Teleost fish larvae adapt to dietary arachidonic acid supply through modulation of the expression of lipid metabolism and stress response genes

Dietary fatty acid supply can affect stress response in fish during early development. Although knowledge on the mechanisms involved in fatty acid regulation of stress tolerance is scarce, it has often been hypothesised that eicosanoid profiles can influence cortisol production. Genomic cortisol actions are mediated by cytosolic receptors which may respond to cellular fatty acid signalling. An experiment was designed to test the effects of feeding gilthead sea-bream larvae with four microdiets, containing graded arachidonic acid (ARA) levels (0·4, 0·8, 1·5 and 3·0 %), on the expression of genes involved in stress response (steroidogenic acute regulatory protein, glucocorticoid receptor and phosphoenolpyruvate carboxykinase), lipid and, particularly, eicosanoid metabolism (hormone-sensitive lipase, PPARα, phospholipase A2, cyclo-oxygenase-2 and 5-lipoxygenase), as determined by real-time quantitative PCR. Fish fatty acid phenotypes reflected dietary fatty acid profiles. Growth performance, survival after acute stress and similar whole-body basal cortisol levels suggested that sea-bream larvae could tolerate a wide range of dietary ARA levels. Transcription of all genes analysed was significantly reduced at dietary ARA levels above 0·4 %. Nonetheless, despite practical suppression of phospholipase A2 transcription, higher leukotriene B4 levels were detected in larvae fed 3·0 % ARA, whereas a similar trend was observed regarding PGE2 production. The present study demonstrates that adaptation to a wide range of dietary ARA levels in gilthead sea-bream larvae involves the modulation of the expression of genes related to eicosanoid synthesis, lipid metabolism and stress response. The roles of ARA, other polyunsaturates and eicosanoids as signals in this process are discussed.

This study was supported by ‘Fundação para a Ciência e a Tecnologia’, (FCT, Portugal; EFARFish – ‘A new method for the study of essential fatty acid requirements in fish larvae’ PTDC/MAR/67017/2006); ‘Consolider – Ingenio 2010’ programme (Plan Nacional I+D+I+FEDER, Spain; ‘Aquagenomics – Improvement of aquaculture production by the use of biotechnological tools’ CSD2007-00002); MCYT+FEDER (Plan Nacional I+D+I, Spain; ‘Mejora del aprovechamiento del alimento en primeras edades de peces marinos: funcionalidad del tubo digestivo y valoración de la utilización de macronutrientes’ AGL2007-64450-C02-01); POCTEP Programme (0251-ECOAQUA-5-E). D. A. M. was supported by grant SFRH/BPD/32469/2006 (FCT, Portugal). The study also benefited from the LARVANET grants COST-STSM-FA0801-4496 and COST-STSM-FA0801-5429.

Peer Reviewed