The incorporation of strontium and barium into the otoliths of the flounder Paralichthys olivaceus at early life stages demonstrates resilience to ocean acidification.

Ocean acidification could modify the bioavailability and chemical properties of trace elements in seawater, which could affect their incorporation into the calcareous structures of marine organisms. Fish otoliths, biomineralized ear stones made by aragonite, are suspended within the endolymph fluid of teleosts, indicating that the elemental incorporation of otoliths might also be susceptible to ocean acidification. In this study, we evaluated the combined effects of CO2-induced ocean acidification (pH 8.10, 7.70, and 7.30, corresponding to ocean acidification scenarios under the representative concentration pathway 8.5 model as projected by the Intergovernmental Panel on Climate Change) and water elemental concentrations of strontium (Sr) and barium (Ba; low, medium, and high) on elemental incorporation into otoliths of the flounder Paralichthys olivaceus at early life stages. Our results revealed that the elemental incorporation of Sr and Ba into otoliths was principally dependent on the corresponding water elemental concentrations rather than on ocean acidification. Moreover, the partition coefficients (DMe) of Sr and Ba may stabilize after dynamic equilibrium is reached as the water elemental concentration increases, but are not affected by ocean acidification. Therefore, the incorporation of Sr and Ba into otoliths of the flounder at early life stages may not serve as an effective indicator of ocean acidification. In other words, the findings suggest that ocean acidification does not impact the incorporation of Sr and Ba incorporation into otoliths when tracing the temperature or salinity experiences of the flounder. Our findings will provide new knowledge for understanding the potential ecological effects of ocean acidification on the recruitment dynamics of fish species.

Interactive impacts of CO2-induced seawater acidification and cadmium exposure on antioxidant defenses of juvenile tongue sole Cynoglossus semilaevis.

Antioxidant responses of juvenile sole exposed to seawater acidification (SA) and Cd were investigated. SA increased lipid peroxidation (LPO) in the fish, independent of Cd concentrations. Cd at medium and high levels inflated LPO under no or moderate SA conditions. This effect was absent under high SA levels, due to SA effect exceeding and obscuring Cd effect. SA and Cd collaborated to provoke LPO, with SOD and CAT being stimulated to defend against oxidative stress, while those related to GSH redox cycle were inhibited under SA exposure. Responses of GSH-related antioxidants to Cd impact varied contingent on their interactions with SA. This defensive strategy was insufficient to protect fish from increased LPO. Antioxidants responded more sensitively to SA than Cd exposure. GSH, GR, SOD and CAT are sensitive biomarkers for SA conditions. The findings offer insights into assessing fish's antioxidant defense strategy under Cd and SA circumstances in natural habitats.

Ocean acidification induces tissue-specific interactions with copper toxicity on antioxidant defences in viscera and gills of Asiatic hard clam Meretrix petechialis (Lamarck, 1818).

Toxicity of contaminants in organisms under ocean acidification (OA) has attracted increasing attention in ecotoxicological studies. This study investigated how pCO2-driven OA affected waterborne copper (Cu) toxicity in antioxidant defences in viscera and gills of Asiatic hard clam Meretrix petechialis (Lamarck, 1818). Clams were continuously exposed to Cu at ambient relevant (0/no metal exposure, 10 and 50 µg L-1) and polluted-high (100 µg L-1) concentrations in unacidified (pH 8.10) and acidified (pH 7.70/moderate OA and 7.30/extreme OA) seawater for 21 days. Following coexposure, metal bioaccumulation and responses of antioxidant defence-related biomarkers to OA and Cu coexposure were investigated. Results showed that metal bioaccumulation was positively correlated with waterborne metal concentrations but was not notably influenced by OA conditions. Both Cu and OA affected the antioxidant responses to environmental stress. Additionally, OA induced tissue-specific interactions with Cu on antioxidant defences, varying with exposure conditions. In unacidified seawater, antioxidant biomarkers were activated to defend against oxidative stress induced by Cu and prevented clams from lipid peroxidation (LPO or MDA), but failed to defend against DNA damage (8-OHdG). OA exacerbated Cu toxicity in antioxidant defences and increased LPO levels in tissues. Gills and viscera adopted adaptive antioxidant defence strategies to manage oxidative stress, with the former being more vulnerable to oxidative stress than the latter. MDA and 8-OHdG were sensitive to OA and Cu exposure, respectively, and were useful bioindicators for assessing oxidative stress. Integrated biomarker response (IBR) and PCA can reflect the integrative responses of antioxidant biomarkers to environmental stress and illuminate the contributions of specific biomarkers to antioxidant defence strategies. The findings provided insights for understanding antioxidant defences against metal toxicity in marine bivalves under OA scenarios, which is essential into managing wild populations.

pCO2-driven seawater acidification affects aqueous-phase copper toxicity in juvenile flounder Paralichthys olivaceus: Metal accumulation, antioxidant defenses and detoxification in livers.

Ocean acidification potentially influences the biotoxicity of metals and the antioxidant defense systems of marine organisms. This study investigated how pCO2-driven seawater acidification (SA) affected aqueous-phase copper (Cu) toxicity in the juvenile flounder Paralichthys olivaceus from the perspective of hepatic oxidative stress and damage to better understand the mechanisms underlying the biological effects produced by the two stressors. Fish were exposed to aqueous-phase Cu at relevant ambient and polluted concentrations (0, 5, 10, 50, 100 and 200 µg L-1) at different pH levels (no SA: pH 8.10; moderate SA: pH 7.70, pCO2 ∼1353.89 µatm; extreme SA: pH 7.30, pCO2 ∼3471.27 µatm) for 28 days. A battery of biomarkers in the livers was examined to investigate their roles in antioxidant defense and detoxification in response to coexposure. Hepatic Cu accumulation (30.22-184.90 mg kg-1) was positively correlated with Cu concentrations. The biomarkers responded adaptively to different redox states following SA and Cu exposure. In unacidified seawater, increases in Cu concentrations significantly induced hepatic lipid peroxidation (LPO, by up to 27.03 %), although compensatory responses in antioxidant defenses and detoxification were activated. Moderate SA helped maintain hepatic redox homeostasis and alleviated LPO through different defense strategies, depending on Cu concentrations. Under extreme SA, antioxidant-based defenses were activated to cope with oxidative stress at ambient-low Cu concentrations but failed to defend against Cu toxicity at polluted Cu levels, and LPO (by up to 63.90 %) was significantly induced. Additionally, thiols (GSH and MT) responded actively to cope with Cu toxicity under SA. SOD, CAT, EROD, and GST were also sensitively involved in defending against hepatic oxidative stress during coexposure. These findings highlight the notable interactive effects of SA and Cu and provide a basis for understanding antioxidant-based defenses in marine fish confronting environmental challenges.

Microplastic pollution in the environment and organisms of Xiangshan Bay, East China Sea: An area of intensive mariculture.

Microplastic (MP) pollution in oceans is an emerging environmental problem that poses ecological risks for marine ecosystems. Based on the abundance, distribution, and characteristics of microplastics (MPs) in surface water, sediment, and organisms, MP sources, pollution, trophic transfer, and ecological risk in Xiangshan Bay, an area of intensive mariculture in East China Sea, were assessed in this study. MPs were prevalent in the environment and organisms, with overall abundances at a low-medium level compared with the levels in the coastal areas. In water, MPs were more abundant in the inner bay (0.32 items m-3), which is a more significant source of MPs with intensive mariculture than the central (0.09 items m-3) and outer bays (0.07 items m-3). The narrow and land-enclosed inner bay, with weak hydrodynamics for water exchange, retained MPs, thus increasing their abundance. The ecological risk of MPs in water was at a low-moderate level. The MP abundance in sediment did not vary significantly among the three regions of the bay. The morphological characteristics and polymers of the MPs differed in sediment from those in water, which was related to their diverse environmental redistribution routes. MP abundance ingested by organisms were related to their biological features and foraging habits. Overall, fish ingested more MPs than crustaceans, bivalves, and cephalopods, while zooplankton ingested the minimal MPs. Filter feeders ingested less MPs, with a preference for smaller particles than predators. MPs did not show trophic transfer behavior in organisms. Additionally, MPs ingested by infauna showed similar morphological and chemical characteristics compared to sediment at the point of organism residence, whereas MPs ingested by pelagic species were dissimilar to those in surface water. Our findings provide information for understanding MP pollution, source tracing, trophic transfer, and ecological risk assessment in coastal ecosystems.

Toxicological effects of cadmium on the immune response and biomineralization of larval flounder Paralichthys olivaceus under seawater acidification.

Seawater acidification can cause threats to both calcifying and uncalcifying marine organisms, affecting their acid-base regulatory functions, immune system and biomineralization. Marine pollutants, such as cadmium (Cd) that is globally distributed in coastal ecosystems, do not affect organisms alone but commonly as combined stressors. To investigate the toxicological effects of Cd on the immune and biomineralization of marine fishes under seawater acidification, flounder Paralichthys olivaceus was exposed to seawater acidification (control (pH 8.10), 7.70 and 7.30) and Cd exposure (control (0.36 µg L-1), 0.01 and 0.15 mg L-1 Cd) for 49 days from embryonic stage until they became settled. Immune and biomineralization-related biomarkers of flounder at the end of exposure were investigated. Results showed that single seawater acidification and Cd exposure or combined exposure significantly affected the immune system-related enzyme activities. Specifically, lysozyme (LZM) activity was significantly inhibited by single seawater acidification and Cd exposure, indicating innate immunosuppression under two stressors. Contents of IgM, HSP70 and MT were induced by seawater acidification or Cd exposure, indicating a detoxification mechanism that responded to the stressors. The expressions of immune-related genes were upregulated (hsp70 and mt) or downregulated (lzm) under Cd exposure. Of the biomineralization-related enzymes, activities of carbonic anhydrase (CA), Na+/K+-ATPase and Ca2+-ATPase increased under seawater acidification and Cd exposure, a potential mechanism in response to changes of acid-base balance induced by the stressors. Generally, immune and biomineralization of the flounder responded more sensitively to Cd exposure than seawater acidification. Seawater acidification aggravated the toxicological effects of Cd exposure on the two physiological functions, while high Cd exposure augmented their responses to seawater acidification.

Assessment of plastic pollution in the Bohai Sea: Abundance, distribution, morphological characteristics and chemical components.

Plastics are globally distributed in oceans and can pose a threat to the environment and organisms. In this study, plastic pollution in surface water and sediments of the Bohai Sea was assessed based on plastic abundance, distribution and characteristics (shape, polymer, size and color). Water and sediment samples were collected across the sea using a plankton net (330 µm) and a grab sampler, respectively. The following conclusions were reached. 1) In surface water, large plastics were less abundant (0.14 items/m3) and showed less diverse characteristics than microplastics (0.79 items/m3) but did not significantly differ in spatial distribution. 2) Microplastics in water were more abundant (1.95 items/m3) with more diverse characteristics in Liaodong Bay than in other regions of the sea (0.26-0.59 items/m3). Plastic waste from highly concentrated agricultural, industrial and fishery activities could make large contributions to microplastics in Liaodong Bay. Additionally, low hydrodynamics and long distance to Bohai Strait are unfavorable for diffusion of particles, facilitating the retention of microplastics and increasing the abundance in this bay. 3) Microplastics in sediments were smaller in terms of dominant sizes (<0.5 mm) with less diverse characteristics than particles in water (0.5-1.5 mm). Specifically, fragments, foams and lines dominated among the microplastics in water, whereas fibers and fragments were dominant particles in sediments; alkyd resin, polyethylene, polystyrene and polypropylene (PP) predominated among the particles in water, but rayon, cellulose and PP were dominant particles in sediments. 4) Neither abundance nor size of microplastics in the two media was proportionally correlated and showed low similarity indexes of polymer (0.16), shape (0.29) or color (0.38). This could be related to mismatch in spatiotemporal distributions and variations in the characteristics, fate and behavior of microplastics in the two media. The findings provide knowledge for tracing the sources of plastics in the Bohai Sea.

Tissue-Specific Accumulation and Antioxidant Defenses in Flounder (Paralichthys olivaceus) Juveniles Experimentally Exposed to Methylmercury.

Methylmercury (MeHg) is the most toxic form of mercury and can accumulate in the cells of marine organisms, such as fish, causing adverse effects on various physiological functions. This study examined MeHg accumulation and its toxicological role in antioxidant defenses in tissues, including the liver, gills, and muscle of flounder (Paralichthys olivaceus) juveniles. After 30 d of MeHg exposure (0, 0.1, 1.0, 10.0, and 20.0 µg L-1), the accumulation of MeHg in the three tissues correlated positively with the concentration of MeHg and exhibited tissue specificity in the order of liver > gills > muscle. Among the antioxidant markers, the activities of SOD (superoxide dismutase) and GST (glutathione S-transferase) as well as the content of glutathione (GSH) in the liver and gills were induced at 0.1-10.0 µg L-1 but repressed at 20.0 µg L-1. The activities of SOD and GST and the content of GSH in the muscle significantly increased with increasing MeHg concentration. Catalase (CAT) activity in the liver was induced at 0.1-1.0 µg L-1 but inhibited at 10.0-20.0 µg L-1, whereas exposure to MeHg did not remarkably affect CAT activity in the gills and muscle. The levels of lipid peroxidation (LPO) increased dose dependently, showing tissue specificity with the highest level in the liver, then the gills, followed by muscles. Overall, higher sensitivity to oxidative stress induced by MeHg was detected in the liver than the gills and muscle. These findings improve our understanding of the tissue-specific accumulation of heavy metals and their roles in antioxidant responses in marine fish subjected to MeHg exposure.

Effects of seawater acidification and cadmium on the antioxidant defense of flounder Paralichthys olivaceus larvae.

Increasing atmospheric carbon dioxide has led to a decrease in the pH of the ocean, which influences the speciation of heavy metals and consequently affects metal toxicity in marine organisms. To investigate the effects of seawater acidification and metals on the antioxidant defenses of marine fishes, the flounder Paralichthys olivaceus, was continuously exposed to cadmium (Cd; control, 0.01 and 0.15 mg L-1) and acidified seawater (control (pH 8.10), 7.70 and 7.30) for 49 days from embryogenesis to settlement. The results demonstrated that both Cd and acidified seawater could induce oxidative stress and consequently cause lipid peroxidation (LPO) in the larvae. Antioxidants (i.e., superoxide dismutase, SOD; catalase, CAT; reduced glutathione, GSH; glutathione S-transferase, GST; glutathione peroxidase, GPx; and glutathione reductase, GR) functioned to defend the larvae against oxidative damage. Overall, Cd induced (SOD, GST and GSH) or inhibited (CAT and GPx) the enzymatic activities or contents of all the selected antioxidants except for GR. The antioxidants responded differently to seawater acidification, depending on their interaction with the metal. Similarly, the mRNA expressions of the antioxidant-related genes were upregulated (sod, gr and gst) or downregulated (cat and gpx) in response to increasing Cd exposure. Seawater acidification did not necessarily affect all of the biomarkers; in some cases (e.g., SOD and sod, GR and gr), Cd stress may have exceeded and masked the stress from seawater acidification in regulating the antioxidant defense of the larvae. The integrated biomarker response (IBR) was enhanced with increasing levels of the stressors. These findings support the hypothesis that seawater acidification not only directly affects the antioxidant defense in flounder larvae but also interacts with Cd to further regulate this defense. This study has ecological significance for assessing the long-term impacts of ocean acidification and metal pollution on the recruitment of fish populations in the wild.

Biomagnification of methylmercury in a marine food web in Laizhou Bay (North China) and associated potential risks to public health.

The concentrations of total mercury (THg) and methylmercury (MeHg) were assessed in water, sediment and biota (54 species) samples from the coast of Laizhou Bay, to evaluate MeHg biomagnification in Laizhou Bay food web. The trophic web structure was determined with stable isotope ratios. The MeHg concentrations were highly variable among species ranged from 4.8 ng g-1 in primary producers to 411.2 ng g-1 in spotted sea bass. Weight and ecotype were the principal parameters related to the mercury concentrations for most species. The trophic magnification factors (TMFs) for MeHg and THg were 2.09 and 1.69, respectively, indicating that mercury biomagnification is occurring in this marine food web. The estimated weekly intake (EWI) and target hazard quotient (THQ) values demonstrated that consuming predatory fishes from the bay could cause potential health risks to humans.

Antioxidant defenses and immune responses of flounder Paralichthys olivaceus larvae under methylmercury exposure.

Methylmercury (MeHg) is a highly toxic contaminant in coastal environments and poses threats to marine fish in early life stages (ELSs). However, MeHg toxicity to fish embryos and larvae is not well investigated. This study investigated the antioxidant defenses and immune responses of flounder Paralichthys olivaceus larvae exposed to waterborne MeHg (0, 0.1, 1.0 and 10.0 µg L-1) for 35 days, from embryogenesis to settlement. The results revealed that metal accumulation in the larvae was positively correlated with MeHg concentration, reduced larval growth and survival. The activities of catalase and glutathione reductase were significantly increased at 10.0 µg L-1, while glutathione peroxidase activity and lipid peroxidation level were significantly increased at concentrations over 1.0 µg L-1. The corresponding antioxidant-related genes were upregulated under MeHg exposure (cat and gpx at 10.0 µg L-1; gr over 1.0 µg L-1). Lysozyme content was significantly increased, but immunoglobulin M content was significantly decreased at 10.0 µg L-1. The immune-related genes were significantly upregulated (hsp70 at 0.1 and 10.0 µg L-1; lzm and il-1ß over 1.0 µg L-1; tnf-α and il-6 at 10.0 µg L-1) or downregulated (igm, over 0.1 µg L-1). Overall, MeHg exposure induced oxidative stress and caused immunotoxicity at concentrations over 1.0 µg L-1 and 10.0 µg L-1, respectively. The transcription of selected genes correlated with the corresponding biochemical markers in response to MeHg toxicity. These findings improve our knowledge to better understand the mechanisms by which marine fish at ELSs cope with oxidative stress and immunotoxicity induced by MeHg.

Interactive effects of strontium and barium water concentration on otolith incorporation in juvenile flounder Paralichthys olivaceus.

Although the relationship between the incorporation of an element into otoliths and the concentration of the element in water has been extensively investigated in many fish species, the interactive effects of multiple elements in water on the otolith incorporation of an element are not adequately explored or well understood. In this study, 16 treatments in triplicate using strontium (Sr; 1, 2, 3 and 4 times the ambient baseline, 6.5 mg l-1) and barium (Ba; 1, 2, 4 and 6 times the ambient baseline, 40 µg l-1) as categorical variables in an orthogonal design were established to evaluate the relative or interactive effects of water elements on otolith elemental incorporation in juvenile flounder Paralichthys olivaceus (from 15 to 116 days post hatching). The results revealed that otolith incorporation (Me:CaOtolith) of Sr and Ba were positively dependent on the concentrations of the elements in water (Me:CaWater). Overall, Sr was incorporated into otoliths more efficiently than was Ba, and the partition efficiency (DMe) of both elements decreased with increasing water elemental concentrations. Increasing Sr concentrations in water appeared to negatively affect the uptake of Ba into otoliths rather than facilitate it, as previously reported in fish reared in freshwater and brackish water, or showed no effect on fish in seawater. Conversely, the Ba concentration in water did not influence the otolith uptake of Sr, which agrees with the findings for other fish species. When applying otolith microchemistry to fish ecology studies, it is essential to cautiously address the interactive effects of multiple elements in the environment on otolith elemental incorporation.

Toxicity Test Assay of Waterborne Methylmercury on the Japanese Flounder (Paralichthys olivaceus) at Embryonic-Larval Stages.

Methylmercury (MeHg) is a widespread pollutant in aquatic ecosystems, but its toxicity to the early life stages of marine fish has not been adequately investigated. This study used acute toxicity tests on embryonic-larval stages of a marine flounder Paralichthys olivaceus to determine the LC50 values for embryos and larvae and evaluate the responses of several biological endpoints to subacute MeHg exposure. Under exposures (0-15 µg L-1) below LC50 values ( < 15.3 µg L-1 for embryos and 16.3 µg L-1 for larvae), embryos were more sensitive to MeHg than were the larvae. MeHg exposures at ≥ 13 µg L-1 increased morphological deformities and mortality, reduced growth and yolk absorption rate of the embryonic-larval flounder. These endpoints were sensitive to MeHg and their responses were dose-dependent. They could be used as bioindicators for assessing MeHg toxicity to the ELS of the flounder. Embryonic-larval flounder could be a useful fish for ecotoxicological assessment of MeHg in marine ecosystems.

Trophic transfer, biomagnification and risk assessments of four common heavy metals in the food web of Laizhou Bay, the Bohai Sea.

This study investigated the trophic transfer of four common toxic metals (Cd, Cr, Cu and Hg) in the food web and assessed their potential ecological risks in Laizhou Bay, a spawning area for fishery populations in the Bohai Sea, North China. Based on the predation relations of 43 species that were representatives of the main trophic levels (TLs), a simplified food web was constructed using stomach content analysis and stable nitrogen isotope ratio (δ15N) analysis. Using copepods as the baseline species (TL = 2.00), the TLs of the organisms ranged from 1.96 (Polychaeta) to 4.47 (Japanese flounder) and showed the following ranking order: predatory pelagic or demersal fish > medium demersal fish > crustacean, cephalopod, small pelagic or demersal fish > zooplankton and Polychaeta. The metals showed different trophic transfer behaviors in the food web. Hg and Cr tended to be efficiently biomagnified between TLs, along the main food chains and in the food web. Cu biodiluted significantly with increasing TLs, while Cd showed no biomagnification or biodilution trends in the food web. At low or moderate levels of Cd and Hg, potential ecological risks were detected in the water and sediments at only a few sites, indicating their overall low ecological risks in the environment. The metals in the important fishery species (four top predatory fish, two cephalopods and eight crustaceans) were below the permissible limits, except for Cd in octopus and paddle crab, which reached or exceeded the most restrictive criteria. Based on the provisional tolerable weekly intake (PTWI) criteria, the safe weekly human consumption levels by humans of the predatory fish, cephalopods and crustaceans were species-specific (0.20-4.44 kg) and should be cautiously assessed.

Bioaccumulation of heavy metals and health risk assessment in three benthic bivalves along the coast of Laizhou Bay, China.

This study investigated the tissue- and species-specific bioaccumulation of heavy metals (Cr, Cu, Hg, Zn, As, Cd, and Pb) in three benthic bivalves (the ark shell, Scapharca subcrenata; the surf clam, Mactra veneriformis; and the Manila clam, Ruditapes philippinarum) collected from the coast of Laizhou Bay in the Bohai Sea. The results demonstrated that the visceral masses of the bivalves tended to accumulate heavy metals more efficiently than their muscles. The capacities of the bivalves to bioaccumulate metals followed a similar order: Cd>Hg>Zn=As>Cu>Cr=Pb. The conditions of metal contamination in the bivalves tended to be worse along the eastern coast than in other regions. Overall, the Manila clam was more severely contaminated by heavy metals than the surf clam and ark shell. Judging by the hazard quotients (HQ) of the metals in the muscles of the bivalves, the greatest hazard risk to human health comes primarily from As.

Morphological and histological changes in digestive tract development during starvation in the miiuy croaker.

A histological method was used to describe the ontogenetic development of the digestive tract of laboratory-reared miiuy croaker (Miichthys miiuy) and to evaluate the effects of short-term food deprivation on the morphology and histology of the digestive tract. Larvae and juveniles were maintained at 24 °C in a thermostatically controlled system. Three starvation experiments were conducted during different developmental stages: 1-7 days after hatching (dah; prior to benthic swimming); 26-35 dah (during settling); and 42-53 dah (after benthic swimming). According to the structural changes in the ontogenetic development of the digestive tract, three stages were observed. The first stage was from hatching to 3 dah; the digestive tract was undifferentiated in newly hatched larvae and then showed remarkable morphological changes and differentiation. During this period, larvae depended on endogenous nutrition. The second stage (4-20 dah) was a critical period in which larvae transitioned from endogenous feeding to exogenous feeding and the digestive tract fully differentiated into the buccopharynx, oesophagus, stomach, anterior intestine and posterior intestine. Goblet cells and vacuoles appeared in the digestive tract, and pharyngeal teeth and taste buds developed. During the third stage (20-36 dah), the gastric glands developed and the stomach differentiated into the fundic, cardiac and pyloric regions. At 25 dah, pyloric caeca developed and mucosal folds and spiral valves were clearly distinguishable. After 30 dah, the digestive tract did not undergo any noticeable differentiation, indicating the complete development of the digestive system. The wet weight and SGR (specific growth rate) of miiuy croaker larvae and juveniles greatly decreased when they were deprived of food, and compensatory growth was observed in re-feeding juveniles. The livers of starved larvae and juveniles were atrophied and dark coloured, the intestines were transparent and thin, and the stomach cubages were reduced. The histological effects of starvation were mainly evident in the degeneration of cells in digestive organs, as seen in the shrinkage and separation of cells and the loss of intercellular substances in the liver, pancreas, intestine and stomach. These changes became more severe with increased duration of starvation. In addition, the histological structure of the digestive tracts of starved larvae and juveniles partly recovered after re-feeding, and the effects of starvation on miiuy croaker were age dependent.

Tissue-specific accumulation of cadmium and its effects on antioxidative responses in Japanese flounder juveniles.

This study investigated the accumulation of cadmium (0-8 mg Cd L⁻¹) and its toxicological effects on oxidative stress biomarkers in different tissues of Japanese flounder juveniles. Following Cd exposure for 28 d, accumulation of Cd in fish was dose-dependent and tissue-specific, with the greatest accumulation in the liver, followed by the kidney, gill, and muscle. Although the gill and liver mounted active antioxidant responses at ≥ 4 mg L⁻¹ Cd including a decrease in glutathione level and GST and GPx activities, the antioxidant response failed to prevent lipid peroxidation induction in these organs. In the kidney, increased GPx and GST activities and decreased SOD activity were observed in fish exposed to high Cd concentrations, but LPO levels did not significantly differ among the exposure concentrations. The gill was most sensitive to oxidative damage, followed by the liver; the kidney was the least affected tissue.

Toxicity testing of waterborne mercury with red sea bream (Pagrus major) embryos and larvae.

Acute toxicity tests revealed that, in red sea bream (Pagrus major) embryos, 24 and 48 h LC(50) values of waterborne HgCl(2) were 67.3 and 39.1 µg Hg(2+) L(-1). In larvae, 48, 72 and 96 h LC(50) values were 41.9, 36.1 and 34.8 µg Hg(2+) L(-1), respectively. Sub-chronic toxicity tests indicated that mercury concentrations ≥20 µg Hg(2+) L(-1) decreased hatching success, increased mortality and induced teratogenicity in embryos and larvae. The NOEC, LOEC and MATC values were 8.0, 16.3 and 11.4 µg Hg(2+) L(-1) for hatching success, mortality and teratogenicity; while those were 27.0, 36.9 and 31.6 µg Hg(2+) L(-1) for body length and specific growth rate, respectively.

Short-term mercury exposure affecting the development and antioxidant biomarkers of Japanese flounder embryos and larvae.

This study investigated the acute and sub-lethal toxicities of waterborne mercuric chloride to Japanese flounder (Paralichthys olivaceus) embryos and larvae. Acute toxicity tests indicated that the 48-h LC(50) values of mercury to the embryos and larvae were 48.1 (32.8-63.6) and 99.4 (72.9-147.0) µg L(-1), respectively. Mercury could cause low hatching success, delayed hatching process, reduced growth at concentrations ≥20 µg L(-1), and induce reduced survival and higher morphological malformations at concentrations ≥40 µg L(-1) in the embryos and larvae. In sub-lethal toxicity test, superoxide dismutase (SOD) and catalase (CAT) activities, reduced glutathione (GSH) and malondialdehyde (MDA) contents of the larvae were significantly increased, while glutathione-S-transferase (GST) was decreased by 10 days of 0-10 µg Hg(2+)L(-1) exposure. These findings suggested that the hatching, survival, growth and antioxidant biomarkers of the flounder were sensitive to the highest mercury concentrations and could thereby serve as potential biomarkers for evaluating mercury contamination in the aquatic environment.

Toxicity of short-term copper exposure to early life stages of red sea bream, Pagrus major.

Acute (0, 0.1, 0.2, 0.4, 0.8, 1.6 mg Cu/L) and chronic (0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12 mg Cu/L) toxicity tests of Cu with embryonic and larval red sea bream, Pagrus major, were carried out to investigate their biological responses to Cu exposure in static water at 18 +/- 1 degrees C (dissolved organic carbon, 1.8 +/- 0.65 mg C/L; hardness, 6,183 +/- 360 mg CaCO3/L; salinity, 33 +/- 1 per thousand). The 24- and 48-h LC50 (median lethal concentration) values of Cu for embryos were 0.23 and 0.15 mg/L, whereas the 48-, 72-, and 96-h LC50 values for larvae were 0.52, 0.19, and 0.13 mg/L, respectively, suggesting that embryos were more sensitive to Cu toxicity than larvae. Copper exposures at > or =0.06 mg concentrations caused low hatching success, a delay in the time to hatching of embryos, and reductions in the growth and yolk absorption of the larvae, whereas high mortality and morphological malformations occurred in the embryos and larvae at > or =0.08 mg/L concentrations. Copper concentration did not significantly affect the heart rate of the embryos, but it significantly decreased the heart rate of the newly hatched larvae when the Cu concentration was > or =0.08 mg/L, suggesting that Cu at high concentrations could induce heartbeat disturbances in red sea bream more easily at the larval stage than at the embryonic stage. Hatching success, time to hatching, growth rate, morphological abnormality, yolk absorption, and heart rate were Cu concentration-dependent and could be effective endpoints for evaluating Cu toxicity to the early life stages of red sea bream in nature.