Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Final Activity and Management Report Summary - RETDEV (Retinal development in flat fish larvae- the effect of dietary essential fatty acids)

The current proposal seeks to evaluate the effects of Highly unsaturated fatty acids (HUFA) in the development of the vision system in marine fish larvae under natural conditions. For over two centuries, researchers are investigating why fish populations fluctuate. Part of the answer is related with the survival of fish during their early life. Nowadays, scientists agree that quality of larval food is an important factor that benefits suitable larval development. Most marine fish larvae are visual feeders and also use vision to avoid predators, in consequence proper vision is fundamental for their survival.

The retina in vertebrates -including fish- is rich in HUFA, but fish larvae have low or no capacity to synthesise HUFA de novo, and therefore must incorporate them through the food. HUFA production in the marine ecosystem is mostly attributable to microalgae and they are ingested by fish larvae directly or mostly via zooplankton. Most of the attention about quality of food has been focused on aquaculture in order to design proper food to successfully rear different species in captivity, but how quality of food fluctuates in natural environments and in consequence how that affects natural fish population is not yet well understood. This information is relevant to determine natural causes of fish mortality and to predict how changes in the environment could affect fish recruitment.

This project was carried out at the Limnological Laboratory of the Faculty of Sciences, Universidad de la República (Uruguay). The study comprised different activities that included:
i) collection of microalgae, zooplankton and fish larvae from an Uruguayan estuary at different times of the year (spring, summer, early autumn);
ii) analysis of fatty acid profiles in algae and zooplankton as descriptors of the quality of food available for fish larvae;
iii) analysis of the structure and fatty acid composition of the retina from larvae capture at those periods.

In total, 48 samplings were performed along the study. Environmental conditions followed an expected seasonal pattern for most of the variables recorded. Levels of nutrients in the water were characteristic of natural environments with exception of high levels of phosphorous indicating that the studied system could be affected by anthropogenic activities. Microalgal composition varied between periods, spring was dominated by a cyptophyte Hyllea marina meanwhile a cyanophyte Synechocystis sp. dominated in summer and the diatom Melosyra sp. was the most abundant in early autumn.

A total of 12 fish taxa were recorded, which were mostly cited for the first time for the studied estuary. Larvae of Brevoortia aurea were abundant during spring meanwhile Prepilus parus dominated samples in summer and autumn. HUFA profiles in larvae and their food are under analysis but preliminary results on condition index of larvae estimated by an enzymatic approach showed that in spring the nutritional condition was lower than in the other periods.

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