Modelling digestive hydrolysis of nutrients in fish using factorial designs and desirability function

Bioaccessibility of plastic-related compounds from polymeric particles in marine settings: Are microplastics the principal vector of phthalate ester congeners and bisphenol A towards marine vertebrates?

Marine vertebrates are known to ingest significant amounts of microplastics (MPs). Once ingested, MPs might cause gastrointestinal injuries and serve as a path of harmful plastic components, such as phthalate esters (PAEs) and bisphenol A (BPA) in the food chain. However, there is a lack of standardized in-vitro methods capable of simulating fish uptake of chemicals from MPs in the environment as potential vectors of such contaminants. In this work, leaching and in-vitro oral bioaccessibility testing of PAEs and BPA from MPs were conducted batchwise using artificial seawater and gut fluids mimicking gastric, intestinal, and gastrointestinal compartments of marine vertebrates at physiological temperature. The environmental and physiologically relevant extraction tests were applied to medium-density polyethylene (PE) and polyvinyl chloride (PVC) certified reference materials containing eight PAEs of varying hydrophobicity, namely, dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate, benzylbutyl phthalate, diethylhexyl phthalate, di-n-octyl phthalate, diisononyl phthalate and diisodecyl phthalate, and BPA (only in PE) as MP surrogates with realistic analyte concentrations of additives for primary MPs. The analysis of the leachates/gut fluid extracts was performed via dilute-and-shoot by ultra-high performance liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Only the most hydrophilic compounds, i.e. DMP, DEP and BPA, were found to get released significantly in saline waters, and exhibited the highest oral bioaccessibility rates (34-83 %). Based on our results, a dual-compartment physiologically relevant gastrointestinal test is recommended for appropriate estimation of fish bioaccessibility. The fish daily intakes of DMP, DEP and BPA from MPs, and seawater ingestion as well were estimated using several contamination scenarios (10th percentile as the low level, 50th percentile as the medium level and 90th percentile as the high level) based on probabilistic distributions and cumulative probability curves of measured environmental concentrations of (i) MPs in seawater throughout the world, (ii) DMP, DEP and BPA in beached MPs and those sampled in the open ocean (including both incurred and adsorbed contaminants), and (iii) DMP, DEP and BPA in seawater as reported in recent literature. Under a medium-level concentration scenario (50th percentile) in marine settings, and taking the gastrointestinal bioaccessibility factor into account, the daily intake of DMP, DEP and BPA from MPs accounted for a mere 0.02 % of the waterborne contribution. Hence, the ingestion of MPs should not be considered the primary route of fish exposure to BPA and the most polar PAEs in marine environments. However, more studies on the local and the global scales for mass concentrations of MPs and additives in marine settings are needed for further confirmation of our findings.

Assessment of Encapsulated Probiotic Lactococcus lactis A12 Viability Using an In Vitro Digestion Model for Tilapia

Probiotics face harsh conditions during their transit through the gastrointestinal tract (GIT) of fish because of low-pH environments and intestine fluid. Therefore, the evaluation of probiotic viability under simulated gastrointestinal conditions is an important step to consider for probiotic supplementation in fish feed prior to in vivo trials. Therefore, this study aimed to evaluate the effect of stomach and intestinal simulated conditions on the viability of encapsulated Lactococcus lactis A12 using an in vitro digestion model for tilapia. A Box Behnken design was used to evaluate the potential effect of three factors, namely stomach pH, residence time in the stomach, and enzyme quantity, on the viability of encapsulated Lactococcus lactis A12. As the main results, low pH (4.00), long residence time (4 h), and enzyme quantity (2.68 U of total protease activity) led to lower final cell counts after the phases of the stomach and intestine. Encapsulated probiotic bacteria showed higher viability (p < 0.05) and antibacterial activity (p < 0.05) against the pathogen Streptococcus agalactiae than non-encapsulated bacteria. The results suggest that L. lactis A12 survives in GIT conditions and that the proposed in vitro model could be used to explore the viability of probiotic bacteria intended for fish feed supplementation.

First insights into the activity of major digestive enzymes in the intestine of the European catfish Silurus glanis and protective anti-enzymatic potential of its gut parasite Silurotaenia siluri

The European catfish Silurus glanis is attracting growing interest as an object of fisheries and aquaculture, which is reinforced by the expansion of its natural range under climate change. Shaping the effective exploitation strategy for this valuable species requires detailed knowledge of its biology, including feeding and digestion processes, especially near the natural limits of the species range. Meanwhile, the digestion physiology of the European catfish remains poorly explored, including the activity of major digestive enzymes and the possible effect of intestinal parasites on this activity. In this regard, the activity of proteinases and α-amylase in the intestinal mucosa of the catfish was studied. Adult catfish were collected in the Rybinsk reservoir (Upper Volga) located close to the northern limit of the species range. It was shown that all subclasses of intestinal digestive proteinases, including serine proteinases, metalloproteases and cysteine (thiol) proteinases, function in the gut mucosa of the catfish. The mucosal levels of total proteolytic activity depended on fish size, in contrast to those of trypsin, chymotrypsin and α-amylase. The level of chymotrypsin activity was significantly higher than that of trypsin activity. It was also found that the incubation medium and extract of the cestodes Silurotaenia siluri parasitizing the catfish gut had a significant inhibitory effect on the activity of serine proteases (trypsin and chymotrypsin) operating in the intestines of the host fish.

pH-Responsive Chitosan-Doped ZnO Hybrid Hydrogels for the Encapsulation of Bioactive Compounds in Aquaculture

In this study, we synthesized and characterized pH-responsive Chitosan-AgCl-doped ZnO hybrid hydrogels and evaluated their potential for loading aquaculture bioactive compounds, and assessed their antimicrobial properties against a threatening pathogen associated with disease across a broad spectrum of warm water fish and invertebrates. Hydrogel characterization consisted of assessing morphology via SEM, composition via EDS, hydrogels' network components interactions via FT-IR and pH response through swelling behavior determinations. The swelling characterization of the synthesized hydrogels demonstrated a pH-responsive behavior, showing that low pH values caused the hydrogel polymeric network to expand and capture more of the aqueous solution. These characteristics make the synthesized hydrogels suitable for the encapsulation and controlled release of drugs and bioactive compounds in aquaculture. Chitosan_ZnO hybrid hydrogels showed great antimicrobial activity against Vibrio harveyi, even better than that of loaded PB hydrogels. Here, we provide evidence for the potential capacity of Chitosan_ZnO hybrid hydrogels for the preventive and curative treatment of diseases that impact aquaculture animal health and prevent drug resistance by bacteria.

Oral administration of wild plant-derived minerals and red ginseng ameliorates insulin resistance in fish through different pathways

Many kinds of fish are characterized by a limited efficiency to use carbohydrates. For this reason, raw fish and mixed feed containing a lot of fish meal have been used as feed for fish farming. However, continuing to use high-protein diets not only increases the cost of fish farming, but may also fuel animal protein shortages. Furthermore, carbohydrates are added to improve the texture of the feed and act as a binding agent and are usually contained at 20% in the feed. It makes sense, therefore, to find ways to make good use of carbohydrates rather than wasting them. The physiological mechanisms of glucose intolerance in fish are not yet well understood. Therefore, we investigated the glucose utilization of fish, omnivorous goldfish Carassius auratus and carnivorous rainbow trout Oncorhynchus mykiss. Furthermore, the effects of oral administration of wild plant-derived minerals and red ginseng on the glucose utilization in these fish muscle cells were investigated. As a result, we found the following. (1) An extremely high insulin resistance in fish muscle and the symptom was more pronounced in carnivorous rainbow trout. (2) Administration of wild plant-derived minerals promotes the translocation of the insulin-responsive glucose transporter GLUT4 to the cell surface of white muscle via activation of the PI3 kinase axis, whereas administration of red ginseng not only promotes GLUT4 transfer and translocation to the cell surface of white muscle via AMPK activation as well as promoting glucose uptake into muscle cells via a pathway separate from the insulin signaling system. (3) In fish, at least goldfish and rainbow trout, both PI3K/Akt and AMPK signaling cascades exist to promote glucose uptake into muscle cells, as in mammals.

In-vitro digestion models: a critical review for human and fish and a protocol for in-vitro digestion in fish

Digestive systems in human, animals, and fish are biological reactors and membranes to digest food and extract nutrients. Therefore, static and dynamic models of in-vitro digestion systems are developed to study e.g. novel food and feed before in-vivo studies. Such models are well developed for human, but not to the same extent for animals and fish. On the other hand, recent advances in aquaculture nutrition have created several potential fish meal replacements, and the assessment of their nutrient digestibility is critical in the application as a fish meal replacement. Using an in-vitro method, the assessment of an ingredient digestibility could be faster and less expensive compared to using an in-vivo experiment. An in-vitro method has been widely used to assess food nutrient digestibility for humans; however, its application for fish is still in the early stages. Both the human and fish as monogastric vertebrates share similar gastrointestinal systems; thus, the concept from the application for humans could be applied for fish. This review aims to improve the in-vitro digestion protocol for fish by adapting the concept from then study for humans, summarizing the current available in-vitro digestion model developed for human and fish in-vitro digestion study, identifying challenges specifically for fish required to be tackled and suggesting an engineering approach to adapt the human in-vitro gastrointestinal model to fish. Protocols to conduct in-vitro digestion study for fish are then proposed.

Solid-state fermented brewer's spent grain enzymatic extract increases in vitro and in vivo feed digestibility in European seabass

Brewer's spent grain (BSG) is the largest by-product originated from the brewery industry with a high potential for producing carbohydrases by solid-state fermentation. This work aimed to test the efficacy of a carbohydrases-rich extract produced from solid-state fermentation of BSG, to enhance the digestibility of a plant-based diet for European seabass (Dicentrarchus labrax). First, BSG was fermented with A. ibericus to obtain an aqueous lyophilized extract (SSF-BSG extract) and incorporated in a plant-based diet at increasing levels (0-control; 0.1%, 0.2%, and 0.4%). Another diet incorporating a commercial carbohydrases-complex (0.04%; Natugrain; BASF) was formulated. Then, all diets were tested in in vitro and in vivo digestibility assays. In vitro assays, simulating stomach and intestine digestion in European seabass, assessed dietary phosphorus, phytate phosphorus, carbohydrates, and protein hydrolysis, as well as interactive effects between fish enzymes and dietary SSF-BSG extract. After, an in vivo assay was carried out with European seabass juveniles fed selected diets (0-control; 0.1%, and 0.4%). In vitro digestibility assays showed that pentoses release increased 45% with 0.4% SSF-BSG extract and 25% with Natugrain supplemented diets, while amino acids release was not affected. A negative interaction between endogenous fish enzymes and SSF-BSG extract was observed in both diets. The in vivo digestibility assay corroborated in vitro data. Accordingly, the dietary supplementation with 0.4% SSF-BSG increased the digestibility of dry matter, starch, cellulose, glucans, and energy and did not affect protein digestibility. The present work showed the high potential of BSG to produce an added-value functional supplement with high carbohydrases activity and its potential contribution to the circular economy by improving the nutritional value of low-cost and sustainable ingredients that can be included in aquafeeds.

The synthesis of lipids and proteins in vitro in tissues of Cyprinus carpio infected with Bothriocephalus acheilognathi

The problem of the mechanisms of regulation of biochemical processes in carp Cyprinus carpio (Linnaeus, 1758) tissues and organs caused by infection with Bothriocephalus (Schyzocotyle) acheilognathi (Yamaguti, 1934) at different intensities of invasion remains practically unstudied. The purpose of this study was to dedetrmine the intensity of lipid and protein synthesis in vitro when [6-14C]glucose and [2-14C]lysine are used as their precursor in the tissues of the intestine, hepatopancreas and skeletal muscles of carp. The study was conducted on this-year carp with body weight 14.5–20.5 g, at different invasion rates of the helminth B. acheilognathi, which belongs to the family Bothriocephalidae of the Pseudophyllidae order of the Cestoda class of the Plathelminthes phylum. The examined carp were divided into three groups: 1st group of fish was free from intestinal helminths of B. acheilognathi (control); 2nd group of fish was weakly infected with helminths (intensity of invasion was 1–3 helminths per fish); the 3rd group of fish was highly infected (the invasion intensity was 4 worms and more per fish). Our results showed that in fish infected with the helminth B. acheilognathi in comparison to uninfected, the intensity of lipid synthesis in the intestinal wall, hepatopancreas, skeletal muscle was much lower when [6-14C]glucose was used as a predecessor than when [2-14C]lysine was used as a predecessor. In the examined tissues, significant decrease was observed in the synthesis of reserve lipids (mono-, di- and triacylglycerols) in comparison to the structural (phospholipids and cholesterol), which depends on the intensity of the B. acheilognathi invasion. In the metabolic processes in the wall of the intestine, hepatopancreas, skeletal muscle of this-year carp infectd with B. acheilognathi helminths, under in vitro conditions, [6-14C]glucose was used more than [2-14C]lysine. The intensity of protein synthesis in the intestinal wall, hepatopancreas, skeletal muscles of this-year carp infected with the helminth B. acheilognathi under in vitro conditions increased when [6-14C]glucose was added to the incubation medium, on average 7.1–28.3% and decreased when [2-14C]lysine was added, on average 7.8–25.7%.