Functional significance and physiological regulation of essential trace metals in fish

Trace metals in the teleost fish gill: biological roles, uptake regulation, and detoxification mechanisms

In fish, the gill plays a vital role in regulating the absorption of trace metals and is also highly susceptible to metal toxicity. Trace metals such as iron (Fe), copper (Cu), zinc (Zn), and manganese (Mn) are involved in various catalytic activities and molecular binding within the gill, thereby supporting a range of physiological processes in this organ. While beneficial at normal levels, these metals can become toxic when present in excess. Conversely, nonessential metals like cadmium (Cd) and lead (Pb) can gain entry into gill cells through similar metal transport pathways, potentially interfering with various cellular processes. The transepithelial transport of these metals across the gill epithelium is governed by a variety of metal transport and metal binding proteins. These include the Cu transporter 1 (CTR1), divalent metal transporter 1 (DMT1), and members of the Zrt-/Irt-like protein (ZIP) and zinc transport (ZnT) families. Additionally, some of these metals can compete with major ions (e.g., calcium, sodium) for absorption sites in the gill. This complex crosstalk suggests an interdependent mechanism that balances metal uptake to meet physiological needs while preventing excessive accumulation. In this article, I review the roles of trace metals in proteins/enzymes that support the different functions in the gill of teleost fish. I also discuss current understanding of the pathways involved in regulating the branchial uptake of metals and their influence on ionic regulation, and the potential detoxification mechanisms in the gill. Finally, I summarize knowledge gaps and potential areas for further investigation.

Bioaccumulation of chemical elements in fish from areas affected by oil on the coast of Bahia, Brazil

In 2019, the Brazilian coast was affected by the largest oil spill in its history. We assessed the levels of chemical elements in Lutjanus synagris and Haemulon aurolienatum fish from Itacaré (least affected area), Tinharé-Boipeba (most affected area) and Madre de Deus (chronically affected area). The level of metals differed between species, tissues, life cycle phases, maturation stages and between sampled locations, indicating the influence of biological and environmental aspects on bioaccumulation. Only fish in Madre de Deus showed lead contamination, while arsenic concentrations in the three areas exceeded the maximum value acceptable by Anvisa (National Health Surveillance Agency). It is suggested that the oil spill may have impacted species differently, also having an impact in fish from less affected areas. However, metal concentrations in fish in Madre de Deus stood out when compared to populations in other studied areas.

Illicit Drugs in Surface Waters: How to Get Fish off the Addictive Hook

The United Nations World Drug Report published in 2022 alarmed that the global market of illicit drugs is steadily expanding in space and scale. Substances of abuse are usually perceived in the light of threats to human health and public security, while the environmental aspects of their use and subsequent emissions usually remain less explored. However, as with other human activities, drug production, trade, and consumption of drugs may leave their environmental mark. Therefore, this paper aims to review the occurrence of illicit drugs in surface waters and their bioaccumulation and toxicity in fish. Illicit drugs of different groups, i.e., psychostimulants (methamphetamines/amphetamines, cocaine, and its metabolite benzoylecgonine) and depressants (opioids: morphine, heroin, methadone, fentanyl), can reach the aquatic environment through wastewater discharge as they are often not entirely removed during wastewater treatment processes, resulting in their subsequent circulation in nanomolar concentrations, potentially affecting aquatic biota, including fish. Exposure to such xenobiotics can induce oxidative stress and dysfunction to mitochondrial and lysosomal function, distort locomotion activity by regulating the dopaminergic and glutamatergic systems, increase the predation risk, instigate neurological disorders, disbalance neurotransmission, and produce histopathological alterations in the brain and liver tissues, similar to those described in mammals. Hence, this drugs-related multidimensional harm to fish should be thoroughly investigated in line with environmental protection policies before it is too late. At the same time, selected fish species (e.g., Danio rerio, zebrafish) can be employed as models to study toxic and binge-like effects of psychoactive, illicit compounds.

Excessive dietary iron exposure increases the susceptibility of largemouth bass (Micropterus salmoides) to Aeromonas hydrophila by interfering with immune response, oxidative stress, and intestinal homeostasis

Iron is an essential cofactor in the fundamental metabolic pathways of organisms. Moderate iron intake can enhance animal growth performance, while iron overload increases the risk of pathogen infection. Although the impact of iron on the pathogen-host relationship has been confirmed in higher vertebrates, research in fish is extremely limited. The effects and mechanisms of different levels of iron exposure on the infection of Aeromonas hydrophila in largemouth bass (Micropterus salmoides) remain unclear. In this study, experimental diets were prepared by adding 0, 800, 1600, and 3200 mg/kg of FeSO4∙7H2O to the basal feed, and the impact of a 56-day feeding period on the mortality rate of largemouth bass infected with A. hydrophila was analyzed. Additionally, the relationships between mortality rate and tissue iron content, immune regulation, oxidative stress, iron homeostasis, gut microbiota, and tissue morphology were investigated. The results showed that the survival rate of largemouth bass infected with A. hydrophila decreased with increasing iron exposure levels. Excessive dietary iron intake significantly increased iron deposition in the tissues of largemouth bass, reduced the expression and activity of antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase, increased the content of lipid peroxidation product malondialdehyde, and thereby induced oxidative stress. Excessive iron supplementation could influence the immune response of largemouth bass by upregulating the expression of pro-inflammatory cytokines in the intestine and liver, while downregulating the expression of anti-inflammatory cytokines. Additionally, excessive iron intake could also affect iron metabolism by inducing the expression of hepcidin, disrupt intestinal homeostasis by interfering with the composition and function of the gut microbiota, and induce damage in the intestinal and hepatic tissues. These research findings provide a partial theoretical basis for deciphering the molecular mechanisms underlying the influence of excessive iron exposure on the susceptibility of largemouth bass to pathogenic bacteria.

Metals in species of the Cambeva (Teleostei: Trichomycteridae) genus of the Iguaçu River basin (Brazil)

The population growth is connected to the demand for resources and waste disposal in water. Metals are among several pollutants affecting aquatic ecosystems, posing risks to biota when in high concentrations. Metals can present a great danger to the aquatic ecosystem because they are not degradable and can bioaccumulate. Many rivers are already considered highly polluted. Among them is the Iguaçu River, located in southern Brazil, which is recognized for the Iguaçu Falls and its rate of endemism. One species of the Cambeva genus is among the endemic species found in the Iguaçu River and is threatened with extinction due to anthropization. Thus, we aimed to evaluate and compare the concentrations of copper, zinc, iron, lead, manganese, and cadmium in Cambeva stawiarski and Cambeva sp. 1 in four different streams of the Iguaçu River (Brazil). We collected 20 fish in two municipalities along the Iguaçu River tributaries. The results showed a statistical difference in the metal concentrations in different species and locations, mainly manganese, iron, and copper, observed in both species and municipalities and cadmium, which showed a statistical difference only for C. sp1. Fish from agricultural regions generally had the highest concentrations of metals, some above the permitted limits. Cadmium was found at high concentrations, generating great ecological concern since it is one of the most toxic metals, even in small quantities. The lack of limits in Brazilian legislation makes it challenging to predict the long-term effects of iron.

Metal-amino acid complexes (Zn, Se, Cu, Fe, and Mn) enhance immune response, antioxidant capacity, liver function enzymes, and expression of cytokine genes in Nile Tilapia reared under field conditions

OBJECTIVES

In the present study, we investigated the effects of partial or total replacement of dietary inorganic trace materials (ITM) with metal-amino acid complexes (MAACs) on immune response, antioxidant capacity, cytokine genes expression, and overall health status of Nile Tilapia Oreochromis niloticus reared in in-pond hapas (mesh cages) under field conditions.

METHODS

All-male Nile Tilapia with an average initial weight of about 90 g fish-1 were stocked into the hapas, in quadruplicates, at a density of 60 fish per hapa (30 fish m-3 ). The fish in each hapa were acclimatized to culture conditions and test diets for 1 week. Water quality parameters, including temperature (°C), pH, dissolved oxygen (mg L-1 ), and total ammonia (mg L-1 ), were monitored regularly. The MAACs were formulated to contain the same mineral concentrations found in the inorganic premix. Metal-amino acid complexes replaced the ITM premix at 0 (control), 25, 50, 75, and 100% levels (Table 1). The diets were fed to caged Nile Tilapia twice a day, for 80 days, at a daily rate of 3% of their body weights. The fish were weighed every 10 days, and the daily rations were readjusted. At harvest, fish in each hapa were collected, counted, and weighed collectively. Five fish from each hapa were rapidly anesthetized, and used for chemical and physiological analyses, including antioxidant and immune response analyses, liver function analysis, and gene expression.

RESULT

The activities of lysozyme, respiratory burst (%), alternative complement (ACH50), phagocytic cells, phenoloxidase, superoxide dismutase, glutathione peroxidase, and liver function enzymes were all improved with increasing supplemental MAACs up to the 50% substitution level. The expression of cytokine genes, including interferon, tumor necrosis factor, interleukin-1, serum alkaline phosphatase, the integrated microbial genomes, chloramphenicol acetyltransferase, and transforming growth factor genes, was significantly upregulated in fish fed on MAAC-supplemented diets compared with the control group. The 50% MAAC level produced the highest upregulation of these genes, whereas gene expression decreased with increasing dietary MAAC levels to 75% and 100%. The quadratic regression analysis indicated that about 60-65% MAAC is required for maximum promotion of immunological and oxidative stress responses, gene expression, and overall health status of Nile Tilapia reared in in-pond hapas under field conditions.

CONCLUSION

Replacement of the ITM premix with a MAAC premix enhanced the immune and antioxidant responses of Nile Tilapia.

Essential and non-essential elements in tuna and billfish around the world: Distribution patterns and influencing factors

Tuna and billfish are widely distributed in oceans worldwide. Their survival is relied on a decent share of essential and non-essential elements. We conducted a comprehensive evaluation of essential and non-essential elements in livers of tuna and billfish collected from global oceans. The individual element consistently shown similar orders of magnitude in both tuna and billfish, with essential elements generally being 1-3 orders of magnitude higher than non-essential elements. Various physicochemical properties and behaviors contributed to four distinct clusters of these elements. Also, element distribution pattern indicated the presence of four sample groups based on regions and categories. Nine elements served as characteristic indicators. Among them, fish category was the most important influencing factor. Hg, Fe, Tl, Co, and Se were influenced by body size, trophic level, and feeding habits. Ni was influenced by sampling regions, while Mg, Mn and As were influenced by body size and local primary production.

Metals and Metalloid Concentrations in Fish, Its Spatial Distribution in PPC, Philippines and the Attributable Risks

Fish is an important source of protein in human meals around the world. However, the fish that we are eating may be contaminated with toxicants such as metals and metalloids (MMs), which may pose health risks to consumers. Information on MMs content in fishes and their potential spatial distribution scenarios would provide knowledge to the community to create strategies and protect human health. Hence, this study assessed and determined the health risk levels of MMs in both brackish and marine water fish (BMF) in Puerto Princesa City (PPC), Palawan Province, Philippines. PPC has an existing abandoned open mine pit near the PPC coastline called the "pit lake". The concentrations of As, Ba, Cu, Fe, Mn, Hg, and Zn in fishes were analyzed using portable Olympus Vanta X-ray Fluorescence (pXRF), and the spatial distribution of MMs concentrations in BMF was analyzed using a GIS (geographic information system). Fishes were sampled from fishing boat landing sites and nearby seafood markets. The results revealed that the concentration of MMs in marine fish was generally higher than the brackish water fish. It was recorded that the Hg concentration in marine water fish meat was higher than in brackish water fish meat. The Mn concentration in marine water fish exceeded the permissible limits set by international bodies. An elevated concentration of Mn in BMF was detected across the northern part of PPC, and an elevated concentration of Hg in marine fishes was recorded in the southeast area, where the fish landing sites are located. Ba was also detected in BMF across the southern part of PPC. Moreover, an elevated concentration of Cu was detected in MBF in the northeast and in marine fish in the southeastern area of PPC. Further, this paper elaborates the non-carcinogenic and carcinogenic risks of these fishes to the PPC population and tourists with respect to the MMs content in fish meat.

Metalliferous atmospheric settleable particulate matter action on the fat snook fish (Centropomus parallelus): Metal bioaccumulation, antioxidant responses and histological changes in gills, hepatopancreas and kidneys

Metallic smoke released by steel industries is constitute by a mixture of fine and gross particles containing metals, including the emerging ones, which sedimentation contaminates soil and aquatic ecosystems and put in risk the resident biota. This study determined the metal/metalloids in the atmospheric settleable particulate matter (SePM, particles >10 μm) from a metallurgical industrial area and evaluated metal bioconcentration, antioxidant responses, oxidative stress, and the histopathology in the gills, hepatopancreas and kidneys of fat snook fish (Centropomus parallelus) exposed to different concentrations of SePM (0.0, 0.01, 0.1 and 1.0 g L^-1), for 96 h. From the 27 metals (Al, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, Sn, Ba, La, Ce, W, Hg, Pb, Bi) analyzed, 18 were quantified in SePM and dissolved in seawater. Metal bioconcentrations differed among organs; Fe and Zn were the metals most bioconcentrated in all organs, Fe was higher in hepatopancreas and Zn > Fe > Sr > Al was higher in kidneys. The activity of superoxide dismutase (SOD) decreased in the gills; SOD, catalase (CAT) decreased, and glutathione peroxidase (GPx) increased in hepatopancreas and, CAT, glutathione-S-transferase (GST) and the level of glutathione (GSH) increased in kidneys. The unchanged levels of lipid peroxidation and oxidized protein in any organ indicate that the antioxidant responses were efficient to avoid oxidative stress. Organ lesion indices were higher in the gills > kidneys > hepatopancreas, being higher in fish exposed to 0.01 g L^-1 SePM. All changes indicate a tissue-specific metal/metalloids bioconcentration, antioxidant and morphological responses that all together compromise fish health. Regulatory normative are needed to control the emission of these metalliferous PM to preserve the environment and biota.