Beneficial roles of Song-Gang stone as a feed additive in aquaculture: a review

Naturally occurring minerals are homogeneous material formed from one or a compound of elements through geological processes. Natural minerals are generally soil-based particles altered by the weathering action of bio-stone containing silicon dioxide (SiO₂) at 40%–80% and aluminum oxide (Al₂O₃) at 10%–30% as the main components (Yoon & Park, 2009). They can be used with other mineral oxides as effective and useful feed additives such as iron oxide (Fe₂O₃), calcium oxide (CaO), magnesium oxide (MgO), potassium oxide (K₂O), sodium oxide (Na₂O) and titanium oxide (TiO₂) in the diets for animal (Yoon & Park, 2009). Some studies have suggested a possible improvement of growth, immune response and water quality by supplementing natural minerals in fish diets (Table 1). Naturally occurring minerals may also fight gastrointestinal diseases by mixing with noxious compounds, altering nutrient usage in the intestine, and positively impacting animal health (Lv et al., 2015; Zhang et al., 2013). Natural mineral feed additives have some potential as replacements for antibiotics (Safaeikatouli et al., 2011; Yenice et al., 2015). In livestock, minerals delay the transit time of feed in the intestine. This mechanism of action improves acid capacity and feed use rate (Kermanshahi et al., 2011), increasing the absorption of moisture and the ability to trade in ions, thereby reducing the incidence of intestinal stools and harmful gasses which improve the environment (Joo et al., 2007). Feed quality improvements include inhibition of the survival of fungi and harmful bacteria and adsorbing toxins in the feed, thus improving the health of cultured livestock (El-Melegy et al., 2015). SGS is a naturally sourced and purified mineral material from the Republic of Korea comprising predominantly of iron oxide (Fe₂O₃), silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), potassium oxide (K₂O), sodium oxide (Na₂O), titanium dioxide (TiO₂), etc. (Lee et al., 2015; Won et al., 2017). It is considered to be one of the important naturally sourced mineral materials that improves the health status of fish (Choi et al., 2004; Lee et al., 2015; Won et al., 2017). For the confirmation of ingredients of mineral mixture, the X-ray fluorescence spectrometer (XRF) (ARL PERFORM’X, Thermo Fisher Scientific, Waltham, MA, USA) was used to determine the mineral composition of the mixture (SiO₂, Al₂O₃, Fe₂O₃, CaO, MgO, K₂O, Na₂O, TiO₂) according to the method (KSE3076) of Korean standards for mine (Korea Standard Association, 2002). In brief, a certain amount of each of the pulverized sample and a binder (polyvinyl chloride or PVC dissolved in toluene) was added carefully, mixed and pressed in a hydraulic chamber to form a pellet. The sample chamber (analyzer) of the spectrometers was then fitted with the pellet and the X-rays emitted at a voltage (up to 30 kV), and with a current (up to 1 mA). The software attached to the spectrometer was then calibrated and operated for around 30 to 60 seconds, and the results were then displayed automatically (Table 2). These natural minerals are like zeolites, which are commonly used in aquaculture as an additive. Zeolite mainly has a SiO₂ component and other components of the primary mineral source, some of which are micronutrients (Roland & Kleinschmit, 1996).

The previous studies of SGS in fish are summarized in Table 3. The effectiveness of SGS has been evaluated as a dietary supplement for a variety of cultured aquatic organisms. Evaluations of this sort generally consider time-course, dosage, and the responses of fishes or crustaceans to experimental exposure as seen in their growth performances, immune status and disease resistance. The SGS is a rich mineral source, which reduces the entry of pathogenic bacteria through the adsorption of harmful gas. It is free of toxins and heavy metals, and is recognized as having some potential as a healthy, low-cost dietary additive for commercial aquaculture (Bae et al., 2020). This discussion consists of a summary of the reactions of freshwater and marine fishes to experimental SGS supplementation. Feeding trials have been reported in fresh water species such as rainbow trout (Oncorhynchus mykiss), and juvenile Amur catfish (Silurus asotus), the catadromous Japanese eel (Anguilla japonica), and marine species including olive flounder (Paralichthys olivaceus). Rainbow trout, (O. mykiss) exhibited enhanced weight gain and improved immune status in response to SGS supplemented diets as compared with controls (Won et al., 2017). These increases were comparable to beneficial responses observed in response to other dietary additives, leading the authors to conclude that this mineral supplement has potential applicability as a replacement for antibiotic treatments currently in use. A similar trial of SGS dietary supplementation in juvenile Amur catfish (S. asotus) demonstrated significant growth and immune status enhancements as compared with controls, also suggesting that this mineral feed additive offers an economically appealing option for improved performance in this species (Amoah et al., 2017). Bae et al. (2008) investigated the effects of dietary supplementation of SGS either alone or in combination with a “feed stimulant” in juvenile Japanese eels (Anguilla japonica). These authors reported that the combination treatment produced some beneficial responses including improved growth performances and increased survival rate in response to a challenge with an exogenous pathogen. A study by Oncul et al. (2017) with feeding trials of fermented tuna by-product containing SGS in olive flounder (P. olivaceus) diet, revealed positive effects on non-specific immune responnses such as lysozyme, superoxide dismutase (SOD) and myeloperoxidase (MPO) activities; and enhanced resistance to bacterial infection. Also, Bae et al. (2020) conducted beneficial effects on growth and feed utilization performance, MPO and nitro-blue-tetrazolium (NBT) activity and survival of olive flounder (P. olivaceus) fed low-fishmeal (FM) diets.

These studies revealed a trend favoring enhancements of growth performances and disease resistance in response to SGS treatment, without definitively establishing a mechanism of action. These responses are comparable to enhancements seen in response to oxytetracycline (OTC), and for this reasons SGS is viewed as a possible replacement to antibiotic therapy. Beneficial antibiotic effects have tentatively been attributed to increased nutrient absorption in response to a thinning in the gastrointestinal lining, the decrease in harmful bacteria that otherwise would secrete harmful metabolic by-products, and/or a reduction in nutrient competitiveness between host animals and bacteria (Marshall & Levy, 2011). However, evidence of hazards associated with routine antibiotic use are leading to its elimination in large-scale aquaculture activities (Hernandez-Serrano, 2005; Marshall & Levy, 2011).