A comparison of techniques for studying oogenesis in the European eel Anguilla anguilla

[EN] A multi-technique approach was used to study the changes occurring in European eel Anguilla anguilla ovaries during hormonally-induced vitellogenesis. Aside from classic techniques used to monitor the vitellogenic process, such as ovary histology, fat content analysis, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and vitellogenin enzyme linked immunosorbent assay (ELISA), a new technique, Fourier-transform infrared (FT-IR) microspectroscopy, was used to analyse A. anguilla ovaries. The results from the different techniques provided different ways of approaching the same process. Although it is considered a time consuming approach, of all the employed techniques, histology provided the most direct evidences about vitellogenesis. SDS-PAGE and ELISA were also useful for studying vitellogenesis, whereas fat analysis cannot be used for this purpose. The FT-IR analysis provided a representative IR spectrum for each ovarian stage (previtellogenic stage, early vitellogenic stage, mid-vitellogenic stage and late vitellogenic stage), demonstrating that it is a valid method able to illustrate the distribution of the oocytes within the ovary slices. The chemical maps obtained confirmed changes in lipid concentrations and revealed their distribution within the oocytes at different maturational stages. When the results and the accuracy of the FT-IR analysis were compared with those of the traditional techniques commonly used to establish the vitellogenic stage, it became evident that FT-IR is a useful and reliable tool, with many advantages, including the fact that it requires little biological material, the costs involved are low, analysis times are short and last but not least, the fact that it offers the possibility of simultaneously analysing various biocomponents of the same oocyte. (C) 2016 The Fisheries Society of the British IslesThis study was funded by the European Community's 7th Framework Programme under the Theme 2, Food, Agriculture and Fisheries and Biotechnology, grant agreement number 245257 (PRO-EEL) and the COST Office (COST Action FA1205: AQUAGAMETE). I.M. had a pre-doctoral grant from Generalitat ValencianaMazzeo ., I.; Giorgini, E.; Gioacchini, G.; Maradonna, F.; Vilchez Olivencia, MC.; Baloche, S.; Dufour, S.... (2016). A comparison of techniques for studying oogenesis in the European eel Anguilla anguilla. Journal of Fish Biology. 89(4):2055-2069. doi:10.1111/jfb.13103S20552069894Asturiano, J. F., Perez, L., Garzon, D. L., Penaranda, D. S., Marco-Jimenez, F., Martinez-Llorens, S., … Jover, M. (2005). Effect of different methods for the induction of spermiation on semen quality in European eel. Aquaculture Research, 36(15), 1480-1487. doi:10.1111/j.1365-2109.2005.01366.xBradford, M. M. (1976). 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Feeding behaviour and digestion physiology in larval fish – current knowledge and gaps and bottlenecks in research

Food uptake follows rules defined by feeding behaviour that determines the kind and quantity of food ingested by fish larvae as well as how live prey and food particles are detected, captured and ingested. Feeding success depends on the progressive development of anatomical characteristics and physiological functions and on the availability of suitable food items throughout larval development. The fish larval stages present eco-morpho-physiological features very different from adults and differ from one species to another. The organoleptic properties, dimensions, detectability, movements characteristics and buoyancy of food items are all crucial features that should be considered, but is often ignored, in feeding regimes. Ontogenetic changes in digestive function lead to limitations in the ability to process certain feedstuffs. There is still a lack of knowledge about the digestion and absorption of various nutrients and about the ontogeny of basic physiological mechanisms in fish larvae, including how they are affected by genetic, dietary and environmental factors. The neural and hormonal regulation of the digestive process and of appetite is critical for optimizing digestion. These processes are still poorly described in fish larvae and attempts to develop optimal feeding regimes are often still on a ‘trial and error’ basis. A holistic understanding of feeding ecology and digestive functions is important for designing diets for fish larvae and the adaptation of rearing conditions to meet requirements for the best presentation of prey and microdiets, and their optimal ingestion, digestion and absorption. More research that targets gaps in our knowledge should advance larval rearing