Tissue effect on RNA:DNA ratios to the analysis of marine fish larvae condition.

OLIVAR, M. PILAR; DIAZ, MARINA VERA; CHÍCHARO, M. ALEXANDRA; MOROTE, ELVIRA

Kiel

Congreso; 32nd Annual larval fish coference; 2008

In some routine studies of larval condition based on RNA:DNA ratios, heads and/or guts are removed for further age and feeding analysis. Also, during capture larvae are often found missing eyes. In this work we analysed tissues effects (muscle tail, head, eye, gut and the whole larvae) on RNA:DNA ratios from different species (Sardina pilchardus, Engraulis encrasicolus, Atherina presbyter, Paralichthys orbignyanus) in different developmental stages (flexion and postflexion) from different locations (North-western Mediterranean, North-eastern Atlantic and South-eastern Atlantic) and water temperatures (14-25ºC). For all species and development phases, it was shown that the RNA:DNA ratios in head tissues were significantly lower than in muscle tail or gut. The comparison of RNA:DNA ratios of head with or without eyes did not show significant differences. When comparing two tail sections, RNA:DNA ratios where higher for the anterior body part in Sardina pilchardus and Engraulis encrasicolus larvae while no significant differences were found for Paralichthys orbignyanus larvae. As previous major starvation and growth experiments described in literature to determine critical ratios and calibration responses of fish larvae were done analysing the entire larvae, caution is needed when RNA:DNA ratios obtained not using the entire larvae are compared to these studies. We proposed, for the studied species, conversion factors to be applied to the RNA:DNA ratio data in order to classify starving larvae or to calculate growth rate, when only different body sections are analysed. As essential for interpretation of such data, it is discussed what tissues are the most appropriate to assess nutritional condition in fish larvae, based on trends in concentrations of nucleic acids and ratios during starvation experiments.