Dietary ascorbic acid and alpha-tocopherol mitigates oxidative stress induced by copper in the thornfish Terapon jarbua

The protective effects of vitamins C and E against oxidative stress were evaluated in various tissues of thornfish Terapon jarbua exposed to copper. Preliminary bioassay tests performed with copper and T. jarbua revealed that 4.0, 2.5 and 1.0 mg L(-1) of copper were lethal (LC(100)), medial lethal (LC(50)) and sublethal (LC(0)) respectively. Oxidative stress parameters viz. lipid peroxidation, superoxide dismutase, catalase, glutathione peroxidase, and glutathione were evaluated in control and experimental fishes. Lipid peroxidation activity increased in tissues of copper exposed fishes, while the antioxidant system exhibited a reduction in their activity. On the contrary copper stressed fishes fed with vitamins C and E enriched pellet feed showed significant reduction in lipid peroxidation activity and the antioxidant levels increased reaching near normal levels comparable to control values. Bioaccumulation of copper was studied in addition to oxidative stress. Substantial copper residue was detected in the tissues of T. jarbua exposed to copper and the level of copper in tissues reduced when the fishes were treated with vitamins ensuring copper depuration and thereby protecting them against stress. We concluded that vitamin supplementation offered significant reduction of the oxidative stress mediated by copper and we discuss the possible application of vitamins in costal aquaculture process.     

Production of Candida utilis biomass as aquaculture feed

Fish offal-peat compost was hydrolysed and the resultant liquid extracts used as substrate in the cultivation of the yeast Candida utilis. The yeast was able to grow in this culture medium, attaining a growth yield of approximately 260 g biomass kg^?1 total carbohydrate consumed. The biomass produced had a good amino acid composition, with a protein content of 520 g kg^?1, and a relatively low lipid content. Dry yeast was used as a feed component in the diet of cultivated rainbow trout (Oncorhynchus mykiss) in which it substituted well for other, traditional sources of protein.     

Natural decoloration,composition and increase in dietary fibre content of an edible marine algae,Ulva rigida (Chlorophyta), grown under different nitrogen conditions

The colour, dietary fibre content and characteristics of the edible marine green algae, Ulva rigida, were investigated in relation with the nitrogen content of the algal culture medium. Colour brightness decreased and total nitrogen of the algae increased in nitrogen-enriched conditions. When nitrogen-enriched seaweeds were grown again in normal seawater for 10 days, colour brightness increased and total nitrogen concentration fell. Total dietary fibre content of the wild and nitrogen enriched algae were close (～38.0% DW) but increased markedly when the nitrogen-rich plants were cultured in normal sea-water (54.4% after 10 days). Soluble fibre were xylorhamnoglucuronan sulphate (ulvan) with close molar compositions for all the seaweed samples. Insoluble polysaccharides were composed of glucose, xylose, uronic acid, rhamnose and sulphate which molar proportions varied for the different algal samples. The soluble fibre intrinsic viscosity and the water holding capacity of insoluble fibre were not markedly affected by the growth conditions. This report demonstrates that edible seaweed aquaculture provides an alternative or a complement to post-harvest transformations of seaweeds to modify organoleptic and nutritional characteristics.     

Total mercury levels in commercial fish species from Italian fishery and aquaculture

ABSTRACT

Total mercury levels were measured in 42 commercial fish species caught off the Central Adriatic and Tyrrhenian coasts of Italy and in 6 aquaculture species. The study on wild fish covered species differing in living habitat and trophic level. The study on farmed fish covered marine and freshwater species from intensive and extensive aquaculture and their feed. Mercury levels were analysed by thermal decomposition–amalgamation–atomic absorption spectrophotometry. Total mercury concentrations in the muscle of wild fish showed a high variability among species (0.025–2.20 mg kg^?1 wet weight). The lowest levels were detected in low trophic-level demersal and pelagic–neritic fish and in young individuals of high trophic-level species. Levels exceeding the European Commission limits were found in large-size specimens of high trophic-level pelagic and demersal species. Fish from intensive farming showed low levels of total mercury (0.008–0.251 mg kg^?1). Fish from extensive rearing showed variable contamination levels, depending on the area of provenience. An estimation of the human intake of mercury associated to the consumption of the studied fish and its comparison with the tolerable weekly intake is provided.     

The effect of recirculating aquaculture systems on the concentrations of heavy metals in culture water and tissues of Nile tilapia Oreochromis niloticus

To date, farming fish in recirculating aquaculture systems (RAS) is one of the most environmentally friendly ways of producing fish. However, with the trend towards intensification, and consequently decrease in water exchange rates, these systems may accumulate substances, such as heavy metals, in the water and fish. Inductively-coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectroscope (ICP-MS) were used to determine Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn, in the water and fish (Nile tilapia Oreochromis niloticus). Three RAS were used, differing in daily water exchange rates (30, 70 and 1500 l/kg feed/d). The concentrations of As, Fe, Mn, Ni and Zn in the water increased with decreasing water exchange rates, suggesting an accumulation of heavy metals as more water was re-used. Such accumulation in the water was, however, not translated into accumulation in the liver and muscle. Accumulation of heavy metals was always higher in the liver than in the muscle; however, As reached 1.61 mg/kg wet weight in the muscle of fish farmed in RAS-70 l/kg feed/d. However, these levels are considerably lower than permissible safety levels for human consumption.