Effects of salinity and copper co-exposure on copper bioaccumulation in marine rabbitfish Siganus oramin

De Novo Assembly, Characterization, and Comparative Transcriptome Analysis of Mature Male and Female Gonads of Rabbitfish (Siganus oramin) (Bloch & Schneider, 1801)

The rabbitfish, Siganus oramin, is a commercially important table fish in southeastern China. However, there have been few studies on its gonad development and reproduction regulation. Comparative transcriptome analysis was first performed on adult male and female gonads of S. oramin. In total, 47,070 unigenes were successfully assembled and 22,737 unigenes were successfully annotated. Through comparative transcriptome analysis of male and female gonads, a total of 6722 differentially expressed genes were successfully identified, with 3528 upregulated genes and 3154 downregulated genes in the testes. In addition, 39 differentially expressed reproduction-related genes were identified. Finally, quantitative real-time PCR was used to validate the expression levels of several differentially expressed genes. These results provide important data for further studying the function of reproduction-related genes and the molecular mechanism regulating gonad development and reproduction in S. oramin.

A comprehensive review of the effects of salinity, dissolved organic carbon, pH, and temperature on copper biotoxicity: Implications for setting the copper marine water quality criteria

In recent years, there has been a growing concern about the ecological hazards associated with copper, which has sparked increased interest in copper water quality criteria (WQC). The crucial factors affecting the bioavailability of copper in seawater are now acknowledged to be salinity, dissolved organic carbon (DOC), pH, and temperature. Research on the influence of these four water quality parameters on copper toxicity is rapidly expanding. However, a comprehensive and clear understanding of the relevant mechanisms is currently lacking, hindering the development of a consistent international method to establish the seawater WQC value for copper. As a response to this knowledge gap, this study presents a comprehensive summary with two key focuses: (1) It meticulously analyzes the effects of salinity, DOC, pH, and temperature on copper toxicity to marine organisms. It takes into account the adaptability of different species to salinity, pH and temperature. (2) Additionally, the study delves into the impact of these four water parameters on the acute toxicity values of copper on marine organisms while also reviewing the methods used in establishing the marine WQC value of copper. The study proposed a two-step process: initially zoning based on the difference of salinity and DOC, followed by the establishment of Cu WQC values for different zones during various seasons, considering the impacts of water quality parameters on copper toxicity. By providing fundamental scientific insights, this research not only enhances our understanding and predictive capabilities concerning water quality parameter-dependent Cu toxicity in marine organisms but also contributes to the development of copper seawater WQC values. Ultimately, this valuable information facilitates more informed decision-making in marine water quality management efforts.

Systematic toxicological analysis of the effect of salinity on the physiological stress induced by triphenyltin in Nile tilapia

Triphenyltin (TPT), a synthetic chemical, is prevalent in complex salinity areas, including estuaries and coastal regions. However, current studies on the toxicological effects of TPT relevant to the environment at different salinities are limited. In the study, biochemical, histological, and transcriptional analyses of TPT and salinity alone, or in combination, was performed on the Nile tilapia (Oreochromis niloticus) liver. Nile tilapia exhibited weakened antioxidant defenses and liver damage. Transcriptomic analysis revealed that TPT exposure primarily affected lipid metabolism and immunity; salinity exposure alone particularly affected carbohydrate metabolism; combined exposure primarily immune- and metabolic-related signaling pathways. In addition, the single exposure to TPT or salinity induced inflammatory responses by up-regulating the expression of pro-inflammatory cytokines, whereas combined exposure suppressed inflammation by down-regulating pro-inflammatory cytokine levels. These findings are beneficial to understand the negative effects of TPT exposure in Nile tilapia in the broad salinity zones and its potential defense mechanisms.

Effect of trace metal contamination in sediments on the bioaccumulation of bivalve Meretrix meretrix

A quinquennial seasonal study (2015-2019) has been conducted to evaluate the bioaccumulation pattern of trace metals in Meretrix meretrix. The concentration of trace metals in the clam was observed as Cr > Cu > Ni > Zn > Pb > Cd > Hg, (Body> Mantle > Gills), similar to sediments. Contamination Factor of Cu and Cr in sediments showed strong association with the corresponding metal concentration in the body (r = 0.687, r = 0.962), mantle (r = 0.880, r = 0.956) and gills (r = 0.937, r = 0.863). Bioconcentration Factor was high for Cr followed by Ni. Mean Metal Concentration Rate (MMCR) of Cr was high and Hg was low (Body>Mantle>Gills). Our study establishes that the trace metal intake by Meretrix meretrix is associated with seasonal variation, physicochemical factors, sediment texture, chemical speciation and the metabolic stress created within the species induced from increased demand for protein synthesis. The latter resulted in the augmented rate of accumulation of Cu and Cr.

RETROSPECTIVE REVIEW OF COPPER SULFATE IMMERSION TREATMENT IN MARINE TELEOSTS DURING QUARANTINE AT THE NATIONAL AQUARIUM OF BALTIMORE FROM 2004 TO 2016

Copper sulfate immersion is common for the prevention and treatment of Cryptocaryon irritans during quarantine of marine teleosts. The National Aquarium in Baltimore has followed a consistent copper sulfate protocol for marine teleost quarantine since 2004. The protocol used copper sulfate pentahydrate as a slow drip to increase copper ions over 3-5 days to a level of 0.18-0.21 mg/L. This level was maintained for 21 days, and then copper ions were rapidly removed with activated carbon filtration and water changes. Quarantine records from 2004-2016 were used to examine mortality of marine teleosts during copper treatment and identify factors that might have influenced mortality. The following records were excluded: brackish and freshwater teleosts (salinity <25 g/L); long-term treatment at subtherapeutic levels (<0.18 mg/L); intentional short courses (<14 days); and use outside of quarantine. Species, system volume, temperature, parasitic outbreaks, concurrent medications, and water quality concerns were evaluated. During this period, 4,835 individual teleosts belonging to 347 different species were treated. From 2004 to 2016, mortality during copper treatment was 4.1% (199/4,835 individuals) and was higher when treatment was started during the first week of quarantine (7.7%, 68/884) rather than later (3.3%, 131/3,951 individuals). Of the mortalities, 24.1% (48/199) occurred during the initial subtherapeutic period, and 75.9% (151/199) occurred during the therapeutic period. No mortalities occurred in 75.5% (262/347) of species during copper treatment. When using a similar methodology, copper sulfate is a safe immersion for quarantine of marine teleosts. Mortalities during copper treatment can be reduced by increasing copper ion levels to therapeutic ranges more slowly (e.g., over 7 days) and starting copper treatment after the first week of quarantine.

Trophic transfer of trace elements in a euryhaline fish, the turbot Scophthalmus maximus: Contrasting effects of salinity on two essential elements

Trace elements can be accumulated from coastal environment by aquatic organisms from their food and be transferred throughout the food webs. Studying the effects of salinity on the trophic transfer of trace elements in a euryhaline fish, able to deal with large variations in salinity, is therefore key to understand their dynamics in aquatic environments. In this context, we investigated the potential influence of salinity on the trophic transfer of two essential elements (Mn and Zn) in the euryhaline fish, the turbot Scophthalmus maximus using radiotracer techniques. After acclimation to three salinities (10, 25 and 38), turbots were fed with radiolabelled pellets (⁵⁴Mn and ⁶⁵Zn). Kinetic parameters of depuration were determined after a 21-d period and trophic transfer factors were calculated. Trophic transfer of Mn at the highest salinity was significantly lower than for the other conditions whereas salinity did not significantly influenced Zn trophic transfer. Differences in the processes involved in the regulation (homeostasis) of the two tested trace elements may explain the contrasting influence of seawater salinity for Mn and Zn.

Performance of biomarkers metallothionein and ethoxyresorufin O-deethylase in aquatic environments: A meta-analytic approach

The preservation of natural environments guarantees the conservation of biodiversity and ecosystem processes. Biomonitoring programs in preserved sites can be carried out using molecular biomarkers, which reflect possible stresses that exist in the monitored location. The metallothionein (MT) proteins and isoenzyme Cytochrome P4501A (CYP4501A) are among the most used biomarkers and reflect the detoxification of metal and organic xenobiotics, respectively. This study aimed to assess the performance of these biomarkers in natural aquatic environments using a meta-analytic approach. The data search was conducted in ISI Web of Science™, considering papers published until August 2016. Studies included in this research needed to compare reference or control sites and sites under stress and be conducted in situ. In general, both biomarkers were useful when comparing control sites with sites under stress. Moreover, when the data were categorized into groups of organisms, mainly bivalves and fishes, there were differences between the groups and between the monitored environments, marine or freshwater. The use of these biomarkers in fish is suitable for freshwater environments, and bivalves are suitable for marine environments. We concluded that the concomitant use of vertebrate and invertebrate bioindicators is useful to develop an effective biomonitoring program and to avoid biases due the physiology of the selected bioindicator.

Copper bioaccumulation and biokinetic modeling in marine herbivorous fish Siganus oramin

Marine herbivorous fish directly consume macroalgae, which commonly accumulate high levels of trace metals in polluted areas. We proposed that herbivorous fish could be better candidates for biomonitoring marine metal pollution than carnivorous fish. To date, the trophic transfer of Cu from macroalgae to marine herbivorous fish is unclear. In this study, the kinetics of Cu bioaccumulation in a widespread marine herbivorous fish, Siganus oramin, were investigated, and biokinetic modeling was applied to estimate the Cu levels in the fish sampled from different sites and seasons. The results showed that Cu accumulation in the fish was linearly correlated to the dietary Cu levels in the different prey species, which were proportional to the waterborne Cu concentrations. The Cu found in the subcellular trophically available metal fraction (TAM) in the prey contributed the largest proportion of accumulated Cu in S. oramin. The dietary assimilation efficiencies (AEs) of Cu were 15.56 ± 1.76%, 13.42 ± 2.86%, and 21.36 ± 1.47% for Ulva lactuca, Gracilaria lemaneiformis and Gracilaria gigas, respectively. The calculated waterborne uptake rate constant (k_u) of Cu was 0.023 ± 0.011 L g^-1 d^-1, and the efflux rate constant (k_e) was 0.055 ± 0.021 d^-1. Dietary Cu accounted for 60%-75% of the body Cu in S. oramin, suggesting that dietary uptake could be the primary route for Cu bioaccumulation in herbivorous fish. The biokinetic model demonstrated that the Cu concentrations in the water and fish presented a positive linear relationship, which was in line with our field investigation along the coastal areas of South China. Therefore, we suggested that S. oramin could be used as a biomonitoring organism for Cu pollution in the marine environment. However, the heterogeneities between the predicted levels and the measured levels of Cu implied that seasonal changes should be taken into account to improve the accuracy of the model.