Carps, barbels and other cyprinids are the major contributors to freshwater aquaculture 41 at global scale. Nevertheless, freshwater fish aquaculture needs to diversify their 42 production in order to offer consumers new species. Tench (Tinca tinca) is a freshwater species with great interest for the diversification of continental aquaculture. However, 44 up to date, no commercial formulated diet exists for this species in order to optimize 45 their nutritional requirements and the quality of its final product. Using multiple 46 methodological approaches, the aim of this study was to evaluate the long chain 47 polyunsaturated fatty acid (LC-PUFA) metabolism of T. tinca. Firstly, the molecular 48 cloning and functional characterisation by heterologous expression in yeast of a 49 desaturase (Fads2) and two elongases (Elovl2 and Elovl5) involved in LC-PUFA 50 biosynthesis, and the analysis of gene expression among tissues were performed. 51 Secondly, in order to confirm the LC-PUFA biosynthesis capacity of isolated 52 hepatocytes and enterocytes, cells were incubated with [1-14 C] labelled linoleic acid 53 (18:2n-6, LA), linolenic acid (18:3n-3, ALA) and eicosapentaenoic acid (20:5n-3, 54 EPA). In yeast, Fads2 showed a Δ6/Δ5 bifunctional activity. Elovl2 was more active 55 over C 20 and C 22 substrates, whereas Elovl5 was over C 18 and C 20 . Liver displayed the 56 highest expression for the three target genes (fads2, elovl2 and elovl5). Incubated cells 57 also showed Fads2 bifunctional activity as well as elongation products in concordance 58 with yeast heterologous expression results. Importantly, our results demonstrated that 59 tench is able to biosynthesise docosahexaenoic acid (DHA) from 18:3n-3 in both 60 hepatocytes and enterocytes, a capacity that seems to explain in part the surprisingly 61 high levels of DHA found in the fish flesh compared to its dietary supply. Tench is a 62 promising freshwater species with a potential capacity to endogenously increase its 4 63 flesh DHA contents, reducing the impact that the usage of fish oils from forage fisheries 64 may have on the aquaculture industry.

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A study of oxygen injection was performed in a completely filled gravity pipe, which is part of the South Tenerife reclaimed wastewater reuse scheme (Spain), in order to inhibit the appearance of anaerobic conditions by a nitrification-denitrification process. The pipe was 0.6 m in diameter and 62 km long and made of cast iron with a concrete inner coating, A high-pressure oxygen injection system was installed at 16 km from the pipe inlet, where severe anaerobic conditions appear. Experiments on oxygen injection were carried out with three different concentrations (7, 15 and 30 mg l(-1) O2). In all experiments, oxygen dissolved properly after injection, and no gas escapes were detected during water transportation. Most oxygen was consumed in the nitrification process, due to the low COD/NH4-N ratio, leading to a maximum production of oxidized nitrogen compounds of 7.5 mg l(-1) NO(x)-N with the 30 mg l(-1) O2 dose. Nitrification occured with nitrite accumulation, attributed to the presence of free ammonia within the range 1.2-1.4 mg l(-). Once the oxygen had been consumed, an apparent half-order denitrification took place, with limitation of biodegradable organic matter. The anoxic conditions led to a complete inhibition of sulphide generation.

Fish vary in their ability to biosynthesise long-chain polyunsaturated fatty acids (LC-PUFA) depending upon the complement and function of key enzymes commonly known as fatty acyl desaturases and elongases. It has been reported in Solea senegalensis the existence of a Δ4 desaturase, enabling the biosynthesis of docosahexaenoic acid (DHA) from eicosapentaenoic acid (EPA), which can be modulated by the diet. The present study aims to evaluate the combined effects of the partial replacement of fish oil (FO) with vegetable oils and reduced environmental salinity in the fatty acid composition of relevant body compartments (muscle, hepatocytes and enterocytes), the enzymatic activity over α-linolenic acid (ALA) to form n-3 LC-PUFA through the incubation of isolated hepatocytes and enterocytes with [1-14C] 18:3 n-3, and the regulation of the S. senegalensis fads2 and elovl5 in the liver and intestine. The presence of radiolabelled products, including 18:4n-3, 20:4n-3 and EPA, provided compelling evidence that a complete pathway enabling the biosynthesis of EPA from ALA, establishing S. senegalensis, has at least one Fads2 with ∆6 activity. Dietary composition prevailed over salinity in regulating the expression of fads2, while salinity did so over dietary composition for elovl5. FO replacement enhanced the proportion of DHA in S. senegalensis muscle and the combination with 20 ppt salinity increased the amount of n-3 LC-PUFA in hepatocytes.