish, including white sea bass,Centropomus viridis(Arriaga-Hernandez et al., 2021), Atlantic salmon (salmo salar) (Hartviksen et al., 2014), peito de ouroSparus aurata(Kissil et al., 2000), rainbow trout (Oncorhynchus mykiss) (Kaushik et al., 1995), to golden (Pagrus major) (Tola et al., 2019a) and yellow croakerLarimichthys crocea(Wang et al., 2017). Although fish tolerance to dietary SPC varies according to the species used as a model (Chen et al., 2019), 40 to 100% of the FM dietary protein can often be replaced by SPC without negative impact on fish growth performance. fish (Dersjant-Lee, 2002).
Replacing FM and fish oil with plant sources may affect fish health by altering their immune function and endocrine systems (Martin and Krol, 2017; Simo-Mirabet et al., 2018; Naylor et al., 2021), leading to to the development of disease and stress and subsequent reductions in feed intake and growth and production losses (Naylor et al., 2021). Improving voluntary feed intake is therefore a decisive step in optimizing fish growth and survival.
Food intake is regulated by hormones that either stimulate (orexigenic) or inhibit (anorexigenic) consumption in both mammals (Parker and Bloom, 2012) and fish (Volkoff, 2016). These appetite-regulating peptides are produced both in the brain and in peripheral tissues such as the gastrointestinal tract, and regulate food intake and digestive functions (Ronnestad et al., 2017; Soengas et al., 2018). Among the stimulants are orexin, and among the inhibitors cocaine and amphetamine-regulated transcript (CART), cholecystokinin (CCK), peptide YY (PYY) and leptin (Volkoff, 2016; Soengas et al., 2018;). Many of these hormones respond to the composition of diets and regulate energy homeostasis, ensuring optimal food intake, digestion and absorption of nutrients (Bertucci et al., 2019). Very little is known about how plant-based diets, especially SPC, affect feeding and appetite-regulating hormones in fish, as few species have been studied [p.Piaractus in Mesopotamia) (Volkoff et al., 2017); tambaqui (Colossoma macropomum) (Martins et al. Correa et al., 2020); Tilapia do Nilo (Oreochromis niloticus) (Ribeiro et al., 2016)].
This study aimed to evaluate the effects of graded levels (zero to 100%) of SPC replacing FM as a dietary protein source on feed intake and relative levels of transcribed gene expression of hormones that control feed intake. and digestion in golden chicks. The results of this study provide new insights into the development of plant-based protein diets that can maintain and enhance fish growth, health and well-being, promote the profitability and sustainability of aquaculture practices, as well as shed light on on the effects of dietary protein composition. in the regulation of appetite in carnivorous fish.
Materials and methods
Forsøg blev udført på Fish Nutrition Laboratory, Department of Animal Science, Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ), University of São Paulo (USP) and Piracicaba (SP, Brasilien; 22)°42′ 25” S, 47°38′ 29” W) (Fish Nutrition Laboratory, Department of Animal Science, Luiz de Queiroz College of Agriculture, University of São Paulo). The experimental procedures followed the guidelines of the ethical principles in animal experimentation of the Brazilian College of
Effects of dietary soy protein concentrate on feed intake
Daily feed intake was higher in groups fed 0% and 25% SPC compared to the other treatments. Fish fed 50% and 75% SPC had a daily intake of approx. 20% lower than for fish fed 0% and 25% SPC. Fish fed the 100% SPC diet had lower feed intake than all other groups (Fig. 1).
CCK expression levels in the foregut were higher in the groups fed 0%, 25% and 50% SPC compared to the fish fed 100% SPC. No differences were observed between fish fed 75% SPC and any of the other groups (Fig.
Several studies have investigated the effects of inclusion levels of SPC or other vegetable protein sources in fish feeds, but only a few studies [p. (Volkoff et al., 2017)] addressed the effects of 100% plant-based diets (restriction of crude protein content to an exclusively vegetable source of protein) on fish feeding and nutrition. This study evaluated feed intake and expression of appetite-regulating hormones in the intestine, pyloric cecum and hypothalamus of freshwater carnivorous fish fed diets
Declaration of competing interest
The authors declare no conflict of interest.
This work was supported by aSão Paulo Research Foundation (FAPESP)scholarship for R.E. Sabioni (grant #2015/23796-0) it is aNatural Sciences and Engineering Research Council (NSERC) Discovery Award(DG, grant number261414-03) for H. Volkoff. The authors would like to thank the company “CJ Selecta” for supplying the soy protein concentrate used in this research.
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