The Atlanto-Mediterranean holothurian Holothuria tubulosa is among the conspicuous benthic invertebrates in the shallow sublittoral zone. It is an edible species, harvested at the Aegean Sea and utilized as fishing bait. Considering the lack of information for the Aegean populations, a one-year survey, based on monthly or semimonthly samples, was carried out focusing on population structure, allometric relationships and reproductive status of H. tubulosa stocks in Pagasitikos Gulf. Population density varied around 9.93 individuals/100 m². This value was rather low compared with other studied Mediterranean populations of the species, possibly due to the scarcity of seagrass meadows in the area studied. All measured biometric characters showed high plasticity, and all the examined morphometric relationships followed negative allometry indicating a change to the shape of the animal's body as it grows. Holothurians’ length was a moderate predictor of biomass since r values reached 60%; in contrast a very strong relation was observed between drained and gutted weight. Size–frequency distribution analysis was unimodal with the exception of spring where a second mode of larger sized individuals appeared. The gonadosomatic index showed a single spawning season per year, in late summer; accordingly the reproductive cycle of the species showed a clear annual pattern which was highly correlated with the seasonal variations of temperature.

The spatial and seasonal impact of fish farming on the water column of two fish farms in the Eastern Mediterranean was investigated, between July 2004 and April 2005. In the area of each fish farm, three stations were sampled. One was located at the centre of the fish farm, the other at a distance of 50 m from the centre and the last one at a distance of 300 m from the fish farm centre. At each sampling station, water samples were collected at the surface, at 5 m and at every further 10-m depth from the surface to the bottom, for nutrient analysis (ammonium, nitrite, nitrate, phosphate, silicate). Statistical analysis showed significant differences between seasons for all nutrients, with the exception of nitrite in one of the farms. Furthermore, ammonium, nitrite, phosphate and silicate values showed significant differences among sampling stations. The maximum concentrations of the above nutrients (1.64, 0.10, 2.57, 0.28 and 4.89 μM respectively) were recorded at the sampling stations located at the centre of each fish farm and they were gradually reduced with increasing distance from the cages. The concentrations of nutrients did not appear to exceed permitted levels for the appearance of eutrophication. The maximum concentrations were considerably lower than those observed previously in the study area.

The accumulation of copper and zinc, the basic components of anti-fouling paints, was examined in cultured sea bass Dicentrarchus labrax and sea bream Sparus aurata. Samplings were carried out at 4 eastern Mediterranean fish farms. Two of the farms used nets treated with anti-fouling paints, and 2 used untreated nets. At each farm samples of sediment and fish tissue (muscle, liver and gills) were analysed for heavy metal concentrations. The results showed that while total copper and zinc concentrations in sediments were quite similar in samples collected from the 4 farms, the extractable copper concentration in sediment from farms using anti-fouling treatment was 2 to 3 times higher than from those using untreated nets. Statistical analysis revealed no significant differences for either metal between sediment samples from farms using anti-fouling treatment and those which did not, except for extractable copper concentrations. However, analysis of the biological samples showed that copper concentrations in muscle tissue were lower in samples from farms using untreated nets, with the highest copper concentrations being observed in fish livers from farms using anti-fouling paints. General linear model results indicated significant differences between heavy metal concentrations in fish samples from farms using antifouling paints and those which did not. Furthermore, 1-way ANOVA indicated that these differences were confined to liver tissue for zinc, whereas significant differences for copper were seen in all tissues (except for gills of sea bream) for both species studied. These results indicate that the use of anti-fouling paints may be a potential source of metal accumulation in cultured fish

Spatial and temporal effects of fish farming on the benthic community structure at 2 fish farms in the Eastern Mediterranean were investigated between July 2004 and April 2005. In the area of each fish farm, 3 stations were sampled. At each station, sediment samples were collected for analysis of organic carbon, organic matter and benthic community parameters. There were statistically significant differences in organic matter and organic carbon among all stations. This impact seems to be only spatial, since 1-way ANOVA indicated no significant differences in organic matter and organic carbon between seasons for both farms. Furthermore, significant differences were found in species number, abundance and species richness among stations and seasons for one of the farms (2-way ANOVA). One-way ANOVA indicated that the significant differences, detected in the benthic community parameters of this farm, were spatio-temporal for species number, temporal for abundance and spatial for species richness. The spatial effect of fish farming on benthic community structure was present up to 50 m from the centre of cages on one farm and between 50 and 300 m from the other farm. Capitella capitata was the most dominant species at the farm sites, while Nephthys hystricis was the most dominant species at the control sites. In all cases, the benthic assemblages in the immediate vicinity showed symptoms of disturbance, but the spatial and temporal extent of this effect was less than one would expect considering the fact that the study area is located in a semi-enclosed gulf

Although aquaculture is considered the fastest growing food production industry, nevertheless there is little information regarding pollutant levels in cultured fish. Samples of cultured sea bass – Dicentrarchus labrax (Linnaeus, 1758), sea bream – Sparus aurata (Linnaeus, 1758), and sharpsnout sea bream – Diplodus puntazzo (Walbaum, 1792) from three fish farms located in the Eastern Mediterranean which utilized antifouling paints on the nets were analyzed for quantitative determination of zinc (Zn), chrome (Cr), and copper (Cu) in the gills, the liver, and the muscle separately for each tissue and fish. The results show that the highest levels of zinc (up to 29.6 mg kg⁻¹ dry wt) were found in the gills of all samples of sea bream and sharpsnout sea bream while in the samples of sea bass, the highest levels of zinc and chrome were found in the liver (up to 39.3 and 13.8 mg kg⁻¹ dry wt, respectively). Insofar, as copper is concerned the highest exposure was found in the liver of sharpsnout sea bream (up to 5.49 mg kg⁻¹ dry wt). The results indicate that the use of antifouling paints in aquaculture practices are a significant source of chemical pollution in cultured fish and poses a risk to the exposed organisms.