Concentrations of zinc,manganese, copper,cadmium, magnesium and iron in ten species of algae and sea water from Aqaba,Jordan

Concentrations of zinc, manganese, copper, cadmium, magnesium and iron in three species of red, four species of brown and three species of green macroalgae, and also in sea water have been determined at two localities along the coast of Aqaba. Significant differences in metal concentrations were found between the various species (P<0·01). Similar significant differences were found with regard to different metals (P<0·001). Concentration factors ranged between 10² for Cd and 9·2 × 10⁴ for Fe. The difference in levels of metals between the two localities, however, was not significant (P > 0·05). Of the three groups of algae examined, rhodopytes exhibited the highest concentration power of metals.     

Mercury pollution in sediments,benthic organisms and inshore fishes of Haifa Bay,Israel

Total mercury concentrations were determined in surficial sediments, eleven species of benthic organisms and six species of fish from Haifa Bay, Israel. The results show that essentially all of the shallow water zone of the Bay receives anthropogenic mercury. A mercury-cell chlor-alkali plant was identified as the source of pollution. Surficial sediments in the vicinity of the plant, containing up to 0·99 μg Hg/g dry weight, were up to 157 times enriched in mercury relative to an unpolluted area. Mercury levels in the benthic organisms reflected the levels in the sediments. Maximal concentrations reaching 38·7 and 18·2 μg Hg/g dry weight were found in the carnivorous gastropod molluscs Arcularia circumcinta and Arcularia gibbosula, respectively. In all fish species, specimens caught in Haifa Bay had higher mercury concentrations in the muscle tissue than specimens caught south of the Bay. A maximal value of 1·66 μg Hg/g wet weight was recorded in Diplodus sargus.     

A comparison of ozone and chlorine toxicity to three life stages of the American oyster Crassostrea virginica

The effects of ozone-produced oxidants (OPO) on three developmental stages of the American oyster, Crassostrea virginica, were evaluated. Both straight-hinge (48-h post fertilisation) and setting pediveliger larvae were exposed to a series of OPO concentrations ranging from 0·05 to 0·30 mg/litre OPO (as total residual chlorine) at 25°C for 96 h. Mortality was used as the response parameter and results were quantitatively compared with the effects of chlorine-produced oxidants (CPO) obtained from the literature on these same developmental stages. Adult oysters (2- to 4-year class) were exposed to OPO concentrations ranging from 0·01 to 0·50 mg/litre at 15°C for 5 days and to the same concentration range at 25°C for two consecutive 6-day periods. Shell deposition and faecal matter accumulation were used as the response parameters for this stage.Straight-hinge larvae were significantly more sensitive to OPO than setting pediveliger larvae. Both larval stages were significantly more sensitive to CPO than to OPO. Shell deposition was significantly inhibited at all OPO concentrations for both 15°C and 25°C acclimated adult oysters. No significant differences were found between the shell deposition response of oysters at the two acclimation temperatures. Faecal matter accumulation was significantly reduced at OPO concentrations ≥ 0·05 mg/litre at both 15°C and 25°C. It was significantly (p < 0·05) greater for 25°C acclimated oysters than for 15°C acclimated oysters at OPO concentrations < 0·10 mg/litre but not at higher concentrations.     

Behavioural responses of selected marine fishes to chlorinated seawater

Behavioural responses to chlorinated seawater were studied in the laboratory using eight species of fish (topsmelt, Atherinops affinis [Ayres]; pile perch, Rhacochilus vacca [Girard]; señorita, Oxyjulis californica [Günther]; blacksmith, Chromis punctipinnis [Cooper]; northern anchovy, Engraulis mordax [Girard]; opaleye, Girella nigricans [Ayres]; bluebanded goby, Lythrypnus dalli [Gilbert] and mussel blenny, Hypsoblennius jenkinsi Jordan and Evermann) which occur near the Units 7 and 8 discharge of Southern California Edison's Redondo Beach Steam Generating Plant in King Harbor, California, USA. All species except Engraulis demonstrated prolonged avoidance of chlorinated quadrants of the behaviour chamber. The avoidance thresholds were species-specific and species totally avoided estimated total residual oxidant (TRO) concentrations from 0·094 to 0·456 mg/litre. Calculated significant avoidance thresholds averaged 0·066 mg/litre TRO; young Atherinops significantly avoided TRO concentrations as low as 0·028 mg/litre (p < 0·001). The highest avoidance thresholds were exhibited by sedentary species and were modified by the presence of cover inside the behaviour chamber. The avoidance response protected against mortality in all species except Lythrypnus and Engraulis.     

Effects of dechlorinated seawater on fish behavior

Behavioral responses to chemically dechlorinated seawater were studied using two species of marine fish associated with power plant discharge areas off Southern California. Opaleye (Girella nigricans) neither avoided nor were attracted to chlorinated seawater containing 0·1 mg/liter total residual oxidants (TRO) which had been dechlorinated using equimolar or excess sodium thiosulfate. Blue-banded goby (Lythrypnus dalli) did not avoid dechlorinated seawater initially containing 0·1 or 0·9–1·0 mg/liter TRO. Previously it has been shown that opaleye avoided chlorinated seawater with oxidant concentrations of 0·1 mg/liter and blue-banded gobies avoided 0·9–1·0 mg/liter TRO. Elimination of chlorine-produced oxidants by thiosulphate dechlorination resulted in 100% survival in both species. The toxicological implications of exposure to dechlorinated seawater are discussed.     

Seasonal fluctuations and compositions of two populations of small demersal fishes on the west coast of Scotland

The soft sediment fish communities below 20 m depth were studied at two sites on the west coast of Scotland (Irvine Bay, Firth of Clyde and the Lynn of Lorne) using small meshed beam trawls. In both cases the emphasis was on the small demersal fish (<15 cm) within these communities. The Irvine Bay community was studied between May 1978 and December 1979 and the Lynn of Lorne community between February 1975 and October 1976.Twenty-seven fish species were recorded in Irvine Bay and 32 in the Lynn of Lorne. In both communities four species constituted more than 78% of the total annual abundance, two gobies (Lesueurigobius friesii and Pomatoschistus norvegicus) were high in the dominance ranking for both sites. The species abundance lists were similar for both sites (0·62 level of similarity) but the species lists for each site were different (0·36 level of similarity). The overall mean density of small demersal fish was similar for both sites (Irvine Bay = 0·045 individuals m^?2 and the Lynn of Lorne = 0·047 individuals m^?2). There were two periods of high abundance for both communities (late autumn to winter and late spring). There was, however, a low repeatability between successive years. The species richness (D) was relatively high (Irvine Bay = 1·5-3·08, Lynn of Lorne = 1·4-3·34) as was the species diversity (H′) (Irvine Bay = 1·17-1·97, Lynn of Lorne = 1·23-1·95). The proportional representation ($\text{J′}$) of each species within the community was greater in Irvine Bay ($\text{J′}$ = 0·57-0·77) than in the Lynn of Lorne ($\text{J′}$ = 0·50-0·72). Therefore these two communities of small demersal fish appeared to be similar at the community level but the way in which this was achieved was different.     

Hepatic lesions in English sole (Parophrys vetulus) from Commencement Bay,Washington (USA)

Prevalences of idiopathic hepatic lesions in English sole (Parophrys vetulus) were evaluated at 15 transects in Commencement Bay, Washington (a chemically contaminated embayment), and at two transects in Carr Inlet. Washington (a relatively uncontaminated reference embayment). The lesions considered were neoplasms (tumors), foci of cellular alteration (putative preneoplasms), megalocytic hepatosis and nuclear pleomorphism.Prevalences of one or more of the four lesions at 10 (67%) of the Commencement Bay transects were significantly higher (P ≤ 0·05) than the prevalence observed in Carr Inlet. Prevalences of neoplasms and foci of cellular alteration were correlated positively (P ≤ 0·05) with fish age, but none of the four lesions exhibited a relationship with fish sex. A significant concordance (P ≤ 0·005) was found among the spatial distributions of the four lesions, suggesting that all were induced by similar stimuli. Length-at-age did not differ significantly (P > 0·05) between fish with and without hepatic lesions, indicating that fish growth did not appear to be influenced by the presence of the lesions. The spatial patterns of lesion prevalences observed in this study were similar to those found at similar locations in a precious study 3–5 years earlier, suggesting that these patterns are persistent.     

饲料维生素C对花鲈(Lateolabrax japonicus)幼鱼生长和免疫的影响

采用单因子实验设计方法,进行了饲料中添加维生素C对花鲈幼鱼生长（增重率、存活率、特定生长率、饲料效率）、免疫反应（血清中溶菌酶活性和血清总补体活性）和组织中维生素C积累量影响的研究。结果表明,随着饲料中维生素C添加量由0提高到98．9mg／kg,花鲈的增重率和特定生长率显著提高。以特定生长率为指标,花鲈最佳生长性能的饲料维生素C添加量为103.0mg／kg左右;饲料中维生素C添加量在0-98．9mg／kg时,花鲈幼鱼肌肉和肝脏中维生素C的积累量随饲料中维生素C的增加而显著增加（P〈0．05）,花鲈幼鱼获得最大肝脏和肌肉中维生素C的积累量时,饲料中维生素C最低添加量为97．2mg／kg和105.0mg／kg;花鲈幼鱼血清溶菌酶和总补体活性随着维生素C添加量的增加而显著升高,维生素C添加量达到396．4mg／kg时,血清溶菌酶和总补体活性较高。综上所述,花鲈生长和免疫的维生素C适宜添加量为400mg／kg左右。     

Bioaccumulation and trophic transfer of mercury in striped bass (Morone saxatilis) and tautog (Tautoga onitis) from the Narragansett Bay (Rhode Island,USA)

We examined the bioaccumulation and trophic transfer of mercury in two marine finfish species, striped bass (Morone saxatilis) and tautog (Tautoga onitis), collected from the Narragansett Bay (Rhode Island, USA). For each of these target fish, white muscle tissue was analyzed for total mercury (Hg) and results were evaluated relative to fish age, body size, and Hg content of preferred prey. Dietary and stable isotope analysis was also used to elucidate the effect of trophic processes on Hg concentrations in fish. The Hg content of muscle tissue was positively correlated with fish age and length for both species, although striped bass accumulated Hg faster than tautog. Accelerated Hg bioaccumulation in striped bass is consistent with its high trophic level (trophic level = 4.07) and Hg-enriched prey (forage fish and macrocrustaceans; mean Hg content = 0.03 mg Hg kg wet wt^?1). In contrast, tautog maintain a lower trophic status (trophic level = 3.51) and consume prey with lower Hg levels (mussels and crabs; mean Hg content = 0.02 mg Hg kg wet wt^?1). Despite differences in Hg bioaccumulation between target fish, the mean Hg concentration of tautog exceeded levels in striped bass (0.24 and 0.16 mg Hg kg wet wt^?1, respectively) due to a disparity in age-at-catch between sampled groups (mean age of tautog and bass = 11.3 and 4.3 yr, respectively). Taking into account legal minimum catch lengths further revealed that 75.0% of legal-size striped bass (>70.2 cm TL; n = 4) and 44.8% of tautog (>40.6 cm TL; n = 29) had Hg levels beyond the US EPA regulatory threshold of 0.3 mg Hg kg wet wt^?1. Moreover, Hg-length relationships suggest that each target fish meets this threshold near their minimum legal catch length. Our findings reiterate the value of species ecology to improve predictions of fish Hg and permit better management of human contamination by this important dietary source.     

Trace metals in the common porpoise, Phocoena phocoena

Mercury, cadmium, copper and zinc concentrations in brain, liver, kidney, heart and spleen of twenty-six specimens of the common porpoise (Phocoena phocoena) are presented. Mercury and cadmium levels in liver and kidneys tended to increase with length of animal, but copper and zinc levels show no such trends. The proportion of methylmercury to total mercury (9%–57%) in the liver decreased with increasing total mercury concentrations. Lead, chromium, nickel and cobalt levels were below the analytical detection limits (0·5, 1·0, 1·0 and 2·5 μg^?1, respectively).     

Study of metal contents of elasmobranch fishes: part 1—metal concentration in the muscle tissues of a dogfish, squalus mitsukurii

Concentrations of Hg, Zn, Fe, Cd and Cu in the muscle tissues of a dogfish, Squalus mitsukurii, were determined by atomic absorption spectrometry and found to be in the ranges of f0·019–2·13, 1·8–3·6, 1·5–5·7, 0·001–0·018 and 0·12–0·70 μg/g wet weight, respectively. The frequency distributions of concentrations, with the exception of mercury, were found to be log-normal. The correlation coefficient between mercury content and total length was positive and large and statistically highly significant. For other metals negative correlations were observed. Mercury concentration in the muscle was found to increase in proportion to the total length cubed. Regression of mercury concentration on age of sharks was shown to be linear. Analysis of covariance showed that the difference between sexes was not statistically significant, either in slope or in height. The concentration of mercury in the muscle tissues of embryos was considerably lower, Cd roughly the same and Zn and Fe higher than those of mothers. The concentrations of Zn, Fe and Cu are higher in the embryonic stage and immediately after birth than in later stages of growth.     

Decreased fitness of cod (Gadus morrhua L.) from polluted waters

The rotatory-flow technique was applied to cod, Gadus morrhua L., from different regions of Scandinavia. Fish from three area (Vikanes, Norway and Kristineberg and Gårdby, Sweden) in which the water is relatively unpolluted did not differ significantly as to the mean reaction quotient. Experiments to determine the fitness of cod from the Kristineberg and Stenungsund areas were conducted during a 29-month period. The mean reaction quotients for Stenungsund cod were significantly lower than those for Kristineberg cod for all the experiments except for the final tests conducted during November, 1975. They did not vary inversely to the amounts of monomethyl mercury, PCB and DDT analysed in the trunk muscles of tested specimens.In order to determine the effect of these toxic compounds on the efficiency of the fish from Kristineberg, cod were treated with sublethal doses given by oral intubation. A significant decrease in the reaction quotients was obtained with the lowest level of DDT used (1 ppm), the decreases in the reaction quotients being linearly correlated (r = 0·60) with the amount of DDT in the muscle tissue (mean value 0·36 ppm wet tissue). For PCB and mercury the corresponding mean levels in muscles were 1·8 and 1·5 ppm, respectively. These amounts are about 10, 30 and 75 times greater, respectively, than those found in the Stenungsund cod. It is, however, doubtful whether the distribution of the toxicants within the fish body corresponded to that occurring in the sea.     

Phenolics in aquatic ecosystems: A selected review of recent literature

This review surveys the pertinent literature on phenolics in the aquatic ecosystem. Approximately 2% of the total organics manufactured in the US were phenols. Of the total phenolics produced in the US, 96% were synthetic and 4% were naturally occurring. Synthetic phenols arise from coking of coal, gas works and oil refineries, chemical plants, pesticide plants, wood preserving plants and dye manufacturing plants. Natural phenolics occur from aquatic and terrestrial vegetation and much of this is released by the pulp and paper industry.Toxicity of phenolics has been studied on selected microbes (e.g. protozoa, yeast and bacteria), algae, duckweed, and numerous invertebrates and vertebrates. Depending on the organism tested, the acute toxicity of phenol varies from 6·5 to 1840 mg/litre phenol. For other phenolics toxicity ranges from 0·084 to 555 mg/litre. The toxicity of phenolics varies with the type, position and number of substitutions on the parent molecule. Environmental factors affect the toxicity of phenolics and these include photolytic action, microbial degradation, pH, water hardness and temperature. Based on limited data, toxicity of phenolics may be less in continuous flow tests than in their sensitivity to phenolics as does the presence of oxygen. A seasonal factor may also affect the sensitivity of various fish. Starvation and lack of suitable substrate for bottom fauna increases organism sensitivity to phenol. The source of test animals may affect their sensitivity to phenolics and this effect may be due to short-term physiological acclimation and genetic selection.Studies on the biological effects of phenolics are limited and varied. Fish development and embryo survival were not affected by phenol levels less than 25 mg/litre. Amphibian embryos were sensitive to 0·5 mg/litre phenol. Pentachlorophenols inhibited fish growth at levels down to 1·74, μg/litre.Exposure of fish to phenol in concentrations as low as 4 mg/litre caused haemorrhaging at the base of the fins. Two hour exposure to 6·5 mg/litre phenol caused disruption of blood vessel walls and gill epithelium. Oedema and blood infiltration was a common effect observed in most major tissues studied from fishes exposed to phenol. Phenol, at 12·5 mg/litre, reduces the levels of neurohormones in fish exposed for 10 days. The effects of pentachlorophenol on blood glucose and blood lactate levels, and in vivo and in vitro activity levels of seven liver enzymes of eels are discussed. Pentachlorophenol, at 1·8 μg/litre, decreased assimilation conversion efficiency in underyearling salmon. Phenol also affects immunoglobin levels, blood protein levels and tissue micro-element levels. Feeding rates are affected by phenolics. Phenolics affect oxygen consumption rates and the effect may be on uncoupling of oxidative phosphorylation with a subsequent reduction of ATP formation.Many aspects of behaviour are affected by phenolics and the phases of ‘intoxication’ leading to death have been described for fish and invertebrates.Fish detoxify phenolics by forming conjugate glucuronides and sulphates. Body burdens of phenolics varied with exposure time and exposure concentration. When fish pre-exposed to phenol are transferred to clean water, body burdens drop up to 90% after three to four hours. Depuration rates for other phenolics took longer; up to 30 days for pentachlorophenol.Little research has been done on the cycling of phenol and phenolics (other than pesticides) in aquatic ecosystems. Microbial degradation will decompose phenolics rapidly if suitable bacteria are present. Other factors affecting the loss of phenolics from aquatic ecosystems include photolysis, adsorption and dilution. Phenol entering subterranean aquifers may not dilute or degrade very quickly. In one documented case well-water levels up to 200 mg/litre were measured 18 months after a spill.     

不同铁水平饲养对大菱鲆(Scophthalmus maximus)生长及耐低氧能力影响的研究

铁元素作为细胞色素的重要成分参与鱼类细胞内的氧化还原供能过程,在鱼类应对低氧胁迫时发挥重要作用。以硫酸亚铁为铁源,研究不同铁水平饲养对大菱鲆(Scophthalmus maximus)生长及耐低氧能力的影响。在含铁量为463 mg/kg的基础饲料中添加0(A组)、75(B组)、150(C组)、225(D组)和300(E组)mg/kg铁离子,探究不同铁水平饲喂对大菱鲆常氧下的生长、血清生理生化指标以及抗低氧胁迫的影响。结果显示,常氧情况下,随着饲料中铁含量的增加,上述指标呈先增加后下降的趋势(P<0.05),且C、D组均为峰值显著高于A、B、E三组(P<0.05)。低氧胁迫及耐受实验结果显示,随着低氧胁迫的加剧,C、D两组抗氧化酶活性(SOD,GSH-PX)、低氧[DO=(2.0±0.5) mg/L]死亡率均显著高于或低于其他三组(P<0.05)。铁作为重要的氧载体和电子传递体影响着生物体的物质代谢和能量代谢。研究表明饲料铁水平613~688mg/kg的饲养对大菱鲆生长性能、抗氧化系统的增强和提高低氧耐受能力具有促进作用,研究结果可为鱼类健康养殖和功能性饵料研制提供新数据支撑。     

饲料维生素C对美国红鱼(Sciaenops ocellatus)生长、免疫的影响

采用单因子实验设计方法, 进行了饲料中添加维生素C对美国红鱼生长(平均增重率、存活率、特定生长率、饲料效率)和免疫反应[血清中溶菌酶活性、血清总补体活性和超氧化物岐化酶(SOD)活性]影响的研究。结果表明: 随着饲料中维生素C添加水平由0提高到100mg/kg时, 美国红鱼的增重率和特定生长率显著提高。以特定生长率为指标, 美国红鱼最佳生长性能的饲料维生素C添加量为104.5mg/kg左右; 饲料中维生素C水平在0—98.9mg/kg时, 美国红鱼肌肉和肝脏中维生素C的积累量随饲料中维生素C的增加而显著增加(P<0.05); 美国红鱼获得最大肝脏和肌肉中维生素C的积累量时饲料中维生素C最低添加量为128.1和104.0mg/kg; 美国红鱼血清溶菌酶和血清总补体活性在维生素C添加水平分别为98.9和198.7mg/kg时达到最高值, 随后变化不明显; 美国红鱼血清SOD活性随维生素C添加水平的增加而显著升高, 并且活性在198.7mg/kg达到最高值, 随后显著下降。综上所述, 美国红鱼维生素C生长和免疫的维生素C适宜添加水平为200mg/kg左右。     

Cadmium toxicity to three species of estuarine invertebrates

Three species of estuarine invertebrates, Palaemonetes pugio (grass shrimp), Pagurus longicarpus (hermit crab) and Argopecten irradians (bay scallop), were exposed to Cd in flowing seawater at concentrations of 0·06, 0·12, 0·25, 0·5 and 1·0 mg/litre. Incipient LC₅₀ values of 0·53 and 0·07 mg/litre were estimated for bay scallop and hermit crab, respectively. The toxicity curve for grass shrimp had not stabilised, but the incipient LC₅₀ value was estimated to fall within a range of 0·2 to 0·3 mg/litre. Short-term response, as measured by time to 50% mortality at the highest Cd concentration, was 10, 21 and 23 days for the bay scallop, hermit crab and grass shrimp, respectively. Scallop growth was inhibited at all exposure concentrations with a measured 42-day EC₅₀ value of 0·078 mg/litre Cd. Byssal thread detachment precedes death in bay scallops. An EC₅₀ value of 0·54 mg/litre Cd for byssal detachment was measured on day 8 of the bioassay before appreciable mortality. This compared favourably with the incipient LC₅₀ value of 0·53 mg/litre Cd. Cadmium accumulation occurred at all concentrations in bay scallop and grass shrimp.     

Differences in the effects of mercury on predator avoidance in two populations of the grass shrimp Palaemonetes pugio

Adult Palaemonetes pugio were collected from two tidal creek systems, Piles Creek (PC), a mercury polluted estuary, and Big Sheepshead Creek (BSC), a relatively pristine creek. Adult killifish (Fundulus heteroclitus), a natural predator of P. pugio, were obtained from BSC. For each test, ten treated (0·01 mg/liter mercuric chloride (HgCl), or 0·01 mg/liter methylmercuric chloride (MeHg)), or control shrimp here introduced into a tank containing three fish. The time between capture of the first and second BSC HgCl treated shrimp was significantly faster (P < 0·05), as was the time between the first and second capture (P < 0·05) of MeHg treated BSC shrimp when compared with their respective controls. In addition, significantly more (P < 0·025) BSC HgCl treated shrimp were captured after 120 min. No significant difference existed between control and HgCl treated PC shrimp; however, significantly more PC MeHg treated shrimp were captured after 60 (P < 0·05) min when compared with their respective controls. These data suggest that PC shrimp, subjected to mercury in their natural environment, are more tolerant to the sublethal effects of both HgCl and MeHg. These data also suggest that behavioral studies can be very sensitive assays for determining the effects of sublethal concentrations of toxicants on populations of organisms.     

Reduced survival and condition of the bivalves Protothaca staminea and Mytilus edulis buried by decomposing bark

The bivalves Protothaca staminea and Mytilus edulis were exposed to five depths of decomposing bark from an active log transfer facility for 13–96 days in a field experiment at Auke Bay, Alaska. Survival and condition of both species was inversely related to depth and duration of bark coverage. As little as 6 cm of bark reduced survival; survival declined most rapidly between 10 and 15 cm of bark. The depths of bark under which half the animals died after 96 days of exposure were 12·8 ± 1·6 cm for P. staminea and 10·9 ± 1·5 cm for M. edulis. Interstitial water in the bark deposits had low concentrations of dissolved O₂ (2·5–5·3 mg/liter) and elevated concentrations of hydrogen sulfide (1·0–8·1 mg/liter total sulfide) and ammonia (46–131 μg-at N/liter) compared to the surface water from the control treatment. Survival of P. staminea and M. edulis was inversely related to concentrations of hydrogen sulfide and ammonia and directly related to dissolved O₂ concentrations.     

Wind-related resuspension of sediments in the Peel-Harvey Estuarine System

Resuspension of bottom sediments accounted for 69–92% of mean deposition rates (11·6–69·3 gm^?2 day^?1) measured at 5 sites in the Peel-Harvey Estuarine System, Western Australia. Deposition rates at all but one of the sites were found to be correlated (P<0·05) with a function of wind combining a fetch factor with the number of hours of winds greater than 5 ms^?1 weighted by the third power of wind velocity. The exception was the only site with a cover of benthic algae (Cladophora) during the study. Wind-related resuspension greatly affects the forms and amounts of productivity in this system.     

Lifespan mercury accumulation pattern in Liza aurata: Evidence from two southern European estuaries

Mercury accumulation throughout the lifespan of Liza aurata (Risso, 1810) was analysed in four tissues (muscle, gills, liver and brain) in two southern European coastal ecosystems with distinct mercury contamination. Specimens from four to five age classes were captured in two sampling sites in the Ria de Aveiro (Laranjo bay and Mira), a system historically contaminated by industrial mercury, and in one site in the Mondego estuary, assumed as a mercury-free ecosystem. Mercury concentration in all tissues was found to be significantly higher in the Ria de Aveiro (Laranjo bay) compared to the Mondego, in accordance with the environmental contamination (water, sediments and suspended particulate matter). Significant differences inside the Ria de Aveiro (between the Mira and Laranjo bay) were only detected in the liver. This tissue registered the highest levels of mercury (ranging from 0.11 to 4.2 μg g⁻¹) in all sampling sites, followed by muscle, brain, and gills. In all sampling sites and tissues was denoted a mercury dilution pattern along the lifecycle (except in liver at the Mondego, the reference area where the concentrations are always very low). An exponential trend was found in the metal age variation patterns in Laranjo (the most contaminated area) and a linear trend in the Mira and the Mondego (the least contaminated areas). Organic mercury concentration in muscle generally accounted for over 95% of total mercury concentration, and followed the same accumulation pattern of total mercury. This fish species is of lesser importance in mercury transfer to adjacent coastal areas and although the consumption of fish from Laranjo may present some risk for the humans, this risk decreases with fish age/size.